Tuesday, October 26, 2010

New Periodic Table with up to Z=172 Element

An extended periodic table with 54 predicted elements has been mapped out by a chemist in Finland.
The periodic table of the elements was proposed in 1869 by Dimitri Mendeleev. The value of his scheme for organising the elements was proven by the prediction of the existence and properties of then unknown elements including gallium (first isolated in 1875).

Now Pekka Pyykkö at the University of Helsinki has used a highly accurate computational model to predict electronic structures and therefore the periodic table positions of elements up to proton number 172 - far beyond the limit of elements that scientists can currently synthesise.

New Periodic Table-2010
The extra 54 super heavy elements predicted by Pyykkö may exist under extreme conditions with very short lifetimes owing to radioactive decay, but have not yet been synthesised.

Read the Original Article:

A suggested periodic table up to Z 172, based on Dirac–Fock calculations on atoms and ions
Pekka Pyykkö, Phys. Chem. Chem. Phys., 2010
DOI: 10.1039/c0cp01575j

Sunday, October 24, 2010

Cooling Baths

Any temprature you want, using about 50 combinations os Salt/ice, Solvent/dry ice, and Solvent/liquid N2 - Very handy.

Cooling Baths*
Temperature
Composition
13
p-Xylene/CO2(s)
12
Dioxane/CO2(s)
6
Cyclohexane/CO2(s)
5
Benzene/CO2(s)
2
Formamide/CO2(s)
0
Crushed Ice
-5 -> -20
Ice/Salt
-10.5
Ethylene Glycol/CO2(s)
-12
Cycloheptane/CO2(s)
-15
Benzyl alcohol/CO2(s)
-22
Tetrachloroethylene/CO2(s)
-22.8
Carbon Tetrachloride/CO2(s)
-25
1,3-Dichlorobenezene/CO2(s)
-29
o-Xylene/CO2(s)
-32
m-Toluidine/CO2(s)
-41
Acetonitrile/CO2(s)
-42
Pyridine/CO2(s)
-47
m-Xylene/CO2(s)
-56
n-Octane/CO2(s)
-60
Isopropyl Ether/CO2(s)
-77
Acetone/CO2(s)
-77
Butyl Acetate/CO2(s)
-83
Propyl Amine/CO2(s)
-83.6
Ethyl Acetate/Liq N2
-89
n-Butanol/Liq N2
-94
Hexane/Liq N2
-94.6
Acetone/Liq N2
-95.1
Toluene/Liq N2
-98
Methanol/Liq N2
-100
Ehtyl Ether/CO2(s)
-104
Cyclohexane/Liq N2
-116
Ethanol/Liq N2
-116
Ethyl Ether/Liq N2
-131
n-Pentane/LiqN2
-160
Isopentane/Liq N2
-196
Liq N2

Carboxylic acid Acidity : Inductive Effect vs Resonance Effect

Organic Chemistry Reasoning Questions - 4

CSIR, GATE, JAM, IISc, and all other Chemistry Higher studies Exams has been changed their syllabus. If we analyze them quite precisely and it’s seems that many advanced are of research has been included. The previous year’s questions from those type exams are clearly indicated that, students must understand the fundamentals, and they must have reasoning ability to answer the question. In this view we wish to collect most important exam based reasoning questions and we discussed answer for them. It’s not only useful for competitive exams also for your interviews.


Arrange the following carboxylic acid according to their acid strength.
Answer:
Dear readers, This type questions often appeared in all chemistry competitive exams. In order to answer this question, we need to know, which are the factors affecting the acidity of the carboxylic acid.
1.      Equilibrium Acidity
2.      Solvent Effects
3.      Hybridization
4.      Stereoelectronic Control of Enolization
5.      Kinetic Acidity
6.      Substituent Effects on the Acidity
7.      Conjugation and Hybridization
8.      Ortho effect
9.      Hydrogen bonding
In the case of carboxylic acids, if the electrophilic character of the carbonyl carbon is decreased the acidity of the carboxylic acid will also decrease. Similarly, an increase in its electrophilicity will increase the acidity of the acid.

Electron donating substituent decreases the acidity. Electronegative substituents increase acidity by inductive electron withdrawal. Higher the electronegativity of the substituent the greater the increase in acidity (F > Cl > Br > I), and the closer the substituent is to the carboxyl group the greater is its effect.
Oxygen has a much larger electronegativity than carbon, but it is an excellent p-π electron donor to sp2 carbon functions. For the meta isomer, the inductive effect is somewhat stronger than the resonance donation, but the para-isomer is able to donate an oxygen electron pair directly into the electrophilic carboxyl function. Both the meta and para-nitro substituent withdraw electrons from the benzene ring by a combination of inductive and resonance action, and the corresponding acids are greatly strengthened.
Inductive Effect vs Resonance Effect
Substituents have both an inductive effect and a resonance effect. This creates a number of different behaviours when it comes to such things as the reactivity of substituted benzenes towards electrophilic substitution. For example:

Inductive = electron donating ; Resonance = electron donating:
Ortho/para directing. Meta positions have increased reactivity relative to benzene.
Examples of substituent: alkyl

Inductive = electron withdrawing ; Resonance = electron withdrawing:
Meta directing. Meta positions have decreased reactivity relative to benzene.
Examples of substituent: nitro, carboxyl, sulfonyl, quaternary ammonium.

Inductive = electron withdrawing ; Resonance = electron donating ; Resonance > Inductive:Ortho/para directing. Ortho/para positions have increased reactivity relative to benzene. Meta positions have decreased reactivity relative to benzene.
Examples of substituent: hydroxy, alkoxy, amino, acylamido.

Inductive = electron withdrawing ; Resonance = electron donating ; Resonance < Inductive:Ortho/para directing. Ortho/para positions have decreased reactivity relative to benzene. Meta positions have decreased reactivity relative to benzene.
Examples of substituent: fluoro, chloro.

Saturday, October 23, 2010

Organic Chemistry Reasoning Questions - 3

CSIR, GATE, JAM, IISc, and all other Chemistry Higher studies Exams has been changed their syllabus. If we analyze them quite precisely and it’s seems that many advanced are of research has been included. The previous year’s questions from those type exams are clearly indicated that, students must understand the fundamentals, and they must have reasoning ability to answer the question. In this view we wish to collect most important exam based reasoning questions and we discussed answer for them. It’s not only useful for competitive exams also for your interviews.

Today's Question is related to Organic Chemistry Reasoning Questions-1

  Why o-nitrophenol is much more volitile than p-nitrophenol?
Answer:
Dear readers, we have seen before, Hydrogen-bonding leads to an increase in intermolecular ‘aggregation’ forces and is manifested particularly in the boiling point and solubility of the organic compound.
But, Intramolecular hydrogen-bonds can also be formed, and and are of particular significance when the resulting ring is five- or six- membered. This is called chelation.
Since chelation does not rise to intermolecular aggregation forces, chelated compounds have normal boiling point. para-nitrophenol forms intermolecular hydrogen-bonds.

Bio LED

Can street lights be replaced by trees? Taiwanese scientists believe that they can using gold nanoparticles to induce luminescence in leaves.

Bio LED

Light emitting diodes (LEDs) are used in street and bicycle lights as they have a higher efficiency than traditional light bulbs but even more environmentally-friendly LED's are desirable. Now Yen Hsun Su and coworkers at Academia Sinica and the National Cheng Kung University in Taipei and Tainan have tackled this problem by synthesising gold nanoparticles shaped like sea urchins and diffusing them into plant leaves to create bio-LEDs.

Chlorophyll shows bioluminescence upon high wavelength (400 nm) ultra violet excitation. In contrast, the gold nanoparticles are excited at shorter wavelengths and emit at 400 nm. By implanting the nanoparticles into Bacopa caroliniana plants, Su was able to induce the chlorophyll in the leaves to produce a red emission. In addition, the nanoparticles are able to suppress emission blinking - a known problem for gold nanoparticles -as they have a strong surface plasmon resonance which localises light on the nanoscale.

Gold nanoparticles in the leaves induce bioluminescence

The bio-LED could be used to make roadside trees luminescent at night. This will save energy and absorb CO2 as the bio-LED luminescence will cause the chloroplast to conduct photosynthesis,' says Su.

The way the researchers introduce these gold nano-sea urchins in live plants utilising the 400 nm photoluminescence of gold to obtain the bioluminescence of chlorophyll is impressive,' comments Krishanu Ray, an expert in nanotechnology and fluorescence at the University of Maryland in the US. 'Proper optimisation and tuning could potentially result in stronger bioluminescence,' he adds.

The researchers agree that bioluminescence efficiency needs to be improved and are also looking to apply the same strategy to other plant biomolecules.

Link to Full Article:
Influence of surface plasmon resonance on the emission intermittency of photoluminescence from gold nano-sea-urchins

Yen Hsun Su, Sheng-Lung Tu, Shih-Wen Tseng, Yun-Chorng Chang, Shih-Hui Chang and Wei-Min Zhang, Nanoscale, 2010
DOI: 10.1039/c0nr00330a
For the original storie:
http://www.rsc.org/Publishing/ChemTech/Volume/2010/11/leaves_glow.asp

Friday, October 22, 2010

Organic Chemistry Reasoning Questions - 2

CSIR, GATE, JAM, IISc, and all other Chemistry Higher studies Exams has been changed their syllabus. If we analyze them quite precisely and it’s seems that many advanced are of research has been included. The previous year’s questions from those type exams are clearly indicated that, students must understand the fundamentals, and they must have reasoning ability to answer the question. In this view we wish to collect most important exam based reasoning questions and we discussed answer for them. It’s not only useful for competitive exams also for your interviews.

 
Often resonance effect based questions are raised in all chemistry compettive exams.
For example:
Give reason: phenanthrene have more stabilization energy than anthracene?
Answer:

In general, for compounds containing equal numbers of benzene rings, that for which the greatest number of Kekule structure can be drawn has the largest stabilization energy.


Anthracene Resonance Strectures


Phenanthrene Resonance Strectures
Due to higher number of phenanthren resonance forms, it has more stabilization energy.

 Tomorrow we will see some other reasoning questions.

Emerging Technologies on Biofuels Generations

Biofuel

Review by Stanislav Miertus et al., describes, how next-generation biofuels, such as cellulosic bioethanol, biomethane from waste, synthetic biofuels obtained via gasification of biomass, biohydrogen, and others are currently in the centre of attention of technologists and policy makers in search of a more sustainable biofuel of tomorrow. In order to set realistic targets for the future biofuel options, it is important to assess their sustainability according to technical, economic, and environmental points of view. Opportunities and limits are discussed in terms of technical applicability of existing and emerging technology options to bio-waste feedstock, and further development forecasts are made based on the existing social-economic and market situation, feedstock potentials, and other global aspects.


Full article:
Next-Generation Biofuels: Survey of Emerging Technologies and Sustainability Issues.
Sergey Zinoviev, Franziska Müller-Langer, Piyali Das, Nicolás Bertero, Paolo Fornasiero, Martin Kaltschmitt, Gabriele Centi and Stanislav Miertus


Thursday, October 21, 2010

Organic Chemistry Reasoning Questions - 1

CSIR, GATE, JAM, IISc, and all other Chemistry Higher studies Exams has been changed their syllabus. If we analyze them quite precisely and it’s seems that many advanced are of research has been included. The previous year’s questions from those type exams are clearly indicated that, students must understand the fundamentals, and they must have reasoning ability to answer the question. In this view we wish to collect most important exam based reasoning questions and we discussed answer for them. It’s not only useful for competitive exams also for your interviews.
Today's Question:

2,4-pentanedione(A) in hexane exit 8% of keto tautomer and 92% of the enol tautomer.

Q1. Why (A) prefer to form B??
Q2. Give Reason: In water 2,4-penatanedione consist of 84% of keto  and 16% enol tautomer.
Answer:
A1. Hydrogen Bonding.

A2. In water, The Keto tautomer is stabilized by hydrogen-bonding of its two carbonyl-oxygen atoms with the solvent, effectively nullifying one of the stabilizing influence in the enol tautomer.
The boiling point of ethanol is very much higher than that of its isomer, dimethyl ether. Why?
Answer:
Hydrogen Bonding. Hydrogen-bonding leads to an increase in intermolecular ‘aggregation’ forcesand is manifested particularly in the boiling point and solubility of organic compound. The boiling point is raised because energy is required to separate H –bonded molecules. That’s why ethanol boiling point is higher than that of dimethyl ether.

We can see other questions tomorrow.

Wednesday, October 20, 2010

GATE- CHEMISTRY(CY) PREVIOUS YEAR QUESTION PAPERS (Downlode)


GATE is the gate for entering Masters and Doctoral programmers.

The Indian Institute of Science and seven Indian Institutes of Technology jointly conduct Graduate Aptitude Test (GATE) for Engineering students. On behalf of National Coordination Board – GATE, the Department of Higher Education, Ministry of Human Resource Development (MHRD), Government of India, the test is organised at national level. For regulating the examination and declaring the results, GATE committee is the only responsible authority, which involves representatives from administering institutes.

Admission into postgraduate programmes with MHRD and some other government assistantships/ scholarships in engineering institutes/ colleges can be acquired by GATE qualifying candidates. Eligibility for admission into Doctoral/ Master programmes in Architecture/ Technology/ Engineering as well as Doctoral programmes in other related Science branches with MHRD or other government assistantships / scholarships is Bachelor’s degree in Technology/ Engineering/ Architecture or Master’s degree in any area of Mathematics/ Science/ Computer Applications/ Statistics. The students, who secure a place into a postgraduate programme, according to the existing procedure of the relevant institution, are eligible for scholarship as well. However, Candidates with Masters in Technology/ Engineering/ Architecture may get admission into PhD programmes with assistantship/ scholarship without going through GATE exams.

GATE qualification is compulsory in few of the institutions, and it's equally applicable on self-financing students to postgraduate programmes. GATE Qualifying candidates are eligible for Junior Research Fellowship award in CSIR Laboratories or sponsored projects by CSIR. Students coming to the top in some of the GATE papers can apply for “Shyama Prasad Mukherjee Fellowship”, which is given by CSIR. Prerequisite for an Engineer or Scientist at government organisation is sometimes GATE.
A huge number of aspirants go for the test, but for sure the qualifying number is very less in comparison. Hence, GATE papers of previous years can save you from failing the test. You need to work hard on the papers of back years. Generally, they are objective type multiple choice questions. The paper structure is given below for your reference-

Multiple choice questions in all papers and sections will contain four answers, of which only one is correct. The types of questions in a paper may be based on following logic:

(i) Recall:

These are based on facts, principles, formulae or laws of the discipline. The candidate is expected to be able to obtain the answer either from his/her memory of the subject or at most from a one-line computation.

Example

Q. During machining maximum heat is produced

(A) in flank face  (B) in rake face  (C) in shear zone  (D) due to friction between chip and tool

(ii) Comprehension:

These questions will test the candidate's understanding of the basics of his/her field, by requiring him/her to draw simple conclusions from fundamental ideas.

Example

Q. A DC motor requires a starter in order

(A) to develop a starting torque

(B) to compensate for auxiliary field ampere turns

(C) to limit armature current at starting

(D) to provide regenerative braking

(iii) Application:

In these questions, the candidate is expected to apply his/her knowledge either through computation or by logical reasoning.

Example:

Q. The sequent depth ratio of a hydraulic jump in a rectangular channel is 16.48. The Froude number at the beginning of the jump is:

(A) 10.0  (B) 5.0  (C) 12.0  (D) 8.0

(iv) Analysis and Synthesis:

These can be linked questions, where the answer to the first question of the pair is required in order to answer its successor. Or these can be common data questions, in which two questions share the same data but can be solved independently of one another.

Common data questions

Multiple questions may be linked to a common data problem, passage and the like. Two or three questions can be formed from the given common data problem. Each question is independent and its solution obtainable from the above problem data/passage directly. (Answer of the previous question is not required to solve the next question). Each question under this group will carry two marks.

Example

Common Data, for instance, Questions 48 and 49 in main paper:

Let X and Y be jointly distributed random variables such that the conditional distribution of Y, given X=x, is uniform on the interval (x-1,x+1). Suppose E(X)=1 and Var(X)= 5/3

First question using common data:

Q.48 The mean of the random variable Y is

(A) 1/2 (B) 1 (C) 3/2 (D) 2

Second question using common data:

Q.49 The variance of the random variable Y is

(A) 1/2 (B) 2/3 (C) 1 (D) 2

Linked answer questions:

These questions are of problem solving type. A problem statement is followed by two questions based on the problem statement. The two questions are designed such that the solution to the second question depends upon the answer to the first one. In other words, the first answer is an intermediate step in working out the second answer. Each question in such linked answer questions will carry two marks.

Example:

Statement for Linked Answer Questions, for instance, for Questions 52 and 53 in Main Paper:

The open loop transfer function of a unity feedback control system is given by
First question of the pair:

Q.52 The value of K which will cause sustained oscillations in the closed loop system is
Second question of the pair:

Q.53 The frequency of sustained oscillations is
The questions based on the above four logics may be a mix of single stand alone statement / phrase / data type questions, combination of option codes type questions or match items types questions.

What is New in GATE 2011?

ONLINE examination in two additional papers:

In GATE 2010, the papers with codes MN and TF had ONLINE examination. In GATE 2011, two additional papers AE and GG will also have ONLINE examination. The ONLINE examination will be conducted in two sessions on Sunday, January 30, 2011. The ONLINE examination in GG and TF will be held in the forenoon session from 09.00 hrs to 12.00 hrs. The ONLINE examination in AE and MN will be held in the afternoon session from 14.00 hrs to 17.00 hrs.

Numerical answer type questions in AE and TF papers:

In AE and TF papers, the question paper will consist of 60 questions of multiple choice type and 5 questions of numerical answer type. For multiple choice type questions, each question will have four choices for the answer. For numerical answer type questions, each question will have a number as the answer.

OFFLINE examination in two sessions:

In GATE 2011, the OFFLINE examination will be conducted in two sessions on Sunday, February 13, 2011. The OFFLINE examination in AR, BT, CE, CH, CS, ME, PH and PI papers will be held in the forenoon session from 09.00 hrs to 12.00 hrs. The OFFLINE examination in AG, CY, EC, EE, IN, MA, MT, XE and XL will be held in the afternoon session from 14.00 hrs to 17.00 hrs.

Food Technology section in both XE and XL papers:

In GATE 2011, Food Technology will be introduced as an optional section in XL paper also. The structure for Food Technology section in XL paper will be the same as the structure of the other optional sections in XL paper. The structure for Food Technology section in XE paper will the same as the structure of the other optional sections in XE paper. The syllabus for the Food Technology section in XE and XL papers is the same.

Hence, let's prepare in advance for the exams and try to solve more and more GATE Sample papers from various websites, such as latestt.com. This site, not only gives you maximum of everything at one place, but also saves your valuable time on searching or browsing things, here and there online. Forums, free file Sharing and message boards are the biggest facilities available to all the students. Best of luck for future and hope that you rock in the test after all the odds!

GATE - Chemistry(CY) Previous Year Question papers Downlode:

2010 GATE Chemistry Question Paper


2010 GATE Chemistry Answers

2009 GATE Chemistry Question Paper

2008 GATE Chemistry Question Paper


2007 GATE Chemistry Question Paper


2011 GATE Syllabous for Chemistry (CY)

2011 GATE - General Aptitude (GA) Model Paper

Important Dates

Commencement of sale of Application Form and Information Brochure - Tuesday September 21, 2010

Commencement of Online Application Form submission -Tuesday September 21, 2010 (09:00 Hrs onwards)

Last date for issue of Information Brochure and Application Form at Bank Counters - Wednesday October 27, 2010

Last date for issue of Information Brochure and Application Form at zonal GATE office counters - Friday October 29, 2010

Last date for Submission of Online Application Form (website closure) - Wednesday October 27, 2010 (18:00 Hrs)

Last date for the Receipt of completed Offline/Online Application Form at the respective zonal GATE Office - Tuesday November 02, 2010

Website display of final list of registered candidates, choices of test paper and examination city - Friday December 10, 2010

Date for reporting any discrepancy in the choice of examination cities or in the choice of GATE paper - Friday December 31, 2010

Date for reporting the non-receipt of admit cards for ONLINE examination papers - Thursday January 20, 2011

Last date for reporting the non-receipt of admit cards for OFFLINE examination papers - Monday January 31, 2011

GATE 2011 Online Examination Papers: GG and TF Sunday January 30, 2011 (09:00 Hrs to 12:00 Hrs)

GATE 2011 Online Examination Papers: AE and MN Sunday January 30, 2011 (14:00 Hrs to 17:00 Hrs)

GATE 2011 Offline Examination Papers: AR, BT, CE, CH, CS, ME, PH and PI Sunday February 13, 2011 (09:00 Hrs to 12:00 Hrs)

GATE 2011 Offline Examination Papers: AG, CY, EC, EE, IN, MA, MT, XE and XL Sunday February 13, 2011 (14:00 Hrs to 17:00 Hrs)

Announcement of results - Tuesday March 15, 2011 (10:00 Hrs)

Sunday, October 17, 2010

JOINT ADMISSION TEST (JAM) - Chemistry Question papers downlodes


JOINT ADMISSION TEST (JAM)

The Indian Institutes of Technology (IITs) are institutions of national importance established through an Act of Parliament. The IITs are well known, the world over, for quality education in engineering and science, and research in frontier areas. The aim of IITs is to build sound foundation of knowledge, pursue excellence and enhance creativity in intellectually stimulating environment. The current pace of advancement of technology needs a coherent back up of ba sic science education and research. The vibrant academic ambience and research infrastructure of the IITs motivate the students to pursue Research and Development careers in frontier areas of basic sciences as well as interdiscipli nary areas of science and technology. IITs have well equipped modern laboratories, efficient computer networks and state of the art libraries. The teaching process is structured to promote close and continuous contact between the faculty and the students. A number of financial assistantships and freeships are available to SC/ST and other deserving and meritorious students at individual institutes.

From the Academic Session 2004 - 2005, Indian Institutes of Technology have started conducting a Joint Admission test for M.Sc. (JAM) for admission to M.Sc. and other post-B.Sc. programs at the IITs. The main objective of JAM is to provide admissions to various M.Sc., Joint M.Sc.-Ph.D., M.Sc.-Ph.D. Dual degree and other post-B.Sc. programs based on the performance in a single test and consolidate 'Science' as a career option for bright students from across the country. In due course, JAM is also expected to become a benchmark for normalising undergraduate level science education in the country.

The M.Sc., Joint M.Sc.-Ph.D., M.Sc.-Ph.D. Dual degree and other post-B.Sc. programs at the IITs offer high quality post-B.Sc. education in respective disciplines, comparable to the best in the world. The curricula for these programs are designed to provide the students opportunities to develop academic talent leading to challenging and rewarding professional life. The curricula are regularly updated at each IIT. Interdisciplinary content of the curricula equips the students to utilize scientific knowledge for practical applications. The medium of instruction in all the programs is English.

Syllabus:

CHEMISTRY (CY)

PHYSICAL CHEMISTRY 
Basic Mathematical Concepts: Differential equations, vectors and matrices.
Atomic Structure: Fundamental particles. Bohr's theory of hydrogen atom; Wave-particle duality; Uncertainty principles; Schrdinger's wave equation; Quantum numbers, shapes of orbitals; Hund's rule and Pauli's exclusion principle.

Theory of Gases: Kinetic theory of gases. Maxwell-Boltzmann distribution law; Equipartition of energy. Chemical Thermodynamics: Reversible and irreversible processes; First law and its application to ideal and nonideal gases; Thermochemistry; Second law; Entropy and free energy, Criteria for spontaneity.

Chemical and Phase Equilibria: Law of mass action; Kp , Kc, Kx and Kn ; Effect of temperature on K; Ionic equilibria in solutions; pH and buffer solutions; Hydrolysis; Solubility product; Phase equilibria-Phase rule and its application to one-component and two-component systems; Colligative properties.

Electrochemistry: Conductance and its applications; Transport number; Galvanic cells; EMF and Free energy; Concentration cells with and without transport; Polarography.

Chemical Kinetics: Reactions of various order, Arrhenius equation, Collision theory; Theory of absolute reaction rate; Chain reactions - Normal and branched chain reactions; Enzyme kinetics; Photophysical and photochemical processes; Catalysis.

ORGANIC CHEMISTRY 

Basic Concepts in Organic Chemistry and Stereochemistry: Isomerism and nomenclature, electronic (resonance and inductive) effects. Optical isomerism in compounds containing one and two asymmetric centers, designation of absolute configuration, conformations of cyclohexanes.

Aromaticity and Huckel's rule: Mono and bicyclic aromatic hydrocarbons.

Organic Reaction Mechanism and Synthetic Applications: Methods of preparation and reactions of alkanes, alkenes, alkynes, arenes and their simple functional derivatives. Mechanism and synthetic applications of electrophilic aromatic substitution. Stereochemistry and mechanism of aliphatic nucleophilic substitution and elimination reactions. Mechanism of aldol condensation, Claisen condensation, esterification and ester hydrolysis, Cannizzaro reaction, benzoin condensation. Perkin reaction, Claisen rearrangement, Beckmann rearrangement and Wagner-Meerwein rearrangement. Synthesis of simple molecules using standard reactions of organic chemistry. Grignard reagents, acetoacetic and malonic ester chemistry.

Natural Products Chemistry: Introduction to the following classes of compounds-alkaloids, terpenes, carbohydrates, amino acids, peptides and nucleic acids.

Heterocyclic Chemistry: Monocyclic compounds with one hetero atom.

Qualitative Organic Analysis: Functional group interconversions, structural problems using chemical reactions, identification of functional groups by chemical tests.

INORGANIC CHEMISTRY 

Periodic Table: Periodic classification of elements and periodicity in properties; general methods of isolation and purification of elements.

Chemical Bonding and Shapes of Compounds: Types of bonding; VSEPR theory and shapes of molecules; hybridization; dipole moment; ionic solids; structure of NaCl, CsCl, diamond and graphite; lattice energy.
Main Group Elements (s and p blocks): Chemistry with emphasis on group relationship and gradation in properties; structure of electron deficient compounds of main group elements and application of main group elements.

Transition Metals (d block): Characteristics of 3d elements; oxide, hydroxide and salts of first row metals; coordination complexes; VB and Crystal Field theoretical approaches for structure, colour and magnetic properties of metal complexes.

Analytical Chemistry: Principles of qualitative and quantitative analysis; acid-base, oxidation-reduction and precipitation reactions; use of indicators; use of organic reagents in inorganic analysis; radioactivity; nuclear reactions; applications of isotopes.

Chemistry Question papers




The Periodic Table – History of Its Arrangement

The Periodic Table – History of Its Arrangement

Elements in Disorder
There is a curious parallel in the histories of the organic chemistry and inorganic chemistry of the nineteenth century. The opening decades of the century saw a puzzling proliferation in the number of organic compounds, and also in the number of elements. The third quarter of the century saw the realm of organic compounds reduced to order, thanks to Kekule's structural formula. It saw the realm of elements reduced to order also, and at least part of the credit for both changes goes to events at a particular international meeting of chemists.

But let's begin with the disorder at the beginning of the century.

The discovery of elements over and above the nine known to the ancients and the four studied by medieval alchemists has been previously discussed. The gaseous elements, nitrogen, hydrogen, oxygen, and chlorine, had all been discovered in the eighteenth century. So had the metals, cobalt, platinum, nickel, manganese, tungsten, molybdenum, uranium, titanium, and chromium.

In the first decade of the nineteenth century, no less than fourteen new elements were added to the list. Among the chemists already mentioned in this work, Davy had isolated no fewer than six by means of electrolysis. Gay-Lussac and Thenard had isolated boron; Wollaston had isolated palladium and rhodium, while Berzelius had discovered cerium.

Then, too, the English chemist Smithson Tennant (1761-1815), for whom Wollaston had worked as an assistant, discovered osmium and iridium. Another English chemist, Charles Hatchett (c.1765-1847), isolated columbium (now officially called niobium), while a Swedish chemist, Anders Gustaf Ekebert (1767-1813), discovered tantalum.

The haul in succeeding decades was not quite as rich, but the number of elements continued to mount. Berzelius discovered four more elements: selenium, silicon, zirconium, and thorium. Louis Nicolas Vauquelin in 1797 discovered beryllium.

By 1830, fifty-five different elements were recognized, a long step from the four elements of ancient theory. In fact, the number was too great for the comfort of chemists. The elements varied widely in properties and there seemed little order about them. Why were there so many? And how many more yet remained to be found? Ten? Fifty? A hundred? A thousand? An infinite number?

It was tempting to search for order in the list of elements already known. Perhaps in this manner some reason for the number of elements might be found and some way of accounting for the variation of properties that existed.

The first to catch a glimmering of order was the German chemist Johann Wolfgang Dobereiner (1780-1849). In 1829, he noted that the element bromine, discovered three years earlier by the French chemist Antoine Jerome Balard (1802-1876), seemed just halfway in its properties between chlorine and iodine. (Iodine had been discovered by another French chemist, Bernard Courtois (1777-1838), in 1811.) Not only did chlorine, bromine, and iodine show a smooth gradation in such properties as color and reactivity, but the atomic weight of bromine seemed to lie just midway between those of chlorine and iodine. Coincidence?

Dobereiner went on to find two other groups of three elements exhibiting neat gradations of properties: calcium, strontium, and barium; and sulfur, selenium, and tellurium. In both groups the atomic weight of the element in the middle was about midway between those of the other two. Coincidence again?

Dobereiner called these groups "triads", and searched unsuccessfully for others. The fact that five-sixths of the known elements could not be fitted into any triad arrangement made chemists decide that Dobereiner's findings were merely coincidence. Furthermore, the manner in which atomic weights fit along with the chemical properties among the elements of Dobereiner's triads did not impress chemists generally. In the first half of the nineteenth century, atomic weights tended to be underestimated. They were convenient in making chemical calculations, but there seemed no reason to use them in making lists of the elements.

In was even doubtful that atomic weights were useful in making chemical calculations. Some chemists did not distinguish carefully between atomic weight and molecular weight; some did not distinguish between atomic weight and equivalent weight. Thus, the equivalent weight of oxygen is 8, the atomic weight is 16, and the molecular weight is 32. In chemical calculations the equivalent weight, 8, is handiest; why then should the number 16 by used to determine the place of oxygen in the list of elements?

This confusion among equivalent weight, atomic weight, and molecular weight spread its disorganizing influence not merely over the question of the list of elements but into the study of chemistry generally. Disagreements over the relative weights to assign to different atoms led to disagreements over the number of atoms of particular elements within a given molecule.

Kekule, shortly after he had published his suggestions leading to structural formulas, realized this concept would come to nothing if chemists could not agree, first of all, on empirical formulas. He therefore suggested a conference of important chemists from all over Europe to discuss the matter. As a result, an international scientific meeting was held for the first time in history. It was called the First International Chemical Congress, and it met in 1860 in the town of Karlsruhe, in Germany.

One hundred forty delegates attended, among them the Italian chemist Stanislao Cannizzaro (1826-1910). Two years earlier, Cannizzaro had come across the work of his countryman Avogadro. He saw how Avogadro's hypothesis could be used to distinguish between the atomic weight and molecular weight of the important gaseous elements and how this distinction would serve to clarify the matter of atomic weights for the elements generally. Furthermore, he saw the importance of distinguishing carefully between atomic weight and equivalent weight.

At the Congress he made a strong speech on the subject and then distributed copies of a pamphlet in which he explained his points of view. Slowly and laboriously, he won over the chemical world to his views. From that time forward, the matter of atomic weight was clarified and the importance of berzelius's table of atomic weights was appreciated.

In organic chemistry this development meant that mean could now agree on empirical formulas and proceed onward to add detail in structural form, first in two dimensions, then in three.
In inorganic chemistry, the results were just as fruitful, for there was now at least one rational order in which to arrange the elements - in order of increasing atomic weight. Once that was done, chemists could look at the list with fresh eyes.

Organizing the Elements

In 1864, the English chemist John Alexander Reina Newlands (1837-1898) arranged the known elements in order of increasing atomic weights, and noted that this arrangement also placed the properties of the elements into at least a partial order. When he arranged his elements into vertical columns of seven, similar elements tended to fall into the same horizontal rows. Thus, potassium fell next to the very similar sodium; selenium fell in the same row as the similar sulfur; calcium next to the similar magnesium, and so on. Indeed, each of Dobereiner's three triads were to be found among the rows.

Newlands called this the law of octaves (there are seven notes to an octave in music, the eighth note being almost a duplicate of the first note and beginning a new octave.) Unfortunately, while some of the rows in his table did contain similar elements, other rows contained widely dissimilar elements. It was felt by other chemists that what Newlands was demonstrating was coincidence rather than something of significance. He failed to get his work published.

Two years earlier, a French geologist, Alexandre Emile Beguyer de Chancourtois (1820-1886) had also arranged elements in order of increasing atomic weight and had plotted them on a sort of cylindrical graph. Here, too, similar elements tended to fall into vertical columns. He published his paper, but not his graph, and his work went unnoticed, also.

More successful was the German chemist Julius Lothar Meyer (1830-1895). Meyer considered the volume taken up by certain fixed weights of the various elements. Under such conditions, each weight contained the same number of atoms of its particular element. This meant that the ratio of the volumes of the various elements was equal to the ratio of the volumes of single atoms of the various elements. Therefore, one could speak of atomic volumes.

If the atomic volumes of the elements were plotted against the atomic weight, a series of waves was produced, rising to sharp peaks at the alkali metals: sodium, potassium, rubidium, and cesium. Each fall and rise to a peak corresponded to a period in the table of elements. In each period a number of physical properties other than atomic volume also fell and rose.

Hydrogen, the first in the list of elements (it has the lowest atomic weight) is a special case and can be considered as making up the first period all by itself. The second and third period in Meyer's table included seven elements each, and duplicated Newlands's law of octaves. However, the two waves following included more than seven elements, and this clearly showed where Newlands had made his mistake. One could not force the law of octaves to hold strictly throughout the table of elements, with seven elements in each row. The later periods had to be longer than the earlier periods.

Meyer published his work in 1870, but he was too late. The year before, a Russian chemist, Dmitri Ivanovich Mendeleev (1834-1907), had also discovered the change in length of the periods of elements, and then went on to demonstrate the consequences in a particularly dramatic fashion.

Mendeleev was taking his graduate work in Germany at the time of the Karlsruhe Congress, and he was one of those who attended and heard Cannizzaro express his views on atomic weight. After his return to Russia, he, too, began to study the list of elements in order of increasing atomic weight.

Mendeleev tackled matters from the direction of valence. He noted that the earlier elements in the list showed a progressive change in valence. That is, hydrogen had a valence of 1, lithium of 1, beryllium of 2, boron of 3, carbon of 4, nitrogen of 3 (5), sulfur of 2 (6), fluorine of 1 (7), sodium of 1, magnesium of 2, aluminum of 3, silicon of 4, phosphorus of 3 (5), oxygen of 2 (6), chlorine of 1 (7), and so on.

Valence rose and fell, establishing periods; first, hydrogen itself; then two periods of seven elements each; then periods containing more than seven elements. Mendeleev used his information to prepare not merely a graph, as Meyer and Beguyer de Chancourtois, had, but a table like that of Newlands.

Such a periodic table of the elements was clearer and more dramatic than a graph, and Mendeleev avoided Newlands's mistake of insisting on equal periods throughout.

Mendeleev published his table in 1869, the year before Meyer published his work. However, the reason the lion's share of the credit for the discovery of the periodic table is accorded to him over the other contributions is not a mere matter of priority of publication. It rests instead on the dramatic use to which Mendeleev put his table.

In order to make the elements fit the requirements that those in a particular column all have the same valence, Mendeleev was forced in one or two cases to put an element of slightly higher atomic weight ahead of one of slightly lower atomic weight. This, tellurium (atomic weight 127.6, valence 2) had to be put ahead of iodine (atomic weight 126.9, valence 1) in order to keep tellurium in the valence-2 column and iodine in the valence-1 column.

(His instinct in this respect led him in the correct direction, though the reason for it wasn't made clear for nearly half a century)

As if this were not enough, he also found it necessary to leave gaps altogether in his table. Rather than considering these gaps as imperfections in the table, Mendeleev seized upon them boldly as representing elements as yet undiscovered.

In 1871, he pointed to three gaps in particular, those falling next to the elements boron, aluminum, and silicon in the table as modified in that year. He went so far as to give names to the unknown elements that he insisted belonged in those gaps; eka-boron, eka-aluminum, and eka-silicon ("eka" is the Sanskrit word for "one"). He also predicted various properties of these missing elements, judging what these must be from the properties of the elements above and below the gaps in his table - thus following and completing the insight of Dobereiner.

The world of chemistry remained skeptical and would perhaps have continued so if Mendeleev's bold predictions had not been dramatically verified. That this happened was due, first of all, to use of a new chemical tool - the spectroscope.

Filling the Gaps

In 1814, a German optician, Joseph von Fraunhofer (1787-1826), was testing the excellent prisms he manufactured. He allowed light to pass first through a slit and then through his triangular glass prisms. The light, he found, formed a spectrum of color that was crossed by a series of dark lines. He counted some six hundred of these lines, carefully noting their positions.

These lines were made to yield startling information, in the late 1850's, by the German physicist Gustav Robert Kirchhoff (1824-1887), working with the German chemist Robert Wilhelm Bunsen (1811-1899).
The basic source of light they used was a Bunsen burner, invented by Bunsen and known to every beginning student in a chemistry laboratory down to this day. This device burns a mixture of gas and air to produce a hot, scarcely luminous flame. When Kirchhoff placed crystals of various chemicals in the flame, it glowed with light of particular colors. If this light was passed through a prism it separated into bright lines.

Each element, Kirchhoff showed, produced a characteristic pattern of bright lines when heated to incandescence, a pattern different from that of any other element. Kirchhoff had this worked out a method of "fingerprinting" each element by the light it produced when heated. Once the elements had been fingerprinted, he could work backward and deduce the elements in an unknown crystal from the bright lines in its spectrum. The device used to analyze elements in this fashion was named the spectroscope.

As we know today, light is produced as a result of certain events that occur within the atom. In each type of atom these events occur in a particular manner. Therefore, each element will emit light of certain wavelengths and no others.

Light falls upon vapor, those same events within the atoms of the vapor can be made to occur in reverse. Light of certain wavelengths is then absorbed rather then emitted. What's more, since the same events are involved in either case (forward in one case, backward in the other), the wavelengths of light absorbed by vapor under one set of conditions are exactly the same as those that particular vapor would emit under another set of conditions.

The dark lines in the spectrum of sunlight were produced, it seemed very likely, by absorption of the light of the glowing body of the sun by the gases of its relatively cool atmosphere. The vapors in the sun's atmosphere absorbed light, and from the position of the resulting dark lines in the spectrum one could tell what elements were present in the sun's atmosphere.

The spectroscope was used to show that the sun (and the stars) was made up of elements identical with those on the earth. This conclusion finally exploded Aristotle's belief that the heavenly bodies consisted of substances distinct in nature from those making up the earth.

The spectroscope offered a new and powerful method for detecting new elements. If a mineral brought to incandescence should reveal spectral lines belonging to no known element, it seemed reasonable to suppose that an unknown element was involved.

Bunsen and Kirchhoff proved this supposition handily when, in 1860, they tested a mineral with strange spectral lines and began to search it for a new element. They found the element and proved it to be an alkali metal, related in properties to sodium and potassium. They named it cesium, from a Lain word meaning "sky blue", for the color of the most prominent line in its spectrum. In 1861, they repeated their triumph by discovering still another alkali metal, rubidium, from a Latin word for red, again from the color of a spectral line.

Other chemists began to make use of this new tool. One of them was the French chemist Paul Emile Lecoq de Boisbaudran (1838-1912), who spent fifteen years studying the minerals of his native Pyrenees by means of the spectroscope. In 1875, he tracked down some unknown lines and found a new element in zinc ore. He named it gallium, for Gaul (France).

Sometimes afterwards, he prepared enough of the new element to study its properties. Mendeleev read Lecoq de Boisbaudran's report and at once pointed out that the new element was none other than his own eka-aluminum. Further investigation made the identification certain; Mendeleev's prediction of the properties of eka-aluminum matched those of gallium in every respect.

The other two elements predicted by Mendeleev were found by older techniques. In 1879, a Swedish chemist, Lars Fredrick Nilson (1840-1899), discovered a new element he called scandium (for Scandinavia). When its properties were reported, one of Nilson's colleagues, the Swedish chemist Per Theodor Cleve (1840-1905), at once pointed out its similarity to Mendeleev's description of eka-boron.
Finally, in 1886, a German chemist, Clemens Alexander Winkler (1838-1904), analyzing a silver ore, found that all the known elements it contained amounted to only 93 per cent of its weight. Tracking down the remaining 7 per cent, he found a new element he called germanium (for Germany). This turned out to be Mendeleev's eka-silicon.

Thus, within fifteen years of Mendeleev's description of three missing elements, all three had been discovered and found to match his descriptions with amazing closeness. No one could doubt thereafter the validity or usefulness of the periodic table.

New Elements by Groups

Mendeleev's system had to withstand the impact of the discovery of still additional new elements, for which room might, or might not, be found in the periodic table.

As far back as 1794 a Finnish chemist, Johan Gadolin (1760-1852), had discovered a new metallic oxide (or earth) in a mineral obtained from the Ytterby quarry near Stockholm, Sweden. Because the new earth was much less common than such other earths as silica, lime, and magnesia, it was referred to as a rare earth. Gadolin named his oxide yttria after the quarry; fifty years later, it yielded the element yttrium. The rare earth minerals were analyzed during the mid-nineteenth century and were found to contain an entire group of new elements, the rare earth elements. The Swedish chemist Carl Gustav Mosander (1797-1858) discovered no fewer than four rare earth elements in the late 1830's and early 1840's. These were lanthanum, erbium, terbium, and didymium. Actually, five were involved, for forty years later, in 1885, the Austrian chemist Carl Auer, Baron von Welsbach (1858-1929), found that didymium was a mixture of two elements, which he called praseodymium and neodymium. Lecoq de Boisbaudran discovered two others, samarium, in 1879, and dysprosium, in 1886. Cleve also discovered two: holmium and thulium, both in 1879. By 1907 when a French chemist, Georges Urbain (1872-1938), discovered the rare earth element lutetium, fourteen such elements in all had been discovered.

The rare earths possessed very similar chemical properties, and all had a valence of 3. One might suppose this meant they would all fall into a single column of the periodic table. Such an ordering was impossible. No column was long enough to hold fourteen elements. Besides, the fourteen rare earth elements had a very closely spaced set of atomic weights. On the basis of the atomic weights they all had to be placed in a single horizontal row - in one period, in other words. Room could be made for them in the sixth period provided that period were assumed to be longer than the fourth and fifth periods, just as those were longer than the second and third. The similarity in properties of the rare earth elements went unexplained until the 1920's. Until then, the lack of explanation cast a shadow over the periodic table.

Another group of elements whose existence was completely unsuspected in Mendeleev's time caused no such trouble. Indeed, they fit into the periodic table quite well.

Knowledge concerning them began with the work of the English physicist John William Strutt, Lord Rayleigh (1842-1919), who, in the 1880's, was working out with great care the atomic weights of oxygen, hydrogen, and nitrogen. In the case of nitrogen he found that the atomic weight varied according to the source of the gas. Nitrogen from the air seemed to have a slightly higher atomic weight than nitrogen from chemicals in the soil.

A Scottish chemist, William Ramsay (1852-1916), grew interested in this problem and recalled that Cavendish, in a long-neglected experiment, had tried to combine the nitrogen of the air with oxygen. He had found that a final bubble of gas was left over which could not be made to combine with oxygen in any circumstances. That final bubble, then, could not have been nitrogen. Could it be that nitrogen, as ordinarily extracted from air, contained another gas, slightly denser then nitrogen, as an impurity, and that it was that gas which made nitrogen from air seem a little heavier than it ought to be?

In 1894, Ramsay repeated Cavendish's experiment and then applied an analytical instrument Cavendish had not possessed. Ramsay heated the final bubble of gas which would not react and studied the bright line of its spectrum. The strongest lines were in positions that fitted those of no known element. The final bubble was a new gas denser than nitrogen and making up about 1 per cent of the volume of the atmosphere. It was chemically inert and could not be made to react with any other element, so it was named argon, from a Greek word meaning "inert".

Argon proved to have an atomic weight of just under 40. This meant that it would have to fit into the periodic table somewhere in the region of the following elements: sulfur (atomic weight 32), chlorine (atomic weight 35.5), potassium (atomic weight 39), and calcium (atomic weight, just over 40).
If the atomic weight of argon were the only thing to be considered, the new element would have to go between potassium and calcium. However, Mendeleev had established the principle that valence was more important than atomic weight. Since argon combined with no element, it could be said to have a valence of 0. How did that fit?

The valence of sulfur is 2, that of chlorine 1, that of potassium 1, and that of calcium 2. The progression of valence in that region of the periodic table is 2,1,1,2. A valence of 0 would fit neatly between the two 1's: 2,1,0,1,2. Therefore argon was placed between chlorine and potassium.

However, if the periodic table was to be accepted as a guide, argon could not exist alone. It had to be one of a family of inert gases, each with a valence of 0. Such a family would fit neatly between the column containing the halogens (chlorine, bromine, iodine, etc.) and that containing the alkali metals (sodium, potassium, etc.), each with a valence of 1.

Ramsay began the search. In 1895, he learned that in the United States samples of gas (that had been taken from nitrogen) had been obtained from a uranium mineral. Ramsay repeated the work and found that the gas, when tested spectroscopically, showed lines that belonged neither to nitrogen nor argon. Instead, most astonishingly, they were the lines that had been observed in the solar spectrum by the French astronomer Pierre Jules Cesar Janssen (1824-1907) during a solar eclipse in 1868. At the time, the English astronomer Joseph Norman Lockyer (1836-1920) had attributed them to a new element which he had named helium, from a Greek work for sun.

On the whole, chemists had paid little attention at that time to a discovery of an unknown element in the sun based on evidence as fragile as a spectral line. But Ramsay's work showed the same element to exist on the earth, and he retained Lockyer's name. Helium is the lightest of the inert gases and, next to hydrogen, the element with the lowest atomic weight.

In 1898, Ramsay carefully boiled liquid air, looking for samples of inert gases that he expected to bubble off first. He found three, which he named neon ("new"), krypton ("hidden"), and xenon ("stranger").
The inert gases were at first considered mere curiosities, of interest only to the ivory-tower chemists. In researches beginning in 1910, however, the French chemist Georges Claude (1870-1960) showed that an electric current forced through certain gases such as neon produced a soft, colored light.

Tubes filled with such gas could be twisted into multi-colored letters of the alphabet, words, and designs. By the 1940's the incandescent light bulbs of new York City's celebrated Great White Way and similar centers of festivity had been replaced with neon lights.