CHAPTER # 1 INTRODUCTION OF CHEMISTRY
Qno1. What is Chemistry?
Ans: Chemistry is the branch of science which deals the study of properties, composition and structure of matter along.
Qno2. Shortly Define the importance of Chemistry in our society?
Ans: There are lots of Importance of chemistry in our society like,
1. Drugs to resistance for disease.
2. Fibers to provide comfort.
3. Fuels for transportation
4. Pesticides to protect our health and crops.
5. Chemistry also helps us to understand the nature of our environment and about ourselves.
6. At the oil refinery, crude oil is converted into chemicals which can be used in products such as fuels (Petrol, Diesel, Kerosene), Plastics, cosmetics, drugs, paints and detergents.
7. The chemist has helped by producing fertilizers, insecticides, pesticides, etc. which increase the crop yield and help to make farming more efficient.
Qno3. Describe the Historical development of Chemistry?
Ans: There are three periods of development of chemistry.
1. The Greek Period
2. The Muslim Period
3. The Modern Period
1. The Greek Period
The Greek Philosophers Plato, Aristotle, Democritus, Empedocles, etc., believed in the concept of four elements on earth. These elements were fire, air, earth and water. They also believed that these elements were not interconvertible. Greek period was mostly the age of theoretical science while chemistry is basically a practical science. Therefore, chemistry could not make much progress in the Greek period.
2. The Muslim Period
The Muslim period extends from 600 to 1600 AD. It is also known as the period of alchemists. The Muslim scientists made great contributions to the various branches of science especially in the fild of chemistry.
Contribution of Muslim Scientist
Jabir Ibne Haiyan: He prepared nitric Acid (HNO3), Sulphuric acid (H2SO4) and white lead. He developed methods for the extraction of metals form their ores and dyeing cloth. He is generally known as the father of alchemy.
Al-Razi: He was an expert surgeon. He used Opium as an anesthesia for the first time. He prepared ethyl alcohol for the first time. He divided the substances into living and nonliving origins. He was a physician, alchemist and a philosopher.
Al Beruni: His contribution was made in physics, metaphysics, geography, history and mathematics, He determined the densities of different substances.
Ibne - Sina: He made contribution in the field of medicines, medicinal chemistry, philosophy, mathematics and astronomy.
3. The Modern Period:
In this period the following scientist working day and night for the progress of chemistry and other science.
Robert Boyle: He is known as the father of modern chemistry.
J. Black: He discovered carbon dioxide.
J. Priestley: He discovered oxygen, sulphur dioxide and hydrogen
chloride.
Scheele: He discovered chlorine.
Cavendish: He discovered hydrogen.
Lavoisier: He discovered that oxygen is one fifth of the air.
John Dalton: He proposed the atomic theory of matter.
J.J Berzellius: He used symbols, formula and chemical equations in
chemistry.
Mendeleef: He discovered the periodic arrangements of elements.
Michael Faraday: He put forward the laws of electrolysis.
Arrhenius: He put forward the ionic theory.
In addition to these, Gay Lussac, Avogadro, Dulang, Petit, J.J Thomson, He Becquerel, Madam Curie, Neil Bohr and E. Rutherford Contributed to the filed of chemistry by their work.
Qno4. What important role chemistry plays in the society?
Ans: Chemistry and Society:
Chemistry affects all aspects of our lives, it has important practical applications in the society, it provides us food with the use of fertilizers, insecticides, pesticides and preservatives to store food for a log time, it provides us with cloth by making polymers and other synthetic fibers. It provides us with a number of other materials such as concrete, glass, plastic, fuel and of course medicines, these materials and mused in the making of buildings household things for moving our vehicles and protecting us from diseases and prolonging our lives in addition to making outlives more enjoyable, more luxurious and more comfortable.
Many Chemicals are used so extensively in our daily lives. For example, chlorine is used to make more than one thousand compounds, from which pipes, bleaching agents, disinfectants, solvents, pesticides, refrigerants, flame retardants, drugs, etc, are made chlorine is universally used to kill all pathogens of water borne diseases that is why all water supplies and reservoirs are treated with chlorine so that water can become safe from harmful pathogens.
Qno5. Name the difference branches of chemistry and define them?
Ans: From Book
Qno6. What do you mean by scientific approach in chemistry?
Ans. Scientific approach:
It includes the following four steps:
1. Observation: The basic tools of observation for a man are his own five senses. Scientific equipment are also used for making observations. Information acquired through careful observation is called fact. These facts serve as the foundation of the scientific approach in chemistry.
2. Hypothesis: When the observation has been made, the scientist ponders over it. It is simply a guess. A hypothesis is an “intelligent guess” aimed at explaining “how” or Why” something happens. A hypothesis is a tentative solution to explain an observed phenomenon.
3. Theory: The hypothesis is then tested through experiments. These experiments are performed under a variety of conditions either to confirm or deny the hypothesis. If the Hypothesis is supported by different experiments. It becomes a theory. A good theory predicts new facts. If a hypothesis does not hold true. It is either modified or rejected.
Qno7. How will you differentiate between hypothesis and theory?
Ans: Difference between hypothesis and theory:
A hypothesis is an intelligent guess which is made on the basis of observation. A hypothesis provides tentative solution to the observed phenomenon. A theory is a tested hypothesis. A hypothesis is tested by making experiments. If the same results are obtained from the experiments made in variety conditions, then a hypothesis gets the status of a theory, Both hypothesis and theory are tentative, they may be modified or ultimately discarded if they do not pass all the tests successfully in a wide series of experiments.
Qno8. What is scientific Law?
Ans: Scientific Law:
A theory which repeatedly give the same results after experimentation and offers correct explanation of scientific facts is called a scientific law or principle.
CHAPTER # 2 CHEMICAL COMBINATION
Qno1. State the Law of conservation of mass?
Ans. Law of conservation of mass:
Antoine lavoisier, a French chemist, stated the law of conservation of mass in 1785:
Statement:
“Conservation of mass: a fundamental principle of classical physics that matter cannot be created or destroyed in an isolated system.”
Or
“The total mass of the reacting substances (the reactants) is equal to the total mass of the products of a chemical reaction. Matter cannot be created or destroyed during chemical reactions.
Example:
1. The weight of iron increases on rusting. The Increase in weight is equal to the weight of oxygen added to iron.
2. Water forms by the union of hydrogen and oxygen. If we weigh the reactants (hydrogen and oxygen) before the reaction, we find the weigh of the product (water)
equal to the combined weight of reactants.
Qno2. Describe Landolt experiment for practical verification of law of conservation of
mass.
Landolt Experiment:
H. Landolt was German Chemist. He proved the law of conservation of mass by using an H-shaped glass tube. he filled silver nitrate in limb A and hydrochloric acid in limb B. The tube was sealed and weighed before the chemical reaction. The reactants were mixed by inverting and shaking the tube. A white precipitate of silver chloride was formed along with nitric acid. The tube was weighed again. He found that there was no change in weight during the following chemical reaction.
H. Landolt was German Chemist. He proved the law of conservation of mass by using an H-shaped glass tube. he filled silver nitrate in limb A and hydrochloric acid in limb B. The tube was sealed and weighed before the chemical reaction. The reactants were mixed by inverting and shaking the tube. A white precipitate of silver chloride was formed along with nitric acid. The tube was weighed again. He found that there was no change in weight during the following chemical reaction.
Qno3. State the law of definite/constant propotions in your own words:
Ans. Law of Definite/constant Proportion:
This observation was first made by the French chemist Louis Proust, based on several experiments conducted between 1799 and 1804.[2] Based on such observations, Proust made statements like this one, in 1806:
Statement:
In chemistry, the law of definite proportions, sometimes called Proust's Law, states that a chemical compound always contains exactly the same proportion of elements by mass. An equivalent statement is the law of constant composition, which states that all samples of a given chemical compound have the same elemental composition.
Example:
1. Pure water, either prepared in the laboratory or obtained from rain, river, sea ocean, well, water pump, etc. contains one part hydrogen and eight parts oxygen by mass.
2. Berzelius heater 10g of lead with various amounts of sulphur. He got exactly 11.56g lead sulphur and the excess of sulphur was left over. When be heated 18g lead with 1.56g sulphur, he got exactly 11.56 lead Sulphide and 8g lead was left over.
Qno4. What is law of multiple Proportion? Explain with example?
Law of multiple Proportion:
In chemistry, the law of multiple proportions is one of the basic laws of stoichiometry, alongside the law of definite proportions. It is sometimes called Dalton
Statement:
If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers.
Example:
The law of multiple proportions is best demonstrated using simple compounds. For example, if one tried to demonstrate it using the hydrocarbons decane (chemical formula C10H22) and undecane (C11H24), one would find that 100 grams of carbon could react with 18.46 grams of hydrogen to produce decane or with 18.31 grams of hydrogen to produce undecane, for a ratio of hydrogen masses of 121:120, which is hardly a ratio of "small" whole numbers.
Qno5. State the law of reciprocal proportions and illustrate it with examples.
Ans: Law of Reciprocal Proportions:
This law was enunciated by Ritcher in 1792-94. It states that "when two different elements separately combine with the fixed mass of third element, the proportion in which they combine with one another shall be either in the same ratio or some simple multiple of it".
Example:
When two elements C and O separately combine with H to form methane (CH4) and water (H2O) respectively it is very clear that in methane 3g of C with 1g of hydrogen, and in water (H2O) 8g of O with the same (fixed) mass i.e (1g) of H. Now when C and O combine with each other to form carbon dioxide (CO2), they do so in the same proportion i.e. 12:32 = 3:8 parts by mass.
Qno6. What is atomic Mass?
Atomic Mass:
Definition:
Atomic mass or atomic weight is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. Also Known As, “Atomic Weight”
Examples: The atomic mass of carbon is 12.011; the atomic mass of hydrogen is 1.0079
Qno7. What is atomic Mass Unit?
Ans: Atomic Mass Unit (a.m.u)
Mostly chemists use relative comparisons of the masses of atoms. The unit of comparison is the atomic mass unit (a.m.u)
Definition:
An atomic mass unit (symbolized AMU or amu) is defined as precisely 1/12 the mass of an atom of carbon-12. The carbon-12 (C-12) atom has six protons and six neutrons in its nucleus.
Qno8. What is empirical Formula? Give examples.
Ans: Empirical formula:
Definition:
A chemical formula that indicates the relative proportions of the elements in a molecule rather than the actual number of atoms of the elements. The empirical formula of a compound may be simpler than its molecular formula, which is a multiple of the empirical formula.
Example:
1. Glucose has the molecular formula C6H12O6 but the empirical formula CH2O.
2. The Molecular formula of Benzene is C6H6 the ratio of Carbon to hydrogen is 6:6 or 1:1 the empirical formula of benzene is CH.
Qno9. What is Molecular Formula? Give example:
Ans: Molecular Formula:
Definition:
“Molecular formula of an element or a compound shows the actual number of atoms present in the molecules of these substances.”
A molecular formula may be the same as empirical formula e.g. water (H2O), carbon dioxide (CO2) have got the same molecular and empirical formulas.
Or a molecular formula may be a simple whole number multiple of an empirical
formula.
Molecular Formula = (Empirical Formula )x n
n = 
Example:
Compound Molecular Formula
Carbon dioxide CO2
Sugar C12H22O11
Glucose C6H12O6
Hydrogen Peroxide H2O2
Qno10. What is Molecular Formula mass?
Ans: Molecular Formula Mass:
Definition:
“It is the sum of the atomic masses of all the atoms present in the molecular formula of a substance or molecule.”
Example:
Molecular formula mass of CO2
Atomic mass of Carbon = C = 12 a.m.u
Atomic mass of Oxygen = O = 16 a.m.u
Therefore,
CO2 = 12 + 16x2
CO2 = 12 + 32 CO2 = 44 a.m.u
Qno11. Define formula Mass?
Ans. Formula Mass:
Definition:
It is the sum of the atomic masses of all atoms in a formula unit of the Substance.
Example
The formula mass of sodium Chloride NaCl is
1 Na = 1x23 = 23.0 a.m.u
1 Cl = 1x35.5 = 35.5 a.m.u
Formula Mass of NaCl = 58.5 a.m.u
The term formula mass can be applied to both molecular mass and ionic mass.
Qno13. Define molar mass. Give example:
Ans: Molar Mass
Definition:
Molar mass of a substance is its atomic, molecular formula, or formula mass expressed in
grams.
grams.
e.g Molar mass of C = 12g
Molar mass of ammonia (NH3)=
1 N = 1 x 14 = 14g
3 H = 3 x 1 = 3g
Molar mass of NH3 = 17g
Therefore, Mass of one mole of substance is called its molar mass. It is express in grams.
Qno14. Define mole? Give example.
Ans. Mole
Definition:
A mole is define as the amount of substance, which contains the Avogadro number of particles. The value of Avogardro number is 6.02 x 1023.
One mole of atoms contains 6.02 x 1023 atoms. One mole of molecules contains 6.02 x 1023 molecules. One mole of formula units contains 6.02 x 1023 formula units. One mole of ions contains 6.02 x 1023 ions.
Mole is also define as the atomic mass, molecular mass or formula mass of a substance expressed in grams.
Thus 1 mole of C = 12g
1 mole of H2O = 18g
1 mole of NaCl = 58.5 g
Formula of Mole:
Mole = 
Qno15. Define Avogadro’s Number and write its uses.
Ans. Avogadro Number:
Definition:
The Avogadro number is defined as the number of representative Particles (atoms, ions,
molecules)
Present in one mole of substance. Avogadro number is represented by NA. it has a fixed value of 6.02 x 1023
Uses of Avogadro’s Number:
1. It is used to calculate the number of atoms or molecular in a given sample of substance.
2. It is used to calculate the mass of a single atom or molecule of a substance.
Qno16. What is a chemical reaction? Name the type of chemical reactions and define
them?
Ans. Chemical Reaction:
Definition:
A chemical reaction is a chemical change in which the composition of a substance is changed. One or more new substances are formed from the original substance. In a chemical reaction old bonds are broken and new bonds are formed.
Type of Chemical Reaction:
Chemical reactions can be divided into five different types. They are:
1. Decomposition reactions
2. Addition Reactions (Combination Reaction)
3. Single Displacement reactions.
4. Double Displacement reactions
5. Combustion reaction.
1. Decomposition Reaction
Definition:
A reaction in which a chemical substance breaks down into two or more simple substances is called Decomposition Reaction. In a decomposition reaction, the reactant is always a compound and the product may be any combination of elements and compounds. Decomposition reactions are endothermic, they require energy for decomposition.
Example:
Calcium Carbonate decomposes into calcium oxide and carbon dioxide on heating.
CaCO3 CaO + CO22. Combination Reaction or Addition reaction:
Definition:
A reaction in which tow or more substances combine to form a single substance is called a combination reaction. A combination reaction is also called an addition reaction. It is the reverse of a decomposition reaction.
In addition reactions the product is always a compound. However, the reactions may be two elements or two compounds or an element and a compound. Addition reactions are exothermic reactions as they liberate energy.
Example:
Calcium oxide and carbon dioxide react to gather and form Calcium Carbonate.
CaO + CO2 CaCO33. Single Replacement Reaction / Displacement Reaction:
Definition:
One element displaces another element in a single replacement reaction. These reaction is also called single Replacement reaction.
Example:
A more reactive metal displaces a less reactive metal from its compound.
Fe (s) + CuO(s) Cu(s) + FeO(s)4. Double Displacement Reaction
Definition:
A reaction in which two compounds exchange their partners and form two new compound. This reaction involves an exchange of cation (or anion). These reactions usually take place in aqueous solutions between two ionic substances.
Example:
1. Sodium chloride and silver nitrate react to form sodium nitrate and silver chloride.
NaCl + Ag NO3 NaNo3 + AgCl whit PPt5. Combustion Reaction:
Definition:
A reaction in which a substance reacts with oxygen producing heat and light is called a combustion reaction.
Example:
Carbon burns in air producing carbon dioxide and heat.
C + O2 CO2 + HQno17: What is chemical equation? What is a coefficient? Give an example of a balanced equation?
Chemical Equation:
A chemical equation is a short hand way of representing a chemical reaction.
Following steps are taken in writing a chemical equation.
1. Reactants are written on the left hand side of chemical equation while products are written on the right.
2. Reactants and product are connected by an arrow.
3. Balance the equation. Balanced equation have the same kind and number or atoms on each side.
4. Indicate physical state of the reactants and products. We use (s) for solid, (l)for liquid and (g) for gas and (aq) for aqueous.
Coefficient:
A coefficient is a small whole number written in front of a symbol or formula in a chemical equation. If the coefficient is 1 , it is not written, Coefficient are used to balance chemical equation.
Example:
H2 + O2 2H2O In the above equation “2” is a Coefficient
Qno18. Define the following:
1. Chemical Reaction 2. Reactant 3. Product
Ans: Chemical Reaction:
A chemical reaction is the changing of substances to other substances by the breaking of old bonds and the formation of new bonds.
Reactant:
Reactants are the initial substances in a chemical reaction. They are written on the left side of the chemical equation along with their physical state. After a chemical reaction, the reactants are changed into products.
Products:
Products are the resulting substances in a chemical reaction. They are written on the right side of the chemical equations along with their physical state.
Qno1. Write down the main point of Dalton Atomic Theory?
Ans. Dalton
In 1808, john Dalton
theory.
“Dalton
This theory of atomic
Composition was hypothesized and partially confirmed by the English chemist and Physicist John Dalton.” The main point of this theory is given below.
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds
of atoms.
4) A chemical reaction is a rearrangement of atoms.
Qno2. Discuss Rutherford ’s gold metal foil experiment? What did it tell about the
structure of the atoms?
Ans. Rutherford ’s Gold foil Experiment:
Ernest Rutherford, a New Zealander, designed an experiment to study how alpha particles, with a 2+ charge, interact with a piece of very thin gold foil. Rutherford bombarded a very thin piece of gold foil with a stream of positively charged particles known as the alpha particles.
Observation:
1. He observed that most of the alpha particles were pass through the foil
undeflected.
2. Very few particles were deflected when passed through the foil.
3. One particle out of 8000 particles was rebound.
Important Points of Rutherford ’s Theory:
· Major portion of the atom is empty.
· The whole mass of the atom is concentrated in the center of atom
called nucleus.
· The positively charged particles are present in the nucleus of atom.
· The charge on the nucleus of an atom is equal to (+z.e).
· The electrons revolve around the nucleus in different circular orbits.
· Size of nucleus is very small as compare to the size of atom.
Defected of Rutherford ’s Theory:
· According to electromagnetic theory, being a charge particle, a revolving electron must emit energy. Due to emission of energy, the orbit of electron will decrease. Consequently electron will fall into the nucleus. But this is against the actual situation and this shows that atom is unstable.
· If the electrons emit energy continuously, they should form continuous spectrum .But actually line spectrum is obtained
Qno3. Write in detail main features of Bohr’s theory?
Ans. Bohr’s Atomic Theory:
Neil Bohr removed the defect in Rutherford ’s atomic model. He was presented his Atomic theory in 1913.
The Main Features of Bohr’s Theory are given below:
CONSTANT ENERGY CONCEPT:
Energy of an electron is constant in one of its allowed orbits. As long as an electron remains in its orbit, it neither absorbs nor radiates energy.
CONCEPT OF ENERGY LEVELS:
Electrons revolve around the nucleus of atom in circular orbits in which energy of electrons is constant. These circular paths are known as "energy levels" or "stationary states".
RADIATION OF ENERGY
If an electron jumps form higher energy level to a lower energy level, it radiates a definite amount of energy.
ABSORPTION OF ENERGY
If an electron jumps from lower energy level to a higher energy level, it absorbs a definite amount energy.
AMOUNT OF ENERGY
Energy released or absorbed by an electron is equal to the difference of energy of two energy levels.
Let an electron jumps from a higher energy level E2 to a lower energy level E1.The energy is emitted in the form of light . Amount of energy released is given by:
ΔE = E2 - E1
E2 - E1= hυ
Where
h = Planck's constant ( 6.6256 x 10-34 j.s)
υ= Frequency of radiant light
Qno5. What is Proton and how were this Produced?
Ans. Discovery of Proton:
Since the atom is electrically neutral there must be positively charged particles present in the atom to neutralize the negative charges of the electrons. Goldstein experimentally proved the existence of protons in the atom. Goldstein (1886) found that some rays passed through these holes in a direction opposite to that of the cathode rays. J.J. Thomson (1897) measured their charge by mass ratio from which he was able to deduce that these contain positive ions. Their properties are
Properties of Positive Rays:
- Travel in straight lines: They cast a shadow of the objects placed in their way.
- Produce mechanical effect: A paddle wheel placed in their path starts rotating.
- Rays are positively charged: Anode rays are deflected towards the negative plate of an electric field.
- The nature of the anode rays depends upon the gas taken in the discharge tube. Different gases give different types of positive rays, which contain particles having different masses and different charges. Therefore the e/m ratio is not constant for positive ray particles obtained from different gases.
A proton like an electron, is the fundamental particle of an atom, which carries a unit positive charge.
Qno6. What are the Characteristic of Electron, Proton and neutron?
Ans. CHARACTERISTICS OF ELECTRON:
Charge: It is a negatively charged particle.
Magnitutide of charge: Charge of electron is 1.6022 x 10-19 coulomb.
Mass of electron: Mass of electron is 0.000548597 a.m.u. or 1.1 x 10-31 kg.
Symbol of electron: Electron is represented by "e".
Location in the atom: Electrons revolve around the nucleus of atom in different circular orbits.
Magnitutide of charge: Charge of electron is 1.6022 x 10-19 coulomb.
Mass of electron: Mass of electron is 0.000548597 a.m.u. or 1.1 x 10-31 kg.
Symbol of electron: Electron is represented by "e".
Location in the atom: Electrons revolve around the nucleus of atom in different circular orbits.
CHARACTERISTICS OF PROTON
Charge: Proton is a positively charged particle.
Magnitude of charge: Charge of proton is 1.6022 x 10-19 coulomb.
Mass of proton: Mass of proton is 1.0072766 a.m.u. or 1.6726 x 10-27 kg.
Comparative mass: Proton is 1837 times heavier than an electron.
Position in atom: Protons are present in the nucleus of atom.
Magnitude of charge: Charge of proton is 1.6022 x 10-19 coulomb.
Mass of proton: Mass of proton is 1.0072766 a.m.u. or 1.6726 x 10-27 kg.
Comparative mass: Proton is 1837 times heavier than an electron.
Position in atom: Protons are present in the nucleus of atom.
CHARACTERISTICS OF NEUTRON
Charge: It is a neutral particle because it has no charge.
Mass of neutron: Mass of neutron is 1.0086654 a.m.u. or 1.6749 x 10-27 kg.
Compartive mass: Neutron is 1842 times heavier than an electron.
Location in the atom: Neutrons are present in the nucleus of an atom.
Mass of neutron: Mass of neutron is 1.0086654 a.m.u. or 1.6749 x 10-27 kg.
Compartive mass: Neutron is 1842 times heavier than an electron.
Location in the atom: Neutrons are present in the nucleus of an atom.
Qno7. What is the proof that all atoms contain Electorn?
Ans. Electrons are obtained irrespective of the nature of the cathode or the gas inside the discharge tube. It proves that all atoms contain electron.
Qno8. What is the radioactivity? Describe the three types of rays emitted by radioactive
substance?
Ans. Radioactivity:
Unstable atomic nuclei will spontaneously decompose to form nuclei with a higher stability. The decomposition process is called radioactivity. The energy and particles which are released during the decomposition process are called radiation. When unstable nuclei decompose in nature, the process is referred to as natural radioactivity. When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity.
Types of radioactivity:
In 1902 a British Physicist Rutherford find the nature of radioactive rays There are three types of Radioactive Rays:
Alpha Rays:
1. They consist of helium nuclei.
2. They are represented by or α He42
3. They have a double positive charge (2+)
4. They deflect towards negative electric and magnetic fields.
5. Their penetration Power is low. They are easily stopped by a sheet of paper.
Beta Rays:
1. They consist of fast moving electrons.
2. They are represented by β or e0-
3. They have unit negative charge
4. they deflect towards positive electric and magnetic fields.
5. they are much more penetrating than alpha rays. They are stopped by aluminum foil or a thin piece of wood.
Gamma Rays:
1. They are electromagnetic radiations.
2. They are represented by γ.
3. They have no charge and no mass.
4. They are not deflected in the electric or magnetic fields.
5. They are ore penetrating power than alpha and beta rays. They can be stopped by several feet of concrete or several inches of lead.
Qno9. Why it is believed that the atom has mostly empty spaces.
Ans. When Rutherford bombarded a gold foil with alpha particles, most of the particles went through the foil undeflected. It is thus believed that the atom has mostly empty spaces.
Qno10. Define the following:
a. Atomic Number b. Mass Number c. Isotopes
Ans. Atomic Number:
The number of protons in the nucleus of an atom determines an element's atomic number. In other words, each element has a unique number that identifies how many protons are in one atom of that element. For example, all hydrogen atoms, and only hydrogen atoms, contain one proton and have an atomic number of 1. All carbon atoms, and only carbon atoms, contain six protons and have an atomic number of 6. Oxygen atoms contain 8 protons and have an atomic number of 8. The atomic number of an element never changes, meaning that the number of protons in the nucleus of every atom in an element is always the same.
Atomic Mass:
The total sum of the protons and neutrons in the nucleus of an atom is called the mass number. It is denoted by A. it is written as superscript on the left hand side of the chemical symbol.
Mass Number (A) = number of protons (Z) + number of neutrons (N)
Isotopes:
Isotopes are multiple forms of an element in which the number of neutrons in nuclei of the isotopes are different from each other, although each form has the same number of protons. Isotopes are useful for radiocarbon dating and investigation of reaction mechanism. An element's isotopes have the same atomic number, but different mass numbers. Some elements do not have natural isotopes. Other elements have two or more naturally occurring isotopes. Isotopes are specified by adding the mass number after the name or symbol of the element, such as carbon-12 or H-1. Certain elements have isotopes with too many or too few neutrons, making them unstable. These unstable atoms are radioactive and shed particles over time in radioactive decay.
CHAPTER # 4 PERIODICITY OF ELEMENTS
Qno1. Define the following:
a. Dobereiner’s Rule b. Periodicity c. Modern Periodic law
d. Electronegativity
Ans. Dobereiner’s Rule
A German scientist called Johann Dobereiner put forward his law of triads in 1817. Each of Dobereiner's triads was a group of three elements. The appearance and reactions of the elements in a triad were similar to each other.
Atomic masses At this time, scientists had begun to find out the relative atomic masses of the elements. Dobereiner discovered that the relative atomic mass of the middle element in each triad was close to the average of the relative atomic masses of the other two elements. This gave other scientists a clue that relative atomic masses were important when arranging the elements.
Periodicity:
The periodicity of elements means that the properties (especially chemical Properties) of elements repeat at regular intervals in the periodic table when elements are arranged in increasing order of their atomic numbers.
Modern Periodic law
The modern periodic table is also called Bohr’s long form of periodic table as it has now 18 groups instead of only B groups. However it has 7 periods instead of 12.
Application:
1. The modern periodic table is based on increasing order of the atomic number of elements.
2. The group number shows the number of valence electrons in its valence or outermost shell.
3. the period number shows the number of shells an element has in that period.
4. The periodic shows the physical state of an element.
Electronegativity:
Definition:
Electronegativity is defined as the relative tendency of an atom in a molecule to attract shared pair of electrons to itself.
Explanation:
An American chemist, Linus Pauling, calculated the electro negativities of different elements taking fluorine as a standard. He devised a scale which ranged from
Qno2. Explain Newland’s law of octave. How this law provided the larger scope for the classification of the elements?
Ans. Newland’s Classification or Newland’s Law of Octave:
In 1863, an English chemist, john Newland, stated his law of octave as, Newland arranged many of the known elements in the increasing order of their atomic masses. He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element.
He noticed that the eighth element was similar in properties to the first element, just like the eighth note in music - Western as well as Indian.
The eighth element after lithium is sodium. In many of its chemical properties it is similar to lithium. Similarly, the eighth element after sodium is potassium, whose properties are similar to sodium. The eighth element from fluorine is chlorine both of which are similar in their properties. The eighth element from nitrogen is phosphorus and both these elements are similar in properties.
Achievements of Law of Octaves
- The law of octaves was the first logical attempt to classify elements on the basis of atomic weights.
- Periodicity of elements was recognized for the first time.
Defects of Law of Octaves
- This law could be best applied, only up to the element calcium.
- Newly discovered elements could not fit into the octave structure.
- The feature of resemblance of the 8th element when arranged in increasing order of their atomic mass was not successful with heavier elements.
Qno3. What do you understand by long form of periodic table? Explain some of its application?
Ans. Long form of periodic table:
The modern periodic table is also called Bohr’s long form of periodic table as it has now 18 groups instead of only B groups. However it has 7 periods instead of 12.
Application:
1. The modern periodic table is based on increasing order of the atomic number of elements.
2. The group number shows the number of valence electrons in its valence or outermost shell.
3. the period number shows the number of shells an element has in that period.
4. The periodic shows the physical state of an element.
Qno4. How does the modern periodic law differ from Mendeleev’s periodic law?
An.s Modern periodic law states that properties of elements are the periodic function of their atomic numbers. It has 18 groups including both A and B groups and 7 periods. Mendeleev’s periodic law stated that properties of elements are the periodic functions of their atomic masses. It had 8 groups and 12 periods.
Qno5. What do you understand by the periodic classification of elements? What are the merits and demerits of the classification of the elements in the periodic tabular form?
Ans. Periodic Classification of elements follows the periodic law which states
“Properties of the elements are the periodic functions of their atomic numbers”
The Periodic table is a classification of the elements and it can be used to predict the properties of elements. There are at present 109 known elements. The number of elements is increasing because new artificial atoms are being produced inside reactions, by nuclear reactions. The merit of classification is that elements having similar physical and chemical properties have been put together.
The physical properties include the appearance, state, density, color, smell, melting point, boiling point, boiling point, etc. By chemical properties, we mean the way the elements can react with other elements. The classification by properties divides elements into families or groups.
Qno6. Discuss the following:
a. Ionization Energy b. Electron Affinity c. Atomic Radii
Ans. Ionization Energy:
It can be defined as being the energy required to remove the outermost electron from a gaseous atom. A "gaseous atom" means an atom that is all by itself, not hooked up to others in a solid or a liquid. When enough energy is added to an atom the outermost electron can use that energy to pull away from the nucleus completely leaving behind a positively charged ion. That is why it's called ionization, one of the things formed in the process is an ion. The ionization energy is the exact quantity of energy that it takes to remove the outermost electron from the atom.
If the ionization energy is high, that means it takes a lot of energy to remove the outermost electron. If the ionization energy is low, that means it takes only a small amount of energy to remove the outermost electron.
Electron Affinity
The electron affinity of an element is the energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion. A fluorine atom in the gas phase, for example, gives off energy when it gains an electron to form a fluoride ion.
Electron affinities are more difficult to measure than ionization energies and are usually known to fewer significant figures.
Atomic Radii
An atom does not have strictly defined boundaries. The radius of a particular atom is not constant. Its size is influenced by the other atom or atoms to which it is bonded.
Definition:
Atomic radius is half the distance between the nuclei of two similar atoms which are in touch with each other.
The atomic radius depends on the number of shells and nuclear charge on an atom. It is measured in angstrom A0.
Qno7. What do you understand by representative and transition elements?
Ans. Two common classification of elements are used on the basis of what orbitals are
being filled.
Representative Elements:
They are main group, group A elements from IA to VIIIA. These are the elements which s and p orbitals are being filled.
Transition Elements:
They are subgroup, group B elements from IB to VIIIB. These are the elements in which d and f orbitals are being filled.
Qno8. Define Metals, Non – Metals and metalloids?
Ans. Metals:
A substance with high electrical conductivity, luster, and malleability, which readily loses electrons to form positive ions (cations). Metals are otherwise defined according to their position on the Periodic Table, including groupings as alkali metals, alkaline earth metals, transition metals, and rare earth metals.
Examples of Metals
Most of the elements on the periodic table are metals, including gold, silver, platinum, mercury, uranium, aluminum, sodium and calcium. Alloys, such as brass and bronze, also are metals.
Non – Metals
They are bad conductor of heat and electricity. Most of them are gases. In The periodic table, majority of elements of p-block (groups IIIA,IVA ,VA
Metalloids:
They show the properties of both metals and nonmetals. Their oxides are amphoteric.
They have basic as well as acidic properties. There are only 8 metalloids: Boron (B), Silicon (Si),Germanium (Ge), Arsenic (As) and Antimony (Sb), Selenium (Se),Tellurium (Te), Astatine (At)
Qno9. State Mendeleev's Periodic law. Describe Mendeleev's periodic table. Write down the advantages and disadvantages of Mendeleev's periodic table?
Ans. Mendeleev's Periodic law:
In 1869, a Russian chemist, Dimitri mendeleev, arranged elements in the order of increasing atomic masses, placing similar elements one below the other in vertical columns or groups and put forward his periodic law which states that "the physical and chemical properties of elements are a periodic function of their atomic weights."
Mendeleev's Periodic Table:
The salient features of Mendeleev's periodic table are given below:
1. It had 8 vertical columns or groups and 12 horizontal rows or periods.
2. The elements in each group had similar chemical properties but their physical properties changed gradually.
3. Mendeleev's Kept vacant spaces for the elements undiscovered by then. He predicted their names as Eka Boron, Eka Aluminum and Eka Silicon.
4. The group number shows the maximum number of valence electrons of its elements.
Advantages of Periodic Table:
1. The study of one element of a group helps to know the properties of other elements of the same group.
2. It helped in the discovered of elements as Mendeleev predicted about them. They were named as scandium (Sc) gallium (Ga) and germanium (Ge).
3. It helped in the correction of many doubtful atomic masses and thus elements were placed correctly in the periodic table.
Disadvantages of Periodic Table:
1. Some elements of higher atomic masses were placed before elements of lower atomic masses, e.g.
a. Ar (40) Placed before K(39)
b. Co(59.9) placed before Ni (58.6)
c. Te (127.6) placed before I (126.9)
2. There were no places for isotopes of elements.
3. Similar elements were placed in different groups.
4. Dissimilar elements were placed in the same groups.
5. It failed to tell about the atomic structure.
Qno10. Explain Clearly the periods and groups in the modern periodic
table?
Ans. Learn by heart from book.
