GOVT.

PILOT HIGHER SECONDARY SCHOOL LARKANA

Chemistry Notes By: Dildar Ali Chandio (M.Sc Chemistry)

Chapter: 01
FUNDAMENTALS OF CHEMISTRY
Q.01: What is meant by science?

Ans: The word science is derived from a latin word “scientia” which means knowledge. It is defined as the name
systematic knowledge that can obtain though observation and experiment.

Q.02: Describe the historical background of chemistry?

Ans: The development of chemistry can be divided into the following three periods.

1. The great period 2. The Muslim Period 3. The Modern Period

1. THE GREEK PERIOD

The Greek period was from 500 to 600 B.C. in the history of chemistry and is known at the period of Greeks.
Following are the prominent Greek Philosophers.

ARISTOTLE (322-384 B.C)

He proposed an idea of a substance as a combination of matter. Describes theory of the four elements i.e.
fire, water, earth, and air.

PLATO (347-428 B.C)

He proposed the term ‘elements’ as composition of organic and inorganic bodies with particular shapes.

DEMOCRITUS (370-460 B.C)

He proposed that atom is the indivisible particle of matter.

2. THE MUSLIM PERIOD

The Muslim period was from 600 to 1600 A.D. in the history of chemistry and is known as the period of
alchemist. Following are the prominent Muslim scientists.
JABIR IBNE-HAIYAN (721-815 A.D)
 He invented the experimental methods for the preparation of nitric acid, hydrochloric acid and white
lead.
 He developed methods for the extraction of metals (metallurgical techniques) and the methods of dyeing
of cloths.
 KITAB UL KAMYA is the famous book written by Jabir Ibne-Haiyan.
MUHAMMAD IBNE ZAKARIA AL RAZI (862-930 A.D)
 He prepared ethyl alcohol by fermentation process.
 He was the first who used opium as anesthesia.
 He divided the substances on the basis of living and non-living things.

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 AL-BERUNI (973-1048 A.D)
 He determined the densities of various precious stones and metals.
 Kitab-al-Qanoon ul Masoodi is the famous book written by Ibne Sina.
IBNE SINA (980-1037 A.D)
 He contributed in the field of medicine, medical chemistry, philosophy & astronomy.
 Kitab-al-Shifa is the famous book written by Ibne Sina.

3. THE MODERN PERIOD

ROBERT BOYLE (1627-1691 A.D)
 Robert Boyle put forward the idea that chemistry should be regarded as systematic
investigation of nature.
 His major contribution in the field of chemistry that he put forward gas laws.
J.BACK (1728-1799 A.D)
J. Black studied the chemistry of carbon dioxide (CO2)

J.PRIESTLEY (1733-1804 A.D)

J. Priestley discovered oxygen, sulphur dioxide and hydrogen chloride.

SCHEELE (1742-1810 A.D)

Cavendish discovered hydrogen.

LAVOISIER (1743-1794 A.D)

 Lavoisier discovered that oxygen constituted about on fifth of air.
 He discovered law of the conservation of the mass.

JOHN DALTON (1766-1844 A.D)

 John Dalton proposed atomic theory of matter.
 He also proposed that atom is the tiny indivisible & indestructible particle of element.

GAY-LUSSAC (1778-1850 A.D)

 Gay-Lussac discovered several chemical and physical properties of air and other gases.
 He discovered that water is composed of two parts hydrogen and one part oxygen by volume.

AVOGADRO (1776-1856 A.D)

Avogadro is well known for his law; he states that at a fixed temperature and pressure, equal volumes of
gases contain the same number of molecules.

JACQUES CHARLES (1746-1823 A.D)

Jacques Charles is well known for his gas law, known as Charles law.

PETIT (1791-1820 A.D)

 Petit and others led to the determination of relative atomic and molecular masses of many substances.
 He also gave an empirical law concerning the specific heat of elements.

J.J BERZULIUS (1779-1848 A.D)

J.J Berzellus introduced the idea of symbols, formulae and chemical equations to make the study more
systematic

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 MENDELEEV (1834-1907 A.D)
Mendeleav discovered the periodic arrangement of the elements and also proposed Mendeleev’s periodic
law.
ARRHENIUS (1859-1927 A.D)
 Arrhenius is renowned for his theory known as “theory of ionization”.
 He also described the nature of acids and bases.

M. FARADAY (1791-1867 A.D)

M. Faraday also discovered the laws of electrolysis and contributed to the study of electromagnetism and
electrochemistry.

J.J. THOMSON (1856-1867 A.D)

J.J. Thomson discovered the “Electrons” by his renowned experiment known as ‘Discharge Tube Experiment’.

NIELS BOHR (1885-1962 A.D)

Niel Bohr proposed a theory for the hydrogen atom based on quantum theory and thoroughly demonstrated
the structure of an atom and hydrogen spectrum.

RUTHERFORD (1871-1937 A.D)

 Rutherford discovered alpha and beta rays, and proposed the laws of radioactive decay.
 He also proposed the nuclear structure of the atom.

SCHRODINGER (1887-1961 A.D)

Schrodinger proposed quantum mechanical model of atom.

DE BROGLIE (1892-1987 A.D)

De Broglie proposed hypothesis about wave particle and dual nature of electron.

SATYENDRA NATH BOSE (1894-1974 A.D)

Satyendra Nath Bose proposed fourth state of matter (i.e. plasma).

ALBERT EINSTEIN (1879-1955 A.D)

 Albert Einstein proposed fourth state of matter (i.e. plasma).
 He also renowned for his work in the field of physics (Theory of Relativity).
ERIC CORNELL (1961 – Alive)
Eric Cornell along with Carl Weiman synthesized the 1st Bose-Einstein condensate in 1995.
(Nobel Prize winner of 2001)
CARL WEIMAN (1951- Alive)
Eric Cornell along with Carl Weiman synthesized the 1st Bose –Einstein condensate in 1995.
(Noble Prize winner of 2001)

Q.03: Define chemistry?

Ans: Chemistry is the main branch of science it deals with study about structure properties and composition
of matter, It also deals with the study about changes and principles which given on these change is called
chemistry.

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Q.04: Describe the Role of chemistry in our daily life.
Ans: Without chemistry it would be extremely hard for us to live. WE need chemistry and chemicals for
everything we do. Chemistry plays an important role in the modern world. Food, synthetic fiber, plastics medicines,
soaps and detergents, cosmetics, cement, gases, fertilizers and explosives are the major gifts of chemistry.
Examples of important role of chemistry in daily life:
Our planet earth has only life in the all planets of universe, due to existence of important chemical compound water.
The water is a basic need of humans, animals and plants. Chemistry helps us in providing our everyday needs of
food, clothing, glass, fertilizers, plastic, ceramics, synthetic fiber and polymers. Disorders in the chemical reactions
take place in humans, animals and plants which may cause different diseases can be overcome with the help of
chemistry. Chemistry helps us to control the spread of diseases for example chlorine treatment of water kills
pathogenic organisms in water which in turn provide pure water for drinking. A number of chemicals such as PCV
(polyvinyl chloride), bleaching agents have been producing from chlorine for many decades. Chemistry plays an
important role in in the protection of environment. Chemistry helps to discover new sources of energy.

Q.05: Describe the branches of chemistry.

Ans: Branches of Chemistry Due to the wide scope of chemistry in this world, it can be divided into the following
branches.
Physical chemistry is the branch of chemistry which deals with the relationship between composition and physical
properties of matter with the changes in them.
Or
It deals with the laws and the principles governing the combination of atoms and molecules in chemical reactions.

Organic chemistry is the branch of chemistry which deals with hydrocarbons and their derivatives.

Inorganic Chemistry is the branch of chemistry which deals with the study of all elements and heir (generally
obtained from non-living organisms i.e. from minerals.) except hydrocarbons.

Biochemistry It is the branch of chemistry that deals with the compounds of living organism i.e. plants and animal
and their metabolism in the living bodies and synthesis in the living bodies such as carbohydrates, proteins and fats.

Industrial Chemistry is the branch chemistry which deals with the study of chemical processes involved in the
chemical industries for the manufacture of synthetic products like fertilizers, glass, cement, and medicines etc.

Nuclear chemistry is the branch of chemistry which deals with the radioactivity, nuclear processes and properties.

Environmental Chemistry it is the branch of chemistry which deals with the study of the interactions of chemical
material and their effects on the environment of animals and plants.

Analytical chemistry is the branch of chemistry which deals with separation and analysis kind, quality and quantity
of various components in given a substance.

Medicinal chemistry is the branch of chemistry which deals with synthetic organic chemistry, pharmacology and
various biological specialties.

Quantum chemistry is the branch of chemistry which deals with applications, mechanics experiments of physical
models in chemical system. It is also called molecular quantum mechanics.

Green Chemistry is the branch of chemistry which deals with study of processes and designing products, which are
composed of less hazardous substances. It is also known as sustainable chemistry.

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Q.06: What is meant by Matter?
Ans: Anything which occupies space (volume), has mass and can be perceived by our Physical senses is called
matter.
CHARACTERISTICS OF MATTER
1. VOLUME
The matter must occupy space. The space occupied by matter is called volume.
2. MASS
It represents the quantity of matter, which can be found by physical balance.
3. WEIGHT
It represents the pull of gravity on matter. It can be found by sprig balance.
4. PERECEPTION BY PHYSICAL SENSES
It is perceived by our physical senses, i.e. sense of touch, sense of hearing, sense of sight, sense of smell and
sense of taste.
STATES OF MATTER
Matter is commonly found in four states
1. Solid 2. Liquid 3. Gas 4. Plasma
1. SOLID
A solid is a state of matter which has definite shape and definite volume.
CHARACTERISTICS
 Molecules of a solid are very closely packed and vibrate to and fro about heir mean position.
 It is compressed or squeezed appreciably by high pressure.
 Solids slightly expand on hearing.
EXAMPLES OF SOLIDS
2. LIQUID
A liquid is a state of matter which has definite volume but not definite shape.
CHARACTERISTICS
 Molecules of liquids are less closely packed then solids.
 It is not compressible to negligible extent.
 Liquids expand on hearing.
 Molecules of liquids move away from each other.
 It takes the shape of its container.
EXAPPLES OF LIQUIDS
Water, alcohol, benzene, milk, mercury, kerosene oil, etc.
3. GASES
A gas is a state of matter, which has definite mass, but neither definite shape nor definite volume.
CHARACTERISTICS
 Molecules of gases are very widely separated.
 Gas can be compressed or squeezed into smaller volume.
 Gas expend on heating.
 Molecules of gases move freely from one place to other.
 It tasks the shape of its container.
 A gas diffuses, that is, it distributes itself throughout a vessel.
EXAPPLES OF GASES
Oxygen, nitrogen, carbon dioxide, hydrogen, sulphur dioxide etc.
4. PLASMA
Plasma is the ionic state of matter in which gas is provided a sufficient energy to free electrons from atoms
and molecules and both species i.e. ions and electrons to co-exist.
It mean this state exist between solid & liquid intenses of characteristics.

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Q.07: What does atom means?
Ans: The smallest particle of an element that has the properties of element is called atom.
 Atoms are the basic units of matter and define structure of elements.
 Atoms are made up of three particles proton, neuron and electron.
 Where neutron and proton are situated in nucleus and electron are revolving around the nucleus.
EXAMPLES
1. Hydrogen H 2. Sodium Na 3. Potassium K 4. Chlorine CI
Q.08: What is meant by Molecule? Describe different types of molecules based on number of atoms.
Ans: Molecule is the smallest particle of a substance that can exist independently and has the
properties of the substance.
EXAPLANATION
Molecules are made up of atoms that are held together by chemical bonds. These bonds from as a
result of the sharing or exchange of electrons among atoms.
(OR)
The smallest unit of an element or a compound which can exist independently is called molecule.

TYPES OF MOLECULES ON THE BAISIS THE BASIS OF NUMBER OF ATOMS

There are four types of molecules on the basis of number of atoms.
 Mono atomic molecule
 Di atomic molecule
 Tri atomic molecule
 Poly atomic molecule
1. MONO-ATOMIC MOLECULE
Molecule consists of one atom is called mono atomic molecule.
EXAMPLES
Helium (He), Neon (Ne), Argon (Ar) etc.
2. DI-ATOMIC MOLECULE
Molecule consist of two atoms is called di atomic molecule.
EXAMPLES
Hydrogen (H2), Oxygen (O2), Chlorine (CI2) etc.
3. TRI – ATOMIC MOLECULE
Molecule consists of three atoms is called tri atomic molecule.
EXAMPLES
H2O, CO2, O3 etc.
4. POLY ATOMIC MOLECULE
Molecule consists of many (more than three) atoms is called poly atomic molecule.
EXAMPLES
CH4, H2SO4, C6H12O6 etc.
Q.09: What are the types of molecules on the basis of type of atoms?
Ans: There are two types of molecules on the basis of types of atoms.
 Homo atomic molecule
 Hetero atomic molecule
1. HOMO-ATOMIC MOLECULE
Molecule consist of same type of atoms is called homo atomic molecule.
EXAMPLES

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 H2, O2, P4, S8, etc.
2. HETERO-ATOMIC MOLECULE
Molecule consists of different type of atoms is called hetero atomic molecule.
EXAMPLES
H2O, CO2, H2SO4 etc.
Q.10: Define the term substance with example.
Ans: A piece of matter in pure form is known as a substance.
 Every substance has a fixed composition and specific properties.
 Every substance has its specific physical and chemical properties.
EXAMPLES OF PURE SUBSTANCES
Examples of pure substances are
 Diamond (C)
 Water (H2O)
 Table salt (NaCI)
 Sulphur (S)
 Baking soda (NaHCO3) etc.
Q.11: Define the term Element? Give characteristics of elements.
CHARACTERISTICS OF ELEMENT
 An element is made up of same type of atoms.
 Elements having atoms of same atomic number.
 Element cannot be decomposed into simple substances by ordinary chemical reactions.
 Elements occur in nature in free or combined form in solid, liquid and gases state.
 Now 118 elements have been discovered.
EXAMPLES
Carbon, oxygen, nitrogen, calcium, and gold are some examples of elements.
Q.12: Describe the classification of elements on the basis of their properties.
Ans: Elements can be classified into the following three groups on the basis of their properties.
 Metals
 Non-metals
 Metalloids
1. METALS
DEFINITION
Elements, which are good conductors of heat and electricity, malleable and ductile, and have a
metallic luster are called metals.
EXAMPLES
 Sodium
 Potassium
 Gold
 Copper
CHARACTERISTICS
 All of them has luster and are malleable (i.e. can be spread out into sheets) and are ductile (can be
drawn into wire).
 Metals are good conductors of heat and electricity,
2. NON-METALS

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 DEFINITION
Elements, which are bad conductors of heat and electricity, are neither malleable nor ductile, and
have no metallic lustre are called non-metals.
EXAMPLES
 Carbon
 Nitrogen
 Chlorine
CHARACTERISTICS
 Non-metals are bad or poor-conductors of heat and electricity.
 Non-metals are found in solid, liquid and gaseous states.
3. METALLOIDS
DEFINITION
A metalloid is an element that has properties that are intermediate between those of metals and
non-metals.
(OR)
An element (e.g. arsenic, antimony, or tin) whose properties are intermediate between those of
metals or semiconductors.
CHARACTERISTICS
 These are the elements, which exhibit dual character. That is why they show the properties of both
metals as well as non-metals.
 Most are silvery in appearance and all are solid at room temperature.
 Metalloids are brittle rather than malleable or ductile.
 They are semiconductor.
EXAPMPLES
 Arsenic (As)
 Antimony (Sb)
 Tin (Sn)
Q.13: Define compound and give some examples.
Ans: Substance which is formed by combination of two or more than two elements which are
combined chemically in a fixed proportion is called compound.
SOME COMMON COMPUONDS WITH THEIR FORMULAE
COMPOUNDS CHEMICAL FORMULAE
Water H2O
Silicon dioxide (sand) SiO2
Sodium hydroxide (caustic soda) NaOH
Sodium carbonate (washing soda) Na2CO310 H2O
Calcium carbonate (lime stone) CaCO3
Sugar C12H22O11
Ammonia NH3
Sulphuric H2SO4
Calcium oxide CaO
Q.14: Define the term Mixture and give characteristics of mixture.
Ans: Substance, which is formed by combination of two or more than two substances which are
combined physically in a variable proportion is called mixture.

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 CHARACTERISTICS
 The component substances of mixture retain their chemical properties.
 Components of the mixture can be separated by simple physical methods such as filtration
evaporation, distillation or crystallization.
EXAMPLES OF MIXTURES
1. Brass 2. Soil 3. Air
Q.15: Describe the types of mixture.
Ans: There are two types of mixtures.
1. Heterogeneous mixture
2. Homogeneous mixture
1. HETEROGENEOUS MIXTURE
DEFENITION
Those mixtures, which do not have, uniform composition throughout their mass are called
heterogeneous mixtures.
EXAMPLES
1. Rocks 2. Soil 3. Food products 4. Ice cream
2. HOMOGENEOUS MIXTURE
DEFINITON
Those mixtures, which have uniform composition throughout their mass, are called homogeneous
mixtures.
EXAMPLES
1. Salt and water 2. Sugar and water 3. Air
Q.16: Define the term symbol. Give some examples and write down the rules of writing symbols of
elements.
Ans: A symbol is an abbreviation for the chemical name of an element and represents only one
atom of the element.
RULES FOR SYMBOL WRITING
1. Usually the first letter of English name of an element (in capital) is taken as symbol.
EXAMPLES
ELEMENTS SYMBOLS ELEMENTS SYMBOLS
Boron B Carbon C
Oxygen O Sulfur S
Nitrogen N Hydrogen H
Fluorine F Iodine I
2. When two or more elements begin with the same letter, then their symbols were composed of two
letters in which first capital letter is followed by a second small letter.
EXAMPLES
ELEMENTS SYMBOLS ELEMENTS SYMBOLS
Calcium Ca Cadmium Cd
Cobalt Co Zinc Zn
Chromium Cr Zirconium Zr
Cesium Cs Barium Ba
Chlorine CI Bromine Br
Beryllium Be Magnesium Mg
Bismuth Bi Manganese Mn

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 3. Sometimes the symbol of the element is derived from the Latin name of the element.
4. EXAMPLES
ELEMENTS LATIN NAMES SYMBOLS ELEMENTS LATIN NAMES SYMBOLS
Copper Cuprum Cu Silver Argentums Ag
Gold Aurum Au Mercury Hydrargyrum Hg
Lead Plumbum Pb Iron Ferrum Fe
Tin Stannum Sn Potassium Kalium K
Sodium Natrium Na

Q.17: What do you understand by the term valency? Give some example.
Ans: The power of an element to combine with other elements is called valency.
STANDARD OF VALENCY
Valency of hydrogen, which is ‘1’, is taken as the standard of valency.
OTHER DEFINTIONS
1. The number of hydrogen atoms, which combine with or displace one atom of an element or a group of the
radical, is called valency.
EXAMPLE
 Valency of chlorine is one (1) because one atom of hydrogen combines with one atom of chlorine of from
HCI
2. The number of unpaired electrons in valence orbit of an atom is also called valency of that element.
EXAMPLE
 Valency of chlorine is one because it has one unpaired electron.
3. The number of electrons shared by an atom of the element is called valency.
EXAMPLES
 Valency of chlorine is one because it has one shared electron.
 Valency of nitrogen is three because it has three shared electrons.
4. The number of electrons lost or gained by an atom of the element is called valency.
EXAMPLE
 Valency of sodium is one because it loses on electron from its outer orbit.
Q.18: Discuss the various types of valency with example.
Ans: On the basis of loss or gain of electrons valency can be classified into the following two types.
 Positive valency
 Negative valancy
 POSITIVE VALANC
Valency of an atom is positive when it loses one or more electrons.
EXAMPLE
In sodium chloride valency of sodium is positive because it loses one electrons.
Na Na+ + e-
2. NEGATIVE VALENCY
Valency of an atom is negative when it gains one or more electrons.
EXAMPLE
In sodium chloride valency of chlorine is negative because it gains one electrons.
CI + e - CI-1
Q.19: Describe the types of atoms based on valency.
Ans: on the bases of magnitude of valency atoms can be classified into the following types.
 Monovalent
 Divalent
 Trivalent

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 1. MONOVALENT
Atom which has one unpaired electron or which gains or losses one electron is called monovalent element.
EXAMPLE
 Sodium +1
2. DIVALENT
Atom which has two unpaired electron or which gains or losses one electron is called divalent element.
EXAMPLE
 Calcium +2
3. TRIVALENT
Atom which has three unpaired electrons or which losses three electrons is called trivalent element.
 Aluminum +3
Q.20: Define the term chemical formula.
Ans: The representation of molecule of a substance in terms of symbols is called formula.
(OR)
Formula which represents the symbol of elements and ratio of elements to one another in a compound is
called chemical formula.
Q.21: Describe the types of chemical formula.
Ans: By formula we mean not only the elements present but also ratios in which the atoms are combined.
Hence we will discuss two types of formula i.e.
 Empirical formula
 Molecular formula
Q.22: Define empirical formula with example.
Ans: A chemical formula that gives only the relative number of atoms present in a molecule is called
empirical formula.
EXAMPLE
1. The molecular formula of benzene is C2H6 this formula indicates that benzene molecule consists of (6) carbon
atoms and (6) hydrogen atoms. The ratio of carbon (C) to hydrogen (H) atoms in this molecule is 6:6 or 1:1
The empirical formula of benzene is, therefore written as (CH)
2. Consider another example, the molecule of glucose (C2H12O6) in which the ratio of C, H and O atoms is 6:12:6
i.e. 1:2:1. The empirical formula of glucose is, therefore, (CH2O)
Q.23: What information is obtained from an empirical formula?
Ans: Empirical formula tells us about the type of element present in the molecule.
Empirical formula shows simplest ratio of each atoms present in a molecule.
Empirical formula does not show the actual number of atoms in the molecule.
Empirical formula cannot show the structure of compound.
Q.24: Define Molecular with example.
Ans: Formula which shows the actual number and type of atoms of each element present in a molecule is
called molecular formula.
(OR)
A shorthand notation for the molecule of a substance in terms of the symbols that shows actual number of
atoms of each element present in one molecule of that substance is called its molecular formula.
Q.25: What information is obtained from a molecular formula?
Ans: It represents name of substance.
It represents the true composition of a molecule of the compound.
It gives the actual number of atoms of all the elements present in one molecule of substance.
It may be same as empirical formula e.g. CO2.
Q.26: Define the term atomic number. Give some examples.
Ans: The number of protons in the nucleus of an atom is called the atomic number.

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 EXAMPLES
For examples, atomic number of carbon (C) is 6. This means that each carbon atom has 6 protons and 6
electrons in it. The atomic number of nitrogen (N) is 7, it means that nitrogen atom has 7 protons and 7
electrons in it.
NOTATION
Atomic number is denoted by Z. Atomic number is written as subscript on the left hand side of chemical
symbol.
EXAMPLE
6C and 7N
Q.27: Define the term atomic mass or mass number.
The sum of the number of neutrons and protons in the nucleus of an atom is called its atomic mass or mass
number.
NOTAION
Atomic mass or mass number is denoted by A.
Atomic mass written as superscript on the right hand side of chemical formula
Q.28: Define the term molecular mass.
Ans: The molecular mass is the sum of atomic masses of all the atoms present in on molecule of a
substance.
UNIT
EXAMPLES
The molecular mass of H2 =2 = 02 amu
The molecular mass of =2 16 = 32 amu
The molecular mass of =(2 1) + 16 = 18 amu
The molecular mass of = (6 12) + (16 = 78 amu
Q.29: Define the term formula mass.
Ans: In case of ionic compounds formula mass is the sum of atomic masses of all the atoms present in one
formula unit of a substance.
UNIT
Unit of formula mass is atomic mass unit (a.m.u).

CHEMMICAL SPECIES
Q.30: Define the term chemical species?
Ans: Chemical species is a chemical entity of particular atoms, ions or molecules.
EXAMPLE
If one molecule is identical to another we can say the same chemical species.
Q.31: What is meant by the term ION? Describe different types of ions with example.
Ans: An atom or group of atoms having any charge on it is called ion.
TYPES OF IONS
There are two types of ions on the basis of nature of charge.
1. Cation 2. Anion
1. CATION
Atom or group of atoms having positive charge is called cation.
FORMATION OF CATION
Cation is formed by the loss of one or more electron from the outer most shell of atom.
Na Na+ + e-
2. ANION
Atom or group of atoms having negative charge is called anion.
FORMATIO OF ANION
Anion is formed by the gain of one or more electron from the atom.

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 CI + e- CI-

Q.32: What do you understand by the term molecular ion? Describe its types with suitable examples.
Ans: When a molecule loses or gains electrons called molecular ion.
EXAMPLE
CH4+
TYPES OF MOLECUAR IONS
There are two types of molecular ions on the basis of nature of charge.
 Cationic molecular ion
 Anionic molecular ion
1. CATIONIC MILECULAR ION
Molecule (group of atoms) having positive charge is called cationic molecular ion.
2. ANIONIC MOLECULAR ION
Molecule (group of atoms) having negative charge is called anionic molecular ion.
FORMATION OF CATIONIC MOLECULAR ION
Anionic molecular ion is formed by the gain of one or more electron.
Q.33: Define the term free radical. Give some examples.
Ans: Free radicals are atoms and group of atoms having number of unpaired electrons.
REPRESENTATION
It is represented by putting a dot over the symbol of an element.
EXAMPLES
Ho, CIo, oCH3
FORMATIO OF FREE RADICALS
Free radicals are formed when hemolytic breakage of bond between tow atoms takes place by the
absorption of heat or light energy.
Q.34: Define Chemical equation. Describe all important terms related to chemical equations.
Ans: Chemical equation is short hand method of describing (expression) the chemical reaction, in terms of
symbols and formulae of the substances involved in a chemical reaction.
(OR)
FEW IMPORTANT TERMS
Let us try to know a few terms used in writing a chemical reaction are called reactants. The reactants are
always written on the left hand side in a chemical equation (of irreversible reaction).
1. REACTIANTS
The substance/substances which take part in a chemical reaction are called reactants. The reactants are
always written on the left hand side in a chemical equation (of irreversible reaction).
2. PRODUCTS
Substance/substances formed as a result of chemical change during a chemical reaction are called products.
The products are always written on the right hand side in a chemical equation (of irreversible reaction).
3. CO-EFFEICIENTS
The numbers, in front of formulae in a chemical equation are called coefficients (they show the number of
molecules that react with each other).
4. ARROW
The recants and products are separated from one another by using single arrow ( or double arrow
( ) depending upon type of reaction.
5. EXPRESSON
The expressions (s), (g), and (I) shows the states, solid, gaseous and liquid reactants products whereas (aq)
express that substance is in the form of solution.

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Q.35: Describe the structure of chemical equation with suitable example.
Ans: A chemical equation consists of formulae or symbols of reactants connected by plus sign (+) and an
arrow ( followed by the formulae or symbols of products, connected by plus sign (+). The sign of an arrow
( is read “to yield” or “to form”. It also shows the direction in which reaction is predominant.
EXAMPLE
For illustration, when two molecules of hydrogen (H2) combine (react) with one molecule of oxygen (O2) to
give two molecules of water (H2O), instead of writing the full names substances; chemist represents this
chemical reaction in the form of the following equation e.g.
BALANCE EQUATION
Q.36: What is meant by balance chemical equation?
Ans: A chemical equation in which number of atoms of each element is same on the side of reactants and
products in called balance equation.
EXAMPLES
Zn + 2HCI ZnCI2 + H2
2Na + CI2 2NaCI
Q.37: What is meant by unbalance chemical equation?
UNBALANCED EQUATION
Ans: A chemical equation, in which number of atoms of various elements towards the side of reactants is not
equal to number of atoms various elements towards the side of products, is called unbalanced equation.
EXAMPLES
Zn + HCI ZnCI2 + H2
Na + CI2 NaCI
RULES FOR BALANCING A CHEMICAL EQUATION
Q.38: Write down the rules for balancing chemical equations.
Ans: 1. Write the correct formulae of all reactants on the left side and the formulae of products on the right
side of an equation.
2. Balance the number of atoms on each side.
3. If he number of atoms may appear more on one side than the other, balance the equation by inspection
method for this, multiply the formula by coefficient so as make the number of atoms, same on both sides of
an equation.
4. The covalent molecules of hydrogen, oxygen, nitrogen and chlorine exist as diatomic molecules e.g. H2, O2,
N2, and CI2, rather than isolated atoms, hence we must write them as such in chemical equation.
5. Finally, check the balanced equation, to be sure that the number and kind of atoms are the same on both
sides of equation.
Q.39: Define the term gram atomic mass with example.
Ans: The atomic mass of an element expressed in grams is called gram atomic mass.
EXAMPLES
 The gram atomic mass of hydrogen (H) = 1g
 The gram atomic mass of Helium (He) = 4g
Q.40: Define the term gram molecular mass with example.
Ans: Molecular mass of any element or compound expressed in grams is called gram molecular mass.
EXAMPLES
 Gram molecular mass of hydrogen molecule (H2) = 2g
 Gram molecular mass of chlorine molecule (CI2) = 71g
Q.41: Define the term gram formula mass with example.
Ans: The formula mass of an ionic compound expressed in grams is called gram formula mass.
EXAMPLES
 Gram formula mass of NaCI = 58.5g

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  Gram formula mass of CaCO3 = 100g
Q.42: Define the term Mole with example.
Ans: The atomic mass, molecular mass formula mass of a substance expressed in grams is called mole.
(OR)
A mole represents the quantity of material which contains one Avogadro’s number (6.02 1023) of chemical
units.
EXAMPLES
Since atomic mass of carbon is 12 therefore 12 gram of carbon = I mole of carbon
Since atomic mass copper is 63.5 therefore 63.5 gram of Cu = I mole of copper
FORMULA
Number of moles =

Number of moles =
OR
Mass of substance in gram = Number of mole Molar mass
Q.43: Define the term Avogadro’s number with example.
Ans: Avogadro an Italian scientist calculated the number of atoms, molecules or ions present in one mole.
The value is found to be 6.02 1023. This value is represented by NA and is called as Avogadro’s number.
OR
1. Mole of any substance always contains 6.02 1023. Particles (atoms, ions, molecules or formula units)
irrespective to the state of substance. This constant number is called Avogadro’s number.
Q.44: What are Chemical Calculations?
Ans: In all types of chemical calculations we calculate number of moles and number of particles of a
substance. These calculations are based on mole. In the sequence of calculation first moles calculated then
number of particles.
Q.45: Describe the relationship between mole and mass of any substance.
Ans: In this calculation we calculate number of moles of a substance with the help of the following equation.
Number of moles =
OR
Mass of substance = number of miles x molar mass
EXAMPLE 1
A cion of silver (Ag) having 8.5 gm weight. Calculate the number of moles of silver in coin?
DATA
Given mass of Ag = 8.5 g
Molar mass of Ag = 108 g
Number of moles = ?
SOLUTION
Number of mole =

Number of mole =
Number of moles = 0.0787 mol

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 MOLE-PARTICLE CALCULATIONS
Q.46: Describe the relationship between mole and number of particles of any substance.
Ans: In this calculation we calculate number of moles a substance in the given number of Particles
(atom, molecules or formula unit).
Number of moles =

= 23

We can calculate the number of particles as:

Number of particles = number of moles x 6.02 x1023
EXAMPLE 1
Calculate the number of moles, number of molecules of atoms present in 10gm of H2SO4?
DATA
Number of moles =?
Number of molecules = ?
Number of atoms =?
Mass of H2SO4 = 10 g
Molar mass of H2SO4 = 1 2 + 32 + 16 4 = 98 g

SOLUTION
Number of moles =

Number of moles =
Number of moles = 0.1020

CALUCLATION
Number of molecules= number of moles x 6.02 x 1023
Number of molecules = number of moles x 6.02 x 1023
= 0.1020x 6.02 x 1023
= 0.61428 x 1023
= 6.1428 x 1022
Since, each molecule of H2SO4 contains 7 atoms.
Therefore, number of atoms in 6.1428 1022 molecules of H2SO4 = 7 6.1428 1022 atoms
= 4.3 1023 atoms
Q.47: Describe the relationship between mole and volume of any substance.
Ans: According to Avogadro “one gram mole of any gas at Standard temperature and pressure (STP) always
occupies a volume of 22.4 dm3, this constant volume is known as Molar volume,”
Where,
Standard temperature is 0 oC or 273K
Standard pressure is 1 atm or 760 torr.
I dm3 = 1 L
EXAMPLE 1
How many liters of carbon dioxide would be produced if 0. 450 mole of carbon monoxide reacts with excess
oxygen at STP?

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SOLUTION
The equation for the reaction is
2CO + O2 2CO2

2 moles 2 22.4 L (44.8L)

From above equation:

2. Moles of CO produces = 44.8 litre of CO2

1. Mole of Co produces = litre of CO2

0.45 mole of CO produces = 0.45 litre of CO2

0.45 moles of CO produces = 10.08 litre of CO2

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