Study Portal 1 – Chapter 1

Introduction of


Q.1.     Define science and chemistry.

Ans.    Science is the classified knowledge of facts gained through observation, generalization correlation and experiments. While the chemistry is the branch of science which deals with the composition, structure, properties, change and laws of matter.

Q2.      How chemistry served mankind in daily life?

Ans.    The contributions of chemistry for the welfare of human being and for the advancement of society are manifold.

Some important discoveries of chemistry for human life are as under:

  • We use many important chemicals daily such as drugs, detergents, paper, paints, pigments, insecticides, pesticides and many petrochemical products.
  • Many household items such as plastics, rubber synthetic fibres, soaps, deodorants, body and hair spray are all products of chemistry.
  • Chemistry helps us to explore and conserve natural resources.
  • Insects killing products, agriculture fertilizer productions, lather and its related products are also manufactured by using the knowledge of chemistry.

From the above information, it is clear that chemistry as a science is very much useful for human being today and in future.

Q3.   Role of chemistry as a solution to problems faced by a human being?

Ans.    The problems being faced by human being should be solved by chemistry are as under:

  • Food problem solved by the invention of fertilizers
  • Environmental protection solved by the invention of insects and bacterial killing drugs.
  • Biochemical process fermentation process plays an important role in biochemistry.
  • Radioactive elements which emit high energy rays. These rays may be used in purposeful work.


Q3.      What are the main branches of chemistry?

Ans.    Study of chemistry is divided into the following main branches.

Physical Chemistry:- Physical chemistry is defined as the branch of chemistry that deals with the relationship between the composition and physical properties of matter along with the changes in them.

Organic Chemistry:- Organic Chemistry is the study of covalent compounds of carbon and hydrogen-hydrocarbons and their derivatives.

Inorganic Chemistry:- The branch of chemistry deals with the study of all elements and their compounds except those of compounds of carbon and hydrogen-hydrocarbons and their derivatives.

Biochemistry:- It is the branch of chemistry in which we study the structure, composition and chemical reactions of substances founding living organism.

Industrial Chemistry:- The branch of chemistry that deals with the manufacturing of chemical compounds on a commercial scale are called industrial chemistry.

Nuclear Chemistry:- Nuclear chemistry is the branch of chemistry that deals with the radioactivity nuclear process and properties.

Environmental Chemistry:- It is the branch of chemistry in which we study components of the environment and the effects of human activities on the environment.

Analytical Chemistry: – Analytical Chemistry is the branch of chemistry that deals with separation and analysis of a sample to identify its components.


Q4.      Define basic definitions with examples.

Ans.    Matter, substance, Elements, compounds, mixtures, atoms, the building blocks of matter, relative atomic mass and the atomic mass unit, empirical formula, molecular formula, molecular mass and formula mass.

Matter: – Anything that has mass and occupies space is called matter e.g. water, wood, air etc. The following figure shows a simple classification of the matter.

Substance:-   It is a matter which has a particular set of characteristics which differ from the character of any other kind of matter.e.g. Oxygen, urea, glucose and salt.

Element:-      Elements can be defined as the simplest form of matter which can not be broken down into simpler form by chemical means e.g. H2, Fe, Cu, O2 and C. elements are divided into metals, non-metals and metalloid on the basis of their properties.

Compounds:-           A compound is a pure substance that is made up of two or more elements held together in fixed by natural forces called chemical bonds. The properties of compounds are different from which they are formed e.g. water, carbon dioxide, copper sulphate etc.

Mixture:-      An impure substance that contains two or more pure substance which retains their individual chemical characteristics is called a mixture e.g. air is a mixture of N2, O2 and CO2 etc. there are two types of mixture Homogenous and Heterogeneous.

Atoms:- The atom is composed of the central and outer shell of electrons.

Atomic Number: – The number of protons in the nucleus of an atom is known as its atomic number, it is represented by symbol “Z” all atoms of an element have the same number of protons in their nucleus.

Mass Number:- The total number of protons and neutrons in an atom is known as its mass number. It is represented by symbol “A”.

Relative Atomic Mass:- The light isotope of carbon (C-12) has been chosen as a standard with reference to which atomic masses of all other elements can be determined. Thus “The mass of an atom of an element relative to the mass of an atom of C-12 is called relative atomic mass.

Atomic Mass (Unit Mass):- One atomic mass unit is one-twelfth the mass of one atom of carbon-12.

Mass of one C-12 atom           = 12 a.m.u

1amu   = (mass of one C-12 atom) / 12.

Chemical Formula:- A chemical formula is a shorthand notation of a compound.

Empirical Formula:- The simplest formula of a substance which gives the relative number of atoms of each element present in the molecule of that substance is called as the empirical formula. For example:

The molecular formula of hydrogen peroxide       = H2O2

The empirical formula of hydrogen peroxide        = HO

Molecular Formula: – It gives the actual whole number ratio of atoms of each element present in a molecule of that compound. E.g. the actual ratio between C, H and O atoms in a glucose molecule is 6:12:6 so its molecular formula is C6H12O6.

Molecular Mass: – It is the sum of atomic masses of all atoms present in the molecule e.g. the molecular mass of water (H2O)

= 2 (atomic mass of H) + atomic mass of oxygen.

= 2 (1) + 16

= 18 a.m.u.

Formula Mass: – The term formula mass is used for ionic substances. Ionic compounds consist of oppositely charged ions rather than separate molecules. So we represent in an ionic compound by its formula unit and the sum of the atomic masses of all the atoms in the formula unit of a substance is called formula mass.e.g.

The formula mass of NaCl = 1´ atomic mass of Na+1´atomic mass of Cl.

= 1 ´ 23 + 1 ´ 3.5

= 58.5 a.m.u.

Chemical Species

The chemical species are the building blocks of chemical compounds. These species are atoms, ions, free radical and molecules ions.

Atom:- atom is the smallest particle of an element that cannot exist in Free State it is electrically neutral.

Ions: – Ion is an atom or group of atoms having a charge on it. There are two types of ions. (i). Cations      (ii). Anions.

  • Cations: – An atom or group of atoms having a positive charge on it is called cations. Metal atoms generally lose one or more electrons and form cations.
  • Anions: – An atom or group of atoms having a negative charge on it is called anion. Non-metals usually gain one or more electron and form anions.

Molecular Ions:- When a molecule loses or gains electrons, the resulting species is called a molecular ion. These ions are short-lived species and only exist at high-temperature molecular ions do not form ionic compounds.

Free Radical:- Free radicals are atoms or group of atoms having an odd number of the unpaired electron. Free radicals are electrically neutral species, some substance like halogens when exposed to sunlight their molecules split up into free radical.

Molecule: – Molecules are the smallest particle of a covalent compound or an element which can exist independently.

Types of Molecules:

Molecules can be classified as

  • Monoatomic: – These types of molecules contain a single atom of the same element inert gas elements are Monoatomic molecules.
  • Diatomic: – When a molecule consists of two atoms it is called diatomic molecules, for example, H2, O2, HCl, CO etc.
  • Polyatomic:- These are the molecules that are composed of more than two atoms like C6H12O6, HNO3, CuSO4 in addition to this the molecules may also be classified as homo atomic (Homo-Similar) e.g. O3, S8 and heteroatomic (hetro- different) e.g. NH3, HNO3 etc.

Avogadro’s Number and Mole

Avogadro’s Number:- The number of atoms, ions or molecules present in one mole of a substance is called Avogadro’s number. It is denoted by NA and is equal to 6.02 ´ 1023.

Mole:- The atomic mass, molecular mass or formula mass expressed in grams is called mole. 1 mole of any substance             = 6.02 x 1023.

Molar Mass:- The mass of one mole of a substance is called its molar mass.

Gram Atomic Mass:- Atomic mass of an element expressed in grams is called gram atomic mass.

Gram Molecular Mass:- Molecular mass of an element or a compound expressed in grams is called gram molecular mass.

Gram Formula Mass:- Formula mass of an ionic compound expressed in grams is called gram formula mass.

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