ATOMIC NUMBER

• The total number of protons, present in the nucleus of an atom, is known as atomic number. The number of protons of an atom determines the atomic number. Atomic number is denoted by ‘Z’. Protons and neutrons collectively are known as nucleons.

Mass Number

• The sum of the total number of protons and neutrons, present in the nucleus of an atom, is known as mass number.

ISOBARS

• Atoms of different elements with different atomic numbers, which have the same mass number, are known as Isobars. E.g., calcium’s atomic number is 20and argon’s atomic number is 18; further, the number of electrons in these atoms is different, but the mass number of both these elements is 40.

CHEMICAL REACTIONS & EQUATIONS

Introduction

• A process in which one or more chemical substances react with other chemical substance and converted to one or more different substances is known as chemical reaction.

CHEMICAL EQUATION

• A chemical equation is the symbolic demonstration of a chemical reaction; it is represented through symbols and formulae.

E.g.

Magnesium + Oxygen = Magnesium Oxide

Mg + O₂ = MgO

• The substances magnesium and oxygen are known as reactants and the result of reaction, i.e., magnesium oxide is known as product.

• Remember, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.

• The number of atoms of each element always remains same, before and after the chemical reaction.

TYPES OF CHEMICAL REACTION

• Following are the major types of chemical reaction −
  • Combination Reaction
  • Decomposition Reaction
  • Displacement Reaction
• Let’s discuss each of them in brief −

COMBINATION REACTION

• When two or more substances (i.e., elements or compounds) react to form a single product, such reaction is known as combination reaction.

E.g.

CaO(s) +H₂O (1) →Ca (OH)₂(aq)

(Quick lime) (Slaked lime)

• As illustrated in the above reaction, calcium oxide and water reacted (or combined) to form a single product, known as calcium hydroxide.
• The chemical reaction in which heat is also released along with the formation of product is known as exothermic chemical reactions.

DECOMPOSITION REACTION

• The reaction, in which a single reactant breaks down into simpler products, is known as a decomposition reaction.

E.g.

• In the above given reaction, Ferrous Sulphate Crystals (i.e., FeSO₄, 7H₂O), when heated, it loses water and the color of the crystal’s changes. Finally, it decomposes into ferric oxide (Fe₂O₃), Sulphur dioxide (SO₂) and Sulphur trioxide (SO₃).

DISPLACEMENT REACTION

• The reaction, in which an element displaces or removes another element, is known as displacement reaction.

E.g.

Fe(s) + CuSO4(aq)→FeSO4(aq)+Cu(s)

(Copper sulphate) + (Iron sulphate)

• In the above given reaction, iron displaced copper from copper sulphate solution and forms Iron sulphate.

OXIDATION AND REDUCTION

• If a substance gains oxygen during a reaction, it is known as oxidation. On the other hand, in a reaction, if a substance loses oxygen, it is known as reduction. E.g.

• In the above given reaction, the copper oxide loses oxygen and hence reduced (i.e. reduction); on the other hand, hydrogen gains oxygen and hence oxidized (i.e. oxidation).

CORROSION

• When a metal is attacked by substances found in the immediate environment, such as moisture, acids, etc., it is known as corrosion. E.g., the black coating on silver, the green coating on copper, etc.,

RANCIDITY

When fats and oils are getting oxidized, the process is known as rancidity. Their smell, taste, color, etc. also change; likewise, it made food unsafe for consumption.