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Monday, 30 March 2020

Facts about Chemical Reactions

Facts about Chemical Bonding


The force that holds together the different atoms in a molecule is called Chemical Bonding.

Types of Bonding

The bond formed by the transfer of electrons from one atom to another is called ionic bond or electrovalent bond.

Ionic bond was proposed by Kossel.

In covalent bonds the atoms are linked together by the sharing of electrons between the atoms.

The number of electrons contributed by an atom for sharing is known as its covalency.

van der Waals bonds act between molecules which are brought close together. They are the weakest bonds.

The attractive force which binds the hydrogen atom of one molecule with the electronegative atom of another molecule is called hydrogen bond.

In co-ordinate bond (dative bond) the elec-trons are shared and the shared pair of electrons are derived from only one atom.

Co-ordinate bond was proposed by Sidgwick.

The attractive force between mobile electrons and the metallic kernels is referred to as metallic bonds. 

Bond Characteristics

Bond length: The average distance between the centres of nuclei of two bonded atoms.

Bond energy or Bond strength: The amount of energy required to break one mole of the bond and separate the bonded atoms in the gaseous state.

Bond angles: The average angle between the bonded orbitals is known as bond angle.

Bond order: It is the number of bonds between two atoms.

Types of Bonds

1. Ionic or Covalent - Formed by transfer of electrons
2. Co-ordinate - Mutual sharing of electrons
3. Electrovalent - One-sided sharing of electrons


Facts about Types of Reactions

Chemical reaction is a process by which one or more substances get transformed into new substances.

The substance which gets transformed or which undergo chemical reaction is called reactants.

The new substance formed as a result of chemical reaction is called products.

A chemical reaction in which reactant react to produce product and the product in turn react with one another to produce the reactant is called reversible reaction.

Difference between exothermic and endothermic reaction ?

Ans: A reaction in which heat is evolved is called the exothermic reaction. A reaction in which heat is absorbed is called endothermic reaction.

The chemical reaction in which reactant react to produce product and the products does not reversibly produce reactant are called irreversible reaction.

Chemical reaction in which light energy is either absorbed or released is called photochemical reaction.

Chemical reaction in which electric energy is either absorbed or released is called electro-chemical reaction.

Combination reaction: In this type of reaction an element or compound combines with another element or compound to form a new compound.

eg: Mercury combines with oxygen to form mercuric oxide.

Decomposition reaction: In this type of re-action a compound breaks down into simpler substances.

eg: Water can be broken down by electricity to form hydrogen and oxygen.

Simple displacement or Substitution reaction: In this type of reaction one element or radical replaces another element or radical in a compound.

eg: Zinc can replace the hydrogen in hydrochloric acid to form zinc chloride and hydrogen gas.

Double displacement reaction: In this type of reaction an element or radical of one compound changes place with an element or radical of another compound.

eg: Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.

Isomerisation reaction: In this type of reaction rearrangement of atoms in a given substance takes place and new substance is formed.

eg: On heating ammonium cyanate (NH4 CNO) changes to Urea (H2NCO NH2)

Redox Reactions

Oxidation involves the addition of oxygen or the removal of hydrogen.

Oxidation involves the loss of one or more electrons.

Reduction involves the removal of oxygen or the addition of hydrogen.

Reduction, involves the gain of one or more electrons.

Oxidising agent (oxidant): Any substance which is capable of oxidising other substances and is capable of accepting or gaining electrons lost during oxidation is called oxidising agent.

Reducing agent (Reductant): Any substance which is capable of reducing other substances and is capable of releasing or losing electrons gained during reduction is called reducing agent.

The reaction in which oxidation and reduction takes place simultaneously are called redox reaction.

Oxidation number of an element indicates the number of electrons lost, gained or shared as a result of chemical bonding.

In oxidation, oxidation number increases.

In reduction, oxidation number decreases.

Oxidation number of an atom in free state is zero.

Oxidation number of alkali metals in molecule is always +1

Oxidation number of alkaline earth metals in a molecule is always +2

Sum of oxidation number of atoms in a molecule is equal to zero.

Oxidation -> Addition of oxygen -> Removal of hydrogen -> Removal of electron

Reduction -> Removal of oxygen -> Addition of hydrogen -> Addition of electron

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