\(O^{2-},N_2,C^+_2\)

\(C^+_2\) is paramagnetic.

(i) In covalent bonds, the shared pair of electrons are localized between two atoms and also covalent bonds are formed by overlap of half covalent bonds are formed by the overlap of atomic orbitals. Since atomic orbitals are directional in nature, covalent bonds are also directional. In ionic bonds, only a network of cations are anions are tightly held together by electrostatic forces. The electrostatic field of an ion is nondirectional, hence ionic compounds are also non-directional.
(ii) Oxygen atom is H₂O is sp³ hybridised with two lone pairs. Due to greater repulsive force between lone-pair-lone-pair, the bond angle is reduced from 109.5⁰ to 104.5⁰ and hence H₂O molecule acquires a bent structure.

In CO₂ molecule, carbon atom is sp-hybridised. There is no free electron in CO₂ molecule. The two sp hybrid orbitals are oriented in opposite direction forming an angle of 180⁰ .Hence H₂0 has a bent structure and CO₂ has \(O\overset { \pi }{ \underset { O- }{ = } } C\overset { \pi }{ \underset { O- }{ = } } O\) linear structure. 
(iii) Ethyne molecule is linear because both the f carbon atoms in it are sp hybridized having two unhybridised orbitals (2px and 2py). The two sp hybrid orbitals of both the carbon atoms are oriented in opposite direction forming an angleof 180⁰.

(i) The B-in BF₃ undergoes sp² hybridisation and has a triangular planar geometry. The N-in NH3 undergoes sp³ hybridisation and has pyramidal shape with one lone pair on N-atom.
(ii) Both S in SiF₄ and CI in ClO; undergo sp³ hybridisation.
(iii) Since the electronegativity of s is less than 0, H₂S possess a lower bond angle then H₂0.

In certain bond formation, one of the combining atoms donates a pair of electrons (i.e.) two electrons which are necessary for the covalent bond formation, and these electrons are shared by both the combining atoms.
These type of bonds are called co-ordinate covalent bond or co-ordinate bond. The combining atom which donates the pair of electron is called a donor atom and the other atom an acceptor atom. This bond is denoted by an arrow starting from the donor atom pointing towards the acceptor atom.

The type of mutual sharing of one or more pairs of electrons between two combining atoms results in the formation of a chemical bond called a covalent bond. If two atoms share just one pair of electron a single covalent bond is formed as in the case of hydrogen molecule. If two or three electron pairs are shared between the two combining atoms, then the covalent bond is called a double bond or a triple bond, respectively

C₂H₂, BF₃, CCl₄

'The bond angle of HSH is 92.2° and that of H₂0 is 104.5°
The higher bond angle in water molecule is due to the higher electronegativity of oxygen (in H₂0) than sulphur (in H₂S).

N₂O

Lewis Structure of Nitrogen atom
Similarly, Lewis dot structure of carbon, oxygen can be drawn as shown below.

Lewis Structures of C & O atoms
Only exception to this is helium which has only two electrons in its valence shell which is represented as a pair of dots (duet).
\(\overset{..}He\)
Lewis Structures of He atoms

Examples : SF₆, XeF₄
Shapes :
SF₆ - Octahedral
XeF₄ - Square planar

(i) Two hydrogen atoms Ha and Hb are separated by infinite distance. At this stage, there is no interaction between these two atoms and the potential energy of this system is arbitrarly taken as zero.
(ii) As these two atoms approach each other, in addition to electrostatic attractive forces between the nucleus and its own electrons, the following new forces begins to operate.

(iii) The new attractive forces (. arrows) arise between:
(a) nucleus of H_a,and valence electron of H_b (b) nucleus of H_b and the valence electron of Ha.
(iv) The new repulsive forces (arrows) arise between:
(a) the nucleus of H_a and H_b
(b) the valence electrons of H_a and H_b.
(v) The attractive forces tend to bring H_a and H_b together whereas the repulsive forces tends to push them apart.
(vi) At the initial stage, as the two hydrogen atoms approach each other, the attractive forces are stronger than repulsive forces and the potential energy decreases.
(vii) A stage is reached where the net attractive forces are exactly balanced by repulsive forces and the potential energy of the system acquires a minimum energy.
(viii) At this stage, there is a maximum overlap between the atomic orbitals of H_a, and H_b and atoms H_a and H_b are now said to be bonded together by a covalent bond.

(i) Kossel and Lewis approach to chemical bonding is based on the inertness of the noble gases which have little or no tendency to combine with other atoms.
(ii) They proposed that noble gases are stable due to their completely filled outer electronic configuration.
(iii) Elements other than noble gases try to attain the completely filled outer electronic configuration by losing, gaining or sharing one or more electrons from their outer shell.
(iv) For e.g., sodium loses one electron to form Na+ ion and chlorine accepts that electron to give chloride ion, ClrThese two ions are held together by electrostatic attractive forces, a bond known as an electrovalent bond.
\(\underset { \left[ Ne \right] { 3s }^{ ' } }{ Na } \longrightarrow { \underset { [Ne] }{ Na } }^{ + }+{ e }^{ - }\)
\(\underset { [Ne]3{ s }^{ 2 }{ 3p }^{ 2 } }{ Cl } +{ e }^{ - }\longrightarrow { \underset { [Ar] }{ Cl } }^{ - }\)
\({ Na }^{ + }+{ Cl }^{ - }\longrightarrow Nacl\)
(v) In diatomic molecules such as nitrogen and oxygen, they achieve the stable noble gas electronic configuration by mutual sharing of electrons.
(vi) Lewis introduced a scheme to represent the chemical bond and the electrons present in the outer shell of the atom called Lewis dot structure.
(vii) For example, the electronic configuration of nitrogen is 1s²2s²2p³. It has 5 electrons in its outer shell. The lewis structure of nitrogen is \(\cdot \overset { \cdot }{ N\cdot } \)
(viii) In N₂ molecule, equal sharing of 3 electrons from each nitrogen atom takes place as follows:or N≡N

Consider a situation wherein two hydrogen atoms (H_a and H_b) are separated by infinite distance. At this stage there is no interaction between these two atoms and the potential energy of this system is arbitrarily taken as zero. As these two atoms approach each other, in addition to the electrostatic attractive force between the nucleus and its own electron (purple arrows), the following new forces begins to operate. The new attractive forces (green arrows) arise between
(i) Nucleus of H_a and valence electron of H_b
(ii) Nucleus of H_b and the valence electron of H_a.
The new repulsive forces (red arrows) arise between
(i) The nucleus of H_a and H_b
(ii) Valence electrons of H_a and H_b.
The attractive forces tend to bring H_a and H_b together whereas the repulsive forces tends to push them apart. At the initial stage, as the two hydrogen atoms approach each other, the attractive forces are stronger than the repulsive forces and the potential energy decreases.
A stage is reached where the net attractive forces are exactly balanced by repulsive forces and the potential energy of the system acquires a minimum energy. At this stage, there is a maximum overlap between the atomic orbitals of H_a and H_b and the atoms H_a and H_b are now said to be bonded together by a covalent bond. The internuclear distance at this stage gives the H-H bond length and is equal to 74 pm. The liberated energy is 436 kJ mol^-1 and is known as bond energy. Since the energy is released during the bond formation, the resultant molecule is more stable. If the distance between the two atoms is decreased further, the repulsive  forces dominate the attractive forces and the potential energy of the system sharply increases.