Electronic configuration of carbon atom : C : σ1s²2s²p².
In the excited state, the orbital picture of carbon can be represented as:

Hence, carbon atom undergoes sp³ hybridisation in CH⁴ molecule and takes tetrahedral shape.

For a square planar shape, the hybridisation of the central atom has to be dsp³, However, an atom of carbon does not have d-orbitals to undergo dsp3 hybridisation. Hence, the structure of CH₄ is tetrahedral.

₁₂Mg = 2,8, 2\(\therefore Lewis\ symbol=\overset { . }{ Mg. } \)
₁₁Na = 2,8, 1\(\therefore Lewis\ symbol=\overset { . }{ Na } \)
₅B = 2, 3 \(\therefore Lewis\ symbol=.\overset { . }{ B } .\)
₈O = 2,6 \(\therefore Lewis\ symbol=:\overset { .. }{ B } :\)
₇N = 2,5 \(\therefore Lewis\ symbol=:\overset { .. }{ N } :\)
₃sBr = 2,8,18,7 \(\therefore Lewis\ symbol=:\overset { .. }{ Br } .\)

(i) The extent of ionic character in a covalent bond can be related to the electronegativity difference of the bonded atoms.
(ii) In a typical polar molecule A^ઠ- - B^ઠ++, the electronegativity difference (X_A - X_B) can be used to predict the percentage of the ionic character as follows:
(iii) If the electronegativity difference X_A - X_B is equal to 1.7, then the bond A - B has 50% ionic character.
(iv) If it is greater than 1.7, then the bond A - B has more than 50% ionic character.
(v) If it is lesser than 1.7, then the bond A - B has less than 50% ionic character.

(i) In the case of polyatomic molecules with two or more same bond types, the arithmetic mean of the bond energy value of the same type of bonds is considered as average bond enthalpy.
(ii) For e.g., in water, there are two OH bonds present and the energy needed to break them are not same
(iii) \({ H }_{ 2 }O_{ (g) }\longrightarrow H\left( g \right) +OH\left( g \right) \Delta { H }_{ 1 }=502kJ{ mol }^{ -1 }\)
\(OH(g)\longrightarrow H(g)+O(g)\Delta H=427KJmol\)
The average bond enthalpy of OH bond in water
=\(\cfrac { 502+427 }{ 2 } =464.5KJmol^{ -1 }\)

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

\(C^+_2\) is paramagnetic.

(i) Though the central oxygen atom in both the molecules is sp³ hybridised with two lone pairs, : dimethyl ether has greater bond angle than water molecule. 
(ii) The repulsive interaction between the two  bulky methyl groups in diethyl ether increases its bond angle.
(iii) Since no such bulky groups are present in water molecule, it does not show such repulsive interaction and hence its bond angle is shorter than dimethyl ether.

Due to the presence one lone p'air of elctrons on 'p' of PH₃ the bond angle is less than 109^o28' which is for a tetrahedron. The lone pair occupies more space.

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