Section B Chapter 1 covalent bond

Covalent bond:
the bond which is formed by mutual sharing of electron is called covalent bond.

this bond made by only non-metal by sharing.

Ionic bond :
the bond which is formed by permanent displacement of electron is called ionic bond.

this bond made by only metal and non-metal.

Factors favouring covalent bond:
1.high ionisation .
2.high electro affinity and high electronegativity.
3.high nuclear charge.
4.valence shell having 5,6,7 electron.

characteristic of covalent compound:

1.melting point and boiling low:
covalent compound have low melting point and boiling point because little energy is required to break weak intermolecular force.

2.Solubility: covalent compounds are generally soluble in organic solvent like benzene.

3.physical state: covalent compound can exist as gas due to the presence of weak forces. however they exist as soft solid only when their molecules weight are high.

4.directional characteristics of covalent compound: covalent compound is formed by overlapping of atomic orbital. more is the extent of overlapping stronger is the bond since orbital are directed in space. so covalent bond have direction nature. hence covalent compound acquire a particle shape or geometry.
the shape and geometry can be explain on the basis of VSEPR theory.

VSEPR THEORY:

1.A covalent molecule always have certain number of electron in the valence shell of Central atom.

2. the valence electron of Central atom may either form covalent bond with electron if surrounding atom or may exist as lone pair.
the bond pair try to stay as far apart as possible to acquire a state of minimum energy or maximum stability. these bond pair or lone pair tends to repel one another. the order of repulsion is.

Lone pair -Lone pair> Lone pair-
Bond pair>bond pair-bond pair.

3.hyberdisation: the phenomenon of intermixing of various orbital which differ slightly in energy to give rise to new orbital of indentical energy is called hyberdisation.

hybrid orbital form stronger covalent bond became they are more directional.

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