Chemical Bonding

Definition of ionic bond

The electrostatic attraction between oppositely charged ions as a result of the complete transfer of one or more electrons

Typically formed between metals and non-metals

Definition of covalent bond

Formed when two atoms come together so that two electrons are shared between the two atoms

Between non-metals only

Definition of electronegativity

The power of a particular atom that is covalently bonded to another atom to attract the bonding pair of electrons towards itself

Scale: F > O > N where F is the most electronegative

Factors influencing electronegativity

1) Nuclear charge, where atoms in the same period with a greater nuclear charge are more likely to attract the bonding pair of e-

2) Atomic radius, which the outer electrons further from the nucleus are less likely to attract the bonding pair of e-

3) Shielding, the greater the number the lower the effective nuclear charge

High difference in electronegativity is ionic, low is covalent

How is sigma bond formed ?

When orbitals overlap end-on in a covalent bond.

The electron density is concentrated and is responsible for holding the atoms together against the mutual repulsion of the nuclei.

How is a pi bond formed?

A pi bond is formed when orbitals overlap sideways in a covalent bond

In covalent molecules;

1) Single bonds are sigma bonds

2) Double bonds consist of one sigma bond + one pi bond

3) Triple bonds consist of one sigma bond + two pi bonds

How do dative bonds form?

1) One atom has a lone pair of electrons in the outer shell

2) The other atom has an empty orbital in the outer shell

Highest electron pair repulsion to least is…

Lone-pair lone-pair >

Lone-pair bond-pair >

Bond-pair bond-pair >

Bond pair shapes and angles

Linear: 180

Trigonal planar, v-shape (one lone pair): 120

Trigonal pyramidal: 107 eg. NH3

Tetrahedral: 109.5 eg. CH4

V-shape (two lone pair): 104.5 eg. H2O

Octahedral: 90

Alkane, Alkene, Alkyne

Alkane: sp3, where one 2s orbital uses three 2p orbitals

Alkene: sp2, where one 2s orbital uses two 2p orbitals

Alkyne: sp, where one 2s orbital uses one 2p orbitals Alkyne to form two identical sp orbitals with 2p2 2p3

Strongest intermolecular bonds in order?

1) H-bond

2) pd-pd (permanent dipole)

3) id-id (induced dipole-instantaneous dipole)

Highest to lowest boiling point in hydrogen molecules

H2O > HF > NH3

Because H2O can form more hydrogen bonds than HF and NH3 and strong hydrogen bonds present between water molecules.