Module 2 - Covalent Bonding

Question 1

Define covalent bonding.

Answer 1

Covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 2

When does covalent bonding occur?

Answer 2

Covalent bonding occurs between atoms in:

• non-metallic elements (H2, O2)
• compounds of non-metallic element (H2O, CO2)
• polyatomic ions (NH4^+)

Question 3

Orbital overlap:

Answer 3

• A covalent bond is the overlap of atomic orbitals, each containing one electron, to give a shared pair of electrons.
• The shared pair of electrons is attracted to the nuclei of both the bonding atoms.
• The bonded atoms often have outer shells with the same electron structure as the nearest noble gas.

Question 4

More on covalent bonds:

Answer 4

• In a covalent bond, the attraction is localised, acting solely between the shared pair of electrons and the nuclei of the two bonded atoms.
• The result can be a molecule.
• A molecule is the smallest part of a covalent compound that can exist whilst retaining the chemical properties of the compound.

Question 5

Single covalent bonds: Dot-and-cross diagrams

Answer 5

=in covalent bonding electrons are shared.
=in ionic bonding electrons are transferred.
-Dot-cross diagrams allows the origin of each electron and the structure of the molecule to be shown clearly.

Question 6

Single covalent bonds: Displayed formula

Answer 6

• Paired electrons that are not shared are called lone pairs. These can also be added to displayed formulae.
• carbon forms 4 bonds.
• nitrogen forms 3 bonds.
• oxygen forms 2 bonds.
• hydrogen forms 1 bond.

Question 7

Special cases:

Answer 7

Boron - 6 outer electrons = BF3 (only 3 outer shell electrons can be paired)
Phosphorus - 5 outer electrons = PF3, PF5
Sulfur - 6 outer electrons = SF2, SF4, SF6
Chlorine - 7 outer electrons = ClF, ClF3, ClF5, ClF7

Question 8

More on sulfur’s bonding:

Answer 8

SF2 = two unpaired electrons, two bonds possible.
SF4 = four unpaired electrons, four bonds possible.
SF6 = six unpaired electrons, six bonds possible.

Question 9

Double covalent bonds:

Answer 9

-In a double bond, the electrostatic attraction is between two shared pairs of electrons and the nuclei of the bonding atoms. e.g. O=O, O=C=O

Question 10

Triple covalent bonds:

Answer 10

-In a triple bond, the electrostatic attraction is between three shared pairs of electrons and the nuclei of the bonding atoms. e.g. N≡N, H-C≡N

Question 11

Dative covalent bonds:

Answer 11

• A dative covalent or coordinate bond is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only.
• In a dative covalent bond the shared electron pair was originally a lone pair of electrons on one of the bonded atoms.
  e. g. NH3 (with lone pair) + H^+ ion = NH4^+
• A dative covalent bond is represented by an arrow.