Nature of Covalent & Dative Covalent Bonds (Oxford AQA International A Level Chemistry)

Covalent & Co-ordinate Bonding

• Covalent bonding occurs between two non-metals

• A covalent bond involves the electrostatic attraction between nuclei of two atoms and the bonding electrons of their outer shells

• No electrons are transferred but only shared in this type of bonding

Covalent bond formation

• Non-metals are able to share pairs of electrons to form different types of covalent bonds

• Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas

  • This makes each atom more stable

• A single covalent bond is formed from one pair of electrons and is represented by a single line

• Double and triple bonds can also form:

  • Double bonds consist of two pairs of electrons

  • Triple bonds consist of three pairs of electrons

Number of electrons in different covalent bonds

Examples of covalently bonded molecules

Chlorine, Cl₂

Hydrogen Chloride, HCl

Ammonia, NH₃

Methane, CH₄

Carbon dioxide, CO₂

Ethene, C₂H₄

Nitrogen, N₂

Coordinate covalent bonding 

• In simple covalent bonds, the two atoms involved share electrons

• Some molecules have a lone pair of electrons that can be donated to form a bond with an electron-deficient atom

  • An electron-deficient atom is an atom that has an unfilled outer orbital

• So both electrons are from the same atom

• This type of bonding is called dative covalent bonding or coordinate bonding

• An example with a dative bond is in an ammonium ion

  • The hydrogen ion, H⁺ is electron-deficient and has space for two electrons in its shell

  • The nitrogen atom in ammonia has a lone pair of electrons which it can donate to the hydrogen ion to form a dative covalent bond

The ammonium ion