AS/A-level Chemistry: (Dative) Covalent Bonding

In AS/A-level Chemistry,

• A bond formed by a shared pair of electrons

• Note: “ – “ represents a shared pair of electrons

• Regular covalent bond:
  • Each atom involves in the bond donates one electron each to a shared pair
  • This shared pair represents one covalent bond
  • e.g. HCL = H Cl → H Cl = (H – Cl )
• Multiple bonds:
  • Double bond= Forming of 2 shared pairs of electrons between 2 atoms
  • Triple bond= Forming of 3 shared pairs of electrons between 3 atoms
  • e.g. O₂ = O O → O O = (O – O) 2 pairs
  • N₂ = N N → N N = (N – N ) 3 pairs
• Atoms DON’T bond covalently to try to obtain 8 electrons in their outer shell
• Atoms will try to make as many covalent bonds as they have electrons as their outer shell
• To do this, atoms will where possible promote electrons to higher sub levels within the same outer shell, to maximise the number of bonds they can make:

• Boron can only make 1 covalent bond BUT it has a fixed oxidation state of +3
• This tells us boron uses 3 electrons to make bonds

When boron forms compounds, it does this:

• One of the electrons in the lone pair is promoted to a vacant orbital in the “2p” sub level
• To form boron’s BONDING STATE configuration:
• Boron in its bonding state possesses:
  • 0 lone pair
  • 3 bonding electrons

In AS/A-level Chemistry,

• When a lone pair of electrons from one atom is donated into a vacant orbital of another atom
• Dative bond arises when one atom donates both electrons to a shared pair
• i.e. It involves the donation of lone pairs of electrons

• There are certain compounds, where 2 atoms are joined together by both regular covalent bonds and dative covalent bonds. E.g. Carbon monoxide(CO)

• Once a dative bond forms, it behaves identical to and is indistinguishable from a regular covalent bond in a compound
• i.e. We can treat dative bonds as if they were covalent bonds          

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