Covalent bond

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A covalent bond is a bond in which at least two electrons are shared between atoms. A pair of electrons may be donated from one atom to another forming a dative covalent bond. A covalent bond holds atoms together as it is the attraction of the negatively charged electrons to the positively charged nucleus of both atoms[1].

Contents

Properties of Covalently Bonded Molecules

Covalently bonded molecules have relatively low melting points despite the high strength of the bond due to the weak intermolecular forces holding the solids together. The intermolecular forces can be strengthened when there is a difference in electronegativity between the atoms making the bond polar. They don’t usually conduct electricity as the electrons are locked in the bond and aren’t free to flow[2].

Types of Covalent Bond

Single Bonds

Single bonds are formed from the ‘head on’ overlap of orbitals in the outer shell of the atom in a process called hybridisation which forms a sigma bond. Usually, one electron is given from each atom but sometimes a pair will be donated from one atom to another with an empty outer orbital. This is called a dative covalent bond. Single bonds are free to rotate[3].

Double Bonds

Double bonds are formed from the overlap of p-orbitals which overlap sideways. The pi bonds are weaker than sigma bonds but are used together to form the double bond. When the sigma bonds form the p-orbitals are pulled closer together and practically touch[4].

References

  1. Structure and Bonding, Jack Barrett, 2001, Chapter 3, page 35, 3.1- Ionic, Covalent and Coordinate (or Dative) Bonding.
  2. Single Bonds Jim Clark 2000 https://www.chemguide.co.uk/atoms/bonding/covalent.html#top (modified January 2014)
  3. Single Bonds Jim Clark 2000 https://www.chemguide.co.uk/atoms/bonding/covalent.html#top (modified January 2014)
  4. Double Bonds Jim Clark 2000 https://www.chemguide.co.uk/atoms/bonding/doublebonds.html (modified September 2012)
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