CIE IGCSE Chemistry

Revision Notes

3.3 Molecules & Covalent Bonds

Single Covalent Bonds

Covalent compounds

  • Covalent compounds are formed when electrons are shared between atoms
  • Only non-metal elements participate in covalent bonding
  • As in ionic bonding, each atom gains a full outer shell of electrons
  • When two or more atoms are chemically bonded together, we describe them as ‘molecules’

 

Covalent bonding in non-metals, IGCSE & GCSE Chemistry revision notesCovalent bonding in non-metals

 

Hydrogen:

Dot-&-cross-Hydrogen_, IGCSE & GCSE Chemistry revision notes 

 

Chlorine:

Dot-&-cross-Chlorine_, IGCSE & GCSE Chemistry revision notes

 

H2O:

Dot & cross Water, IGCSE & GCSE Chemistry revision notes

 

CH4 (methane):

Dot & cross Methane, IGCSE & GCSE Chemistry revision notes

 

NH3 (ammonia):

Dot & cross Ammonia, IGCSE & GCSE Chemistry revision notes 

HCl:

Dot & cross Hydrochloric-Acid, IGCSE & GCSE Chemistry revision notes 

Ionic & Covalent Compounds

  • Ionic compounds
    • Have high melting and boiling points so ionic compounds are usually solid at room temperature
    • Not volatile so they don’t evaporate easily
    • Usually water-soluble as both ionic compounds and water are polar
    • Conduct electricity in molten state or in solution as they have ions that can move and carry a charge
  • Covalent compounds
    • Have low melting and boiling points so covalent compounds are usually liquids or gases at room temperature
    • Usually volatile which is why many covalent organic compounds have distinct aromas
    • Usually not water-soluble as covalent compounds tend to be nonpolar but can dissolve in organic solvents
    • Cannot conduct electricity as all electrons are involved in bonding so there are no free electrons or ions to carry the charge
Extended Only

Electron Arrangement in Complex Covalent Molecules

Nitrogen:

Dot & cross Nitrogen, IGCSE & GCSE Chemistry revision notes 

C2H4 (ethene):

Dot-&-cross-Ethene_, IGCSE & GCSE Chemistry revision notes 

CH3OH (methanol):

Dot & cross Methanol, IGCSE & GCSE Chemistry revision notes

 

CO2:

Dot-&-cross-Carbon-Dioxide_, IGCSE & GCSE Chemistry revision notes

Extended Only

Melting & Boiling Points of Ionic & Covalent Compounds

  • Ionic compounds have high melting and boiling points
  • This is because the oppositely charged ions in the lattice structure are attracted to each other by strong electrostatic forces which hold them firmly in place
  • Large amounts of energy are needed to overcome these forces so the m.p. and b.p. are high
  • Simple covalent substances, such as carbon dioxide and methane, have very strong covalent bonds between the atoms in each molecule, but much weaker intermolecular forces between individual molecules
  • When one of these substances melts or boils, it is these weak intermolecular forces that break, not the strong covalent bonds
  • Less energy is needed to break the molecules apart, so they have lower m.p. and b.p. than ionic compounds

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.
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