Atoms always try to have a full outer shell of electrons - in order to achieve this they will bond with other atoms
When atoms bond together they form molecules - those made of one type of atom are elements while those made of many types are compounds
Intramolecular Bonds
Atoms may join together by gaining and losing electrons (ionic bonding) or by sharing electrons (covalent bonding)
Ionic Bonds:
- Ionic bonding occurs between a metal and a non-metal
- The metal has a nearly empty outer shell and so loses electrons to form a positively charged cation
- The non-metal has a nearly full outer shell and so gains electrons to form a negatively charged anion
- The resulting charge of these two ions creates a strong electrostatic attraction between them - an ionic bond
Covalent Bonds:
- Covalent bonding occurs between two non-metals
- Because both atoms have a large number of electrons in their outer shell, it is not feasible to lose or gain so many and so they share
- The number of covalent bonds able to be formed reflects the number of missing electrons from the outer shell (e.g. carbon needs four electrons and so can form four covalent bonds)
- Because there is no ionic charge, covalent molecules are not as strongly attracted to each other as ionic molecules (covalent bonds are weaker)
Intermolecular Bonds
Atoms from one molecule may attract atoms from another molecule – these bonds are much weaker than intramolecular bonds
Hydrogen Bonds:
- The covalent sharing of electrons between atoms may not always be equal and will depend on:
- The number of protons in an atom (more protons equals a greater attraction for electrons)
- The number of electron shells in an atom (electrons at a further distance from the nucleus are less attracted to nucleus)
- Atoms that have a stronger affinity for electrons are said to have a higher electronegativity
- Covalently shared electrons will orbit closer to atoms with a higher electronegativity, resulting in a slight charge difference
- These molecules are polar and can form weak electrostatic associations with other polar molecules
- Polar associations between an H atom of one molecule and an F, O or N atom of another molecule are called hydrogen bonds
