Get premium membership and access revision papers with marking schemes, video lessons and live classes.

Processing. Please wait.

The trend of melting and boiling points across period three

Answer Text:
The trend of Melting and boiling points across period 3
- Sodium, magnesium and aluminium have very high melting and boiling points.
Reason:
- They have giant metallic structures with strong metallic bonds which need a lot of energy to break.
- The boiling and melting points increase from sodium to aluminium.
Reason:
- As you move across the period from sodium to aluminium, the nuclear charge increases while the energy levels remain the same hence decrease in atomic radius; the smaller the atomic radius (for metals) the stronger the metallic bonds.
- Silicon, though a non-metal also has a very high melting and boiling points.
Reason:
- Silicon has a giant atomic structure with strong covalent bonds throughout the structure, which need a lot of heat energy to break.
- Phosphorus, Sulphur, Chlorine and argon have low melting and boiling points.
Reason:
- They all have molecular structures with strong covalent bonds between the atoms (except in argon) but weak van der waals forces between the
molecules which are easy to break.
- Note that argon exist as atoms and thus a monoatomic molecule.
- The melting and boiling points decreases from phosphorus to argon.
Reason.
- As we move across the period from phosphorus to argon, the size of the atoms decreases leading to smaller atoms and hence molecules, which lead to
decrease in the strength of the van der Waals (across the period)
Note:
- Phosphorus and sulphur exists as solids at room temperature while chlorine and argon exists as gases at room temperature.
Reason: phosphorus and sulphur have giant molecular structures while chlorine and argon have simple molecular structures.