Periodicity; Melting and Boiling Point

• Melting point decreases DOWN THE GROUP.
• Larger ionic radius down the group
• increase in shielding
• Weaer attraction between delocalised electrons to positive ions

Across the period:

• Melting point increases
• More delocaised electrons, ions
• greater charge
• Greater attraction between delocalised electrons and positive ions 

DIAMOND,GRAPHITE AND SILICON DIOXIDE:

• Very high melting and boiling point
• Lots of energy…