Question

what happens to the melting and boiling points down a group and across a period for metals and non-metals?

Answer 1

Across a period:

Melting point increases from group 1 to group 14 and then decreases. This because, from group 1 to group 14, metal and metalloids show metallic bonding, so they have higher melting point but Group 14 onwards, the increase in electron in p shell causes repulsion energy to dominate which makes bonds weaker within the atoms of the element and they have low melting points.


Boiling point also increases from group 1 to 14 and the decreases. Same as above.

Down the group:

Melting and boiling points decreases down the group. This is because, as we go down the group due to increase in size, the compactness of the element decreases, and it has more spacial structure with weak bonds. So, melting and boiling points decrease down the group.