[vrai]

can anyone explain to me the trends of melting points & boiling point trends on the periodic table?
I need this asap!!!!!!!!!!!!!!! thanks

[Byrne]

Melting and boiling points increase with stronger intermolecular attractions.  The stronger these attractions are, the more energy required to overcome them and the higher the element or compound's melting/boiling point will be.

[plu]

Speaking of melting and boiling points...
Put the following substances in order of increasing melting point: Na, Al, Si, S₈.
The answer given by the source is Na < S₈ < Al < Si.
I don't understand how this order was deduced  

[Donaldson Tan]

Group I metals are known to exhibit low melting point. This is due to very weak metallic bonding.

There is significant intermolecular attraction between the S8 molecules, thus it has a higher melting point than Na. However, its structure is simple molecular, unlike that of Si.

Si exhibits macromolecular structure. Melting Si requires overcoming the covalent bond between the Si atoms, and therefore Si exhibits a very high melting point.

Al has a high melting point due to strong its strong metallic bonding. Each Al atom contributes 3 electrons to the 'sea' of delocalised electrons, thus forming a cationic lattice of Al3+ ions. This means there is strong attraction between the cations and the delocalised electrons, thus strong metallic bonding.