6. Periodic trends in melting and boiling points.

Question 1

periodicity- what are the reasons for the trends in melting and boiling points as you go across a period in periods two and three?

Answer 1

as you go across a period, the type of bonding between the atoms of an element and type of structure changes.

Question 2

Metals (Li and Be, Na, Mg, and Al)-
why do the melting and boiling points increase across the period?

Answer 2

-Due to the metal-metal bonds getting stronger.
-This is because the metal ions have a greater charge, an increase in the number of delocalised electrons, and a decreasing ionic radius.
-This all leads to a higher charge density, which attracts the ions together more strongly.

Question 3

Giant Covalent structures (B,C and Si)-
why do they have the highest melting and boiling points in their periods?

Answer 3

Because they have strong covalent bonds linking all their atoms together and so a lot of energy is needed to break these bonds.

Question 4

Simple molecular structures (N2,O2,F2, and , P4, S8, Cl2)-
why do they have low melting and boiling points?

Answer 4

Though the covalent bonds between the atoms in a molecule are very strong, the melting and boiling points depend upon the strength of the induced dipole-dipole forces between their molecules.
These forces are weak and easily overcome.

Question 5

What about the nobal gases (Ne and Ar)?

Answer 5

They have the lowest melting and boiling points because they exist as individual atoms, being monatomic, which results in very weak induced dipole-dipole forces.