How do melting and boiling points vary in a (a) period and (b) group in periodic table?

Explanation

To understand how melting and boiling points vary in a period and a group in the periodic table, we can break down the explanation into two parts: (a) variation in a period and (b) variation in a group.

### (a) Variation in a Period:
1. **Initial Increase**: As we move from left to right across a period in the periodic table, the melting and boiling points generally increase. This is because the number of electrons in the outer shell increases, leading to stronger metallic or covalent bonding.

2. **Stronger Bonding**: The increase in bonding strength is due to the increase in nuclear charge (more protons) which attracts the electrons more strongly, resulting in stronger interactions between atoms.

3. **Peak and Decrease**: However, after reaching a certain point (usually around the transition metals), the melting and boiling points start to decrease. This is due to increased electron-electron repulsion in larger atoms, which can weaken the overall bonding.
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