Physical Properties of Halogens

Halogens exist as simple molecules with two atoms joined by a single covalent bond. This means each halogen atom shares electrons with another to achieve a full outer shell.

As you move down Group 7 from fluorine to iodine, both melting and boiling points increase. This happens because the molecules become larger, which strengthens the intermolecular forces between them. These forces are the weak attractions between molecules that must be overcome during melting or boiling.

Science Insight: When a halogen melts or boils, only the intermolecular forces break - not the strong covalent bonds holding the two atoms together in each molecule!

It's important to remember that more energy is needed to overcome these forces as the halogen atoms get larger, which explains why iodine has much higher melting and boiling points than fluorine.

Chemical Properties of Halogens

Halogens all have 7 electrons in their outer shell, which explains their similar chemical behaviours. They're eager to gain one more electron to achieve a full outer shell, making them quite reactive.

When halogens react with metals, they form salts. For example, when sodium (a metal) reacts with chlorine (a halogen), they produce sodium chloride - common table salt! The general equation is: metal + halogen → metal halide.

A key trend in Group 7 is that reactivity decreases as you move down the group. This means fluorine at the top is the most reactive halogen, while iodine at the bottom is the least reactive.

Remember This: The pattern "reactivity decreases down Group 7" is commonly tested in exams - it's the opposite trend to what happens in Group 1!