Group 1 and Group 7

Group 1 - The Alkali Metals

Group 1 elements are known as alkali metals, comprising of lithium, sodium, potassium, rubidium, caesium and francium.
These metals are very reactive and hence are never found in their elemental form in nature, always bonded with other elements.
Across the period from lithium to francium, the alkali metals become more reactive. This is due to the increasing distance between the nucleus and the outer electron.
Alkali metals have one electron in their outer shell, leading to similar characteristics and reactivity.
When reacting with non-metals, Group 1 elements form ionic compounds.
Group 1 elements react vigorously with water to produce alkaline solutions, hence the name alkali metals.
The solutions produced when alkali metals react with water produce hydrogen gas.

Group 7 - The Halogens

Halogens include fluorine, chlorine, bromine, iodine and astatine, making up Group 7 in the periodic table.
Halogens are non-metals and are found in all three states of matter at room temperature: Fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
They have seven electrons in their outer shell, which makes them very reactive.
The reactivity of halogens decreases down the group, with fluorine being the most reactive and astatine the least reactive.
Halogens can form salts with metals and are known to gain one electron during reactions to achieve a full outer electron shell.
They form diatomic molecules (molecules made up of two atoms) due to their high reactivity.

Remember to focus on understanding the properties and trends of each group. Understanding why these trends occur will help explain and predict the behaviour of these elements.