The Periodic Table: Group 1

The first group in the Periodic Table is known as the Alkali Metal group.
It includes elements such as Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr).
These metals have similar properties due to only having one electron in their outer electron shell.

Group 1 metals are highly reactive and never found in their pure form in nature, but instead are usually found as compounds.
Reactivity increases down the group. For instance, Potassium (K) is more reactive than Sodium (Na), which in turn is more reactive than Lithium (Li).
They have a strong tendency to lose their single outer electron in reactions to form positive ions (+1), known as oxidation.
They react vigorously with non-metals, particularly with Halogens (Group 7) and Oxygen, often resulting in violent reactions.

Group 1 metals are soft and can be cut with a knife.
They have low melting and boiling points, which decrease down the group.
They exhibit low density compared to other metals. Some of them, like Lithium (Li), will even float on water.

Alkali metals react with water producing a strong alkaline solution of a metal hydroxide and hydrogen gas.
The reactions are increasingly vigorous down the group resulting in more heat released, meaning that they can actually ignite the hydrogen produced.
For instance, the reaction of sodium with water could be represented as: 2Na + 2H2O -> 2NaOH + H2

Alkali metals react vigorously with halogens, resulting in salts known as metal halides.
For instance, the reaction of sodium with chlorine could be represented as: 2Na + Cl2 -> 2NaCl

The atomic radius increases down the group because an extra electron shell is added with each period.
The ionic radius also increases down the group, since the result of losing one electron does not significantly decrease the size of the ion, and each ion has one more electron shell than the one above it.