How do alkali metals react with oxygen?

Alkali metals react with oxygen to form metal oxides, which are basic in nature.

Alkali metals, found in Group 1 of the Periodic Table, are highly reactive due to their single electron in the outermost shell. This makes them eager to participate in chemical reactions, particularly with oxygen. When alkali metals come into contact with oxygen, they react vigorously, often with a noticeable release of heat and light, to form metal oxides. These reactions are exothermic, meaning they release energy in the form of heat.

The general equation for this reaction is 4M + O2 → 2M2O, where M represents an alkali metal. The resulting product, M2O, is a metal oxide. These oxides are basic, meaning they react with acids to form salts and water, a property characteristic of all bases. For example, if sodium (Na) reacts with oxygen (O2), the resulting product is sodium oxide (Na2O).

The reactivity of alkali metals increases down the group. This means that lithium (Li), at the top of the group, is the least reactive with oxygen, while francium (Fr), at the bottom, is the most reactive. This increased reactivity is due to the increasing distance of the outermost electron from the nucleus as you move down the group, which makes it easier for the atom to lose this electron and react.

It's important to handle alkali metals with care. Due to their high reactivity, they can react explosively with oxygen, especially in larger quantities or when finely divided. For this reason, alkali metals are usually stored under oil to prevent them from coming into contact with oxygen in the air.