Group 1 Elements – Alkali Metals

The Group 1 elements are called alkali metals: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). They all have one electron in their outer shell, which they easily lose to form +1 ions. This makes them very reactive metals.

Alkali metals are soft (can be cut with a knife), have low density (Li, Na, K float on water), and have relatively low melting points that decrease down the group. They are stored under oil to prevent reaction with air and moisture.

Reactivity increases down the group because the outer electron is further from the nucleus and more easily lost. Lithium reacts gently with water, sodium reacts vigorously, and potassium reacts so vigorously it often ignites the hydrogen gas produced.

With water: Alkali metals react vigorously with water to produce a metal hydroxide (an alkali, hence the name) and hydrogen gas. The general equation is: 2M + 2H₂O → 2MOH + H₂↑

With oxygen: Alkali metals burn in oxygen to form metal oxides. Sodium burns with a yellow flame: 4Na + O₂ → 2Na₂O. These oxides are basic and dissolve in water to form alkaline solutions.

With chlorine: Alkali metals react with chlorine to form white ionic salts called metal chlorides: 2Na + Cl₂ → 2NaCl. These reactions are vigorous and produce white smoke.

Flame tests can identify alkali metals: lithium gives a crimson red flame, sodium gives a golden yellow flame, and potassium gives a lilac flame. This is because each element emits light of a specific wavelength when heated.