Group 1 of the periodic table contains the alkali metals – a group of highly reactive elements with similar properties. All Group 1 elements have one electron in their outer shell, which makes them very reactive metals.

Elements in Group 1

💡 Reactivity increases as you move down the group.

Electron structure and reactivity

• All alkali metals have 1 outer shell electron
• They easily lose this electron to form a 1⁺ ion and gain a full outer shell
• As you go down the group:
  
  • The atomic radius increases
  • The outer electron is further from the nucleus
  • It is lost more easily → increased reactivity

Physical properties of alkali metals

Reactions with water

Alkali metals react with water to produce:

• A metal hydroxide (alkaline solution)
• Hydrogen gas

Word equation:

Alkali metal + water → metal hydroxide + hydrogen

Symbol equation example (sodium):

2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)

Observations:

💡 Reaction becomes faster and more vigorous down the group.

Reaction with chlorine

Alkali metals react vigorously with chlorine gas to form white metal chlorides.

Example:

2Na + Cl₂ → 2NaCl

These compounds are ionic and form white solids that dissolve easily in water.

Reaction with oxygen

Alkali metals react quickly with oxygen in air, forming a metal oxide.

• The shiny surface tarnishes as a dull oxide layer forms

Example:

4Li + O₂ → 2Li₂O

This is why alkali metals are stored under oil – to stop them reacting with air or moisture.