Group 0 (noble gases) have full outer shells, so they are unreactive. Boiling points rise down the group.

Group 1 (alkali metals) have one outer electron, which they lose to form 1+ ions. With water they fizz, float and form a metal hydroxide and hydrogen:

sodium + water → sodium hydroxide + hydrogen
2Na + 2H₂O → 2NaOH + H₂

Reactivity increases down the group: the outer electron is further from the nucleus and more shielded, so it is lost more easily.

The halogens have seven outer electrons and gain one to form 1− ions. Reactivity decreases down the group (an electron is gained less easily further from the nucleus), and melting and boiling points rise.

A more reactive halogen displaces a less reactive one from a solution of its salt:

chlorine + potassium bromide → potassium chloride + bromine
Cl₂ + 2KBr → 2KCl + Br₂

Iodine cannot displace bromine or chlorine.

Compared with Group 1, transition metals such as iron, copper and nickel are harder, denser, have higher melting points and react much less. They form ions with different charges, coloured compounds, and are useful catalysts.