Group 1 (Alkali Metals): soft, low density, low melting points. React vigorously with water → hydroxide + hydrogen. Reactivity increases down the group (outer electron further from nucleus, easier to lose).
Group 7 (Halogens): non-metals, diatomic molecules. Reactivity decreases down the group (harder to gain an electron). More reactive halogen displaces less reactive from its salt.
Group 0 (Noble Gases): full outer shells → unreactive. Boiling points increase down the group due to increasing intermolecular forces.