The Periodic Table - Group 1 (Alkali metals)

Group 1 elements, known as the Alkali Metals, include Lithium ($Li$), Sodium ($Na$), Potassium ($K$), Rubidium ($Rb$), Cesium ($Cs$), and Francium ($Fr$).

Electronic Configuration: All Group 1 atoms have a single electron in their outermost shell, denoted by the general configuration $ns^1$.

Physical Properties: They are soft (can be cut with a knife), have low densities (the first three float on water), and have relatively low melting and boiling points compared to other metals.

Reactivity Trend: Reactivity increases down the group. As the atomic radius increases, the distance between the nucleus and the outer electron increases, and the shielding effect of inner shells increases. This results in a lower first ionization energy, making it easier to lose the $e^-$.

Chemical Reactions: They react vigorously with water to produce a metal hydroxide ($MOH$) and hydrogen gas ($H_2$). The resulting solution is alkaline ($pH > 7$).

Flame Colors: When heated, they produce characteristic flame colors: $Li$ (red), $Na$ (yellow/orange), $K$ (lilac).

Trends in Physical Properties: Melting points and boiling points decrease down the group because the metallic bond weakens as the ionic radius of the $M^+$ cation increases.