Group 1: The Alkali Metals

Each alkali metal has one outer electron

• Lithium (proton number 3): 2, 1
• Sodium (proton number 11): 2, 8, 1
• Potassium (proton number 19): 2, 8, 8, 1
• The lone outer electron is the only thing the atom needs to lose in order to react

Forming 1+ ions

• When a Group 1 atom reacts, it loses its single outer electron to form a 1+ ion (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺)
• The shell below becomes the new outermost shell — it is already full, so the ion has the noble gas configuration of the previous group 0 element

Why reactivity increases down the group

• Going from lithium down to caesium, one extra electron shell is added at each step
• The outer electron therefore sits further from the nucleus
• The attraction between the outer electron and the positive nucleus is weaker (more distance, and inner shells partly shield the nuclear charge)
• Less energy is needed to remove the outer electron, so the atom loses it more easily
• An atom that loses its outer electron more readily reacts more readily — so the metals get more reactive as you descend the group