Electronic Configuration & Reactivity

Electronic configuration

Arrangement of electrons in shells

Outer shell electrons

Determine chemical reactivity

Group number

Equals number of electrons in outer shell

Period number

Equals number of electron shells

Metals reactivity pattern

More reactive down a group

Reason metals become more reactive down group

Outer electron further from nucleus, easier to lose

Non‑metals reactivity pattern

Less reactive down a group

Reason non‑metals become less reactive down group

Harder to gain an electron as shells increase

Group 1 metals

Lose 1 electron to form +1 ions

Group 7 halogens

Gain 1 electron to form –1 ions

Why Group 1 metals are very reactive

Only one electron to lose

Why Group 7 halogens are very reactive

Only need one electron to gain

Noble gases (Group 0)

Unreactive due to full outer shell

Why full outer shell = unreactive

No need to gain or lose electrons

Example: sodium (2,8,1)

Loses 1 electron easily → very reactive

Example: chlorine (2,8,7)

Gains 1 electron easily → very reactive

Trend in Group 1

Reactivity increases down the group

Trend in Group 7

Reactivity decreases down the group