Group 1, 7 and 8 trends
1. Group 1 (Alkali Metals) – Trends
Elements: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs)
Key Trends Down Group 1
Atomic radius increases ↓(More electron shells added)
Reactivity increases ↓(Outer electron is farther from nucleus, easier to lose)
Melting point decreases ↓
Density generally increases ↓
They all form +1 ions
Very reactive with water (reaction becomes more violent down the group)
2. Groups in the Periodic Table (Overview)
Groups = vertical columns
Elements in the same group have the same number of outer-shell electrons
This gives them similar chemical properties
Examples:
Group 1 → 1 outer electron
Group 7 → 7 outer electrons
Group 8 (Group 0) → full outer shell
3. Atomic Structure of Group 1 Elements
All Group 1 elements have:
1 electron in the outer shell
They lose 1 electron to form +1 ions
Electron Configurations
Lithium: 2,1
Sodium: 2,8,1
Potassium: 2,8,8,1
Why they are reactive:That single outer electron is easy to lose.
4. Group 7 (Halogens) – Trends
Elements: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I)
Trends Down Group 7
Reactivity decreases ↓
Atomic radius increases ↓
Melting & boiling points increase ↓
Colour becomes darker ↓
They form –1 ions
5. Atomic Structure of Group 7 Elements
All Group 7 elements have:
7 electrons in the outer shell
They gain 1 electron to form –1 ions
Electron Configurations
Fluorine: 2,7
Chlorine: 2,8,7
Bromine: 2,8,18,7
Iodine: 2,8,18,18,7
Why reactivity decreases: Outer shell is farther from nucleus, harder to attract an electron.
6. Group 8 (Group 0 / Noble Gases) – Trends
Elements: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe)
Trends
Very unreactive
Boiling points increase ↓
Density increases ↓
Exist as single atoms (monatomic gases)
7. Atomic Structure of Group 8 Elements
All Group 8 elements have:
Full outer electron shell
Do not gain or lose electrons
Electron Configurations
Helium: 2
Neon: 2,8
Argon: 2,8,8
Krypton: 2,8,18,8
Why they are unreactive:Their outer shell is already full → stable