1. The halogens
Later

2. Group 7 The Halogens

3. Physical Properties Simple Molecular Structures
Diatomic molecules
Strong covalent bonds
Weak intermolecular forces
Low melting and boiling points
Poor conductors of heat and electricity
Melting point and boiling point
increase as you go down the group.

4. Chemical Properties of the Halogens
All have 7 electrons in their outer shell.
They all want to gain one more electron for a full outer shell. There are two ways they can do this:
Ionic bonding – Accept one electron from a metal atom to become a halide ion with a -1 charge.
Covalent bonding – Form one covalent bond with another non-metal.

5. Examples + - - Na Cl F 2+ Ca - F Ionic Bonding 2Na + Cl2 2NaCl
Ca + F CaF2 + xo - xo - Na Cl xx xx F xx xx xx 2+ xx Ca xo - F xx xx xx

6. Examples
b) Covalent Bonding
HCl
Cl2

7. Reactivity decreases as you go down group 7
Reaction
Conditions
F2(g) + H2(g) → 2HF(g)
Explosive even at oC in the dark.
Cl2(g) + H2(g) → 2HCl(g)
Explosive in sunlight. Slow in the dark.
Br2(g) + H2(g) → 2HBr(g)
300oC + Pt catalyst
I2(g) + H2(g) → 2HI(g)
Very slow at 300oC with Pt catalyst

8. Group 7 – forming negative ions
REACTIVITY INCREASES F
Reactivity decreases as you go down the group.
In larger atoms the outermost electrons are further from the nucleus.
This makes it harder to gain an electron as it will be less strongly attracted to the nucleus Cl

9. Halogen displacement reactionsMr
Sodium
Miss
Iodide +
Miss
Bromine Mr
Sodium
Miss
Bromide
Miss
Iodine
Sodium Iodide +
Bromine
Sodium Bromide
+ Iodine
2NaI(aq) +
Br2(aq)
2NaBr(aq)
I2(aq)
Iodide oxidised
Bromine reduced

10. Halogen displacement reactions
Miss
Potassium Mr
Bromide + Mr
Chlorine
Miss
Potassium Mr
Chloride Mr
Bromine
Potassium Bromide +
Chlorine
Potassium Chloride
+ Bromine
2KBr(aq) +
Cl2(aq)
2KCl(aq)
Br2(aq)
Bromide oxidised
Chlorine reduced

11. What if we add fluorine to aqueous potassium chloride?
Fluorine is more reactive than chlorine so would displace chloride from it’s salt.
However, fluorine is so reactive it would instantly react with the water before it got to the chloride ions!

12. Cl F