Group 7 The Halogens KLASS.pptx

Halogen

1. The halogens Later

2. Group 7 The Halogens

3. Physical Properties Simple Molecular Structures Diatomic molecules Strong covalent b onds 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 Ionic Bonding 2Na + Cl 2 2NaCl Ca + F 2 CaF 2 Na + Cl - xo xx xx xx Ca 2+ F - xo xx xx xx F - xo xx xx xx

6. Examples b) Covalent Bonding HCl Cl 2

7. Reactivity decreases as you go down group 7 Reaction Conditions F 2(g) + H 2(g) → 2HF (g) Explosive even at -200 o C in the dark. Cl 2(g) + H 2(g) → 2HCl (g) Explosive in sunlight. S low in the dark. Br 2(g) + H 2(g) → 2HBr (g) 300 o C + Pt catalyst I 2(g) + H 2(g) → 2HI (g) Very slow at 300 o C with Pt catalyst

8. Group 7 – forming negative ions 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 REACTIVITY INCREASES Cl F

9. Halogen displacement reactions Miss Iodide Mr Sodium Sodium Iodide Miss Bromine + + Bromine Mr Sodium Sodium Bromide + Iodine Miss Bromide Miss Iodine 2NaI ( aq ) + Br 2( aq ) 2NaBr ( aq ) + I 2( aq ) Iodide oxidised Bromine reduced

10. Halogen displacement reactions Miss Potassium Mr Bromide Mr Chlorine + Miss Potassium Mr Bromine Mr Chloride Potassium Bromide + Chlorine Potassium Chloride + Bromine 2KBr ( aq ) + Cl 2( aq ) 2KCl ( aq ) + Br 2( 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