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:
a) Ionic bonding – Accept one electron from
a metal atom to become a halide ion with
a -1 charge.
b) Covalent bonding – Form one covalent
bond with another non-metal.
7. Reactivity decreases as you go down
group 7
Reaction Conditions
F2(g) + H2(g) → 2HF(g)
Explosive even at
-200oC 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 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
R
E
A
C
T
I
V
I
T
Y
I
N
C
R
E
A
S
E
S
Cl
F
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!
