The Halogens (group 7) Flashcards
What do the halogens look like?
F2: almost colourless gas
Cl2: pale green gas
Br2: red-brown liquid
I2: grey-black solid
Trends down the group of halogens
Colour: gets darker
MP and BP: increase
Volatility: decrease, switch from gas to liquid (intermolecular bonds get stronger)
Solubility: not very soluble
How do all halogens exist?
As diatomic molecules, with a covalent bond
Chemical properties of halogens
They must gain one electrons to achieve a noble gas configuration, therefore they are all oxidising agents.
Oxidising power increases going up the group.
Why does oxidising power increase up the group in halogens?
The smaller the halogen atom, the better it is at gaining an electron. The atom has fewer shells so the incoming electron is closer to and less shielded from the positive nucleus.
What kind of compounds do halogens form with metals and non-metals?
metals The halogens form ionic compounds. They fully gain an extra electron, becoming halide ions.
non-metals the halogens share electrons, forming a covalent bond.
What does Chlorine look like as halide ions, halogens in (aq) and halogens in an organic solvent?
halide ions: colourless
halogens (aq): very pale green
halogens in organic: pale green
What does Bromine look like as halide ions, halogens in (aq) and halogens in organic solvents?
halide ions: colourless
halogens (aq): orange
halogens in organic: brown
What does iodine look like as halide ions, halogens in (aq) and halogens in organic solution?
halide ions: colourless
halogens (aq): brown
halogens in organic: top layer purple
Why do you shake halogens with an organic solvent such as cyclohexane?
If a reaction occurs there will be a colour change, to see this more clearly shake the mixture with an organic solvent. Organic solvents and water are immisable so 2 layers will form.
Halogen molecules are non-polar so dissolve better in the upper organic layer giving a characteristic colour which is more distinctive.
What happens when you react Cl- (chloride) with AgNO3?
Ppt: white
Name: AgCl, silver chloride
Ionic: Ag+ + Cl- => AgCl
What happens when you react Br- (bromide) with AgNO3?
Ppt: cream
Name: AgBr, Silver bromide
Ionic: Ag+ + Br- => AgBr
What happens when you react I- (iodide) with AgNO3?
Ppt: yellow
Name: AgI, silver iodide
Ionic: Ag+ + I- => AgI
What happens when you react F- (fluoride) with AgNO3?
Nothing as AgF is soluble
What’s a further test to confirm the presence of Cl, Br and I? (When reacted with AgNO3)
AgCl: completely redissolves
AgBr: partially redissolves
AgI: doesn’t redissolve
