group 7

Question 1

what are the physical properties of group 7?

Answer 1

● fluorine is a pale yellow gas (F2)

● chlorine is a green / yellow gas (Cl2)

● bromine is an orange / brown liquid (Br2)

● iodine is a grey / black solid (I2)

Question 2

what happens to atomic radius down group 7?

Answer 2

● increases down group

● extra filled electron shell

Question 3

what happens to electronegativity down group 7?

Answer 3

● decreases down group

● larger atomic radius

● more shielding

● weaker attraction of outer e- to positive nucleus

Question 4

what happens to melting and boiling point down group 7?

Answer 4

● increases down group

● atoms get larger

● more electrons

● stronger van der waals forces

Question 5

how to identify halide ions?

Answer 5

● with silver (Ag+) ions

● all metal halides (except fluorides) react with Ag+ ions in solution

● forms a precipitate of insoluble silver halide

● X- (aq) + Ag+ (aq) -> AgX(s)

● chlorine ions forms a white AgCl precipitate

● bromine forms a pale cream AgBr precipitate

● iodine forms a pale yellow AgI precipitate

Question 6

what is the method for identifying the halide ions?

Answer 6

● 1. add dilute nitric acid (HNO3) to halide solution

● to remove any soluble carbonate or hydroxide impurities

● if CO3 2+ / carbonate ions are present effervescence is observed

● CO3 2+ (aq) + 2H+ (aq) -> CO2 (g) + H2O(l)

● OH- (aq) + H+ -> H2O

● we have to remove any impurities as carbonate ions form silver carbonate or hydroxide ions can form insoluble silver hydroxide so they would interfere with the test

● 2. add a few drops of silver nitrate solution and observe precipitate that form

● distinguishing between precipitates can be difficult so dilute and concentrated ammonia can help