Chem 2 (Group 7)

Question 1

Properties of Group 7 elements

Answer 1

• most reactive non-metals
• 7 electrons in their outer shell
• often form metal halides with Group 1 and 2 metals.

Question 2

Why are they diatomic?

Answer 2

because they have two halogen atoms are covalently bonded together

Question 3

How are the molecules held together?

Answer 3

Van der Waals (temporary dipoles) is when the electron density is fairly symmetrical in a molecule but it’s always going to change so one side is going to be slightly more electronegative ($-) which induces a dipole to make a $+ in a neighboring molecule so although this is constantly changing it holds the molecules together.

Question 4

How does the Van der Waals affect boiling points?

Answer 4

Fluorine is a gas at room temperature because it doesn’t take much energy to overcome the bonds. Chlorine has permanent dipoles so it going to have stronger intermolecular forces but still is a small molecules. Iodine and bromine are larger molecules so have an increased number of Van der Waals and require a lot more energy to break. Iodine is the highest (solid at room temp).

Question 5

What 2 things decrease as you go down Group 7?

Answer 5

• volatility (tendency to turn into a gas)

- Electronegativity

Question 6

What is the pattern of electronegativity?

Answer 6

Fluorine is the most electronegative because it is the smallest atom so its nucleus will be close to the other atom’s nucleus with little shielding so the power is going to be strong. Cl has one more shell of electrons so increased shielding from the nucleus, so is going to be slightly less. As the size of the molecule increases, the less electronegative it becomes.
F>Cl>Br>I

Question 7

Oxidising abilities?

Answer 7

Either they share electrons in a covalent bond or they accept an electron and form a negative ion in an ionic compound like sodium chloride.
Their ability to accept these ions makes them a good oxidising agent.
Order: F2>Cl2>Br2>I2

Question 8

Chlorine + potassium bromide = ?

Answer 8

Cl2 + KBr > KCl + Br2

Cl2 + 2Br- > 2Cl- + Br2

Question 9

half equations for Chlorine + potassium bromide = ?

Answer 9

Cl2 + 2e- > 2Cl- (reduced)

2Br- > Br2 + 2e- (oxidised)

Question 10

Which halogen atoms displace which?

Answer 10

Fluroine displaces all of them
Chlorine displaces bromine
Bromine displaces iodine
Chlorine and bromine displace iodine

Question 11

If halogen atoms are good oxidising agents.and accept electrons then halide ions?

Answer 11

are good reducing agents and donate electrons

Question 12

pattern of reducing abiltiy of halide ions down group 7?

Answer 12

Increases down group 7

F- > Cl- > Br- >I-

Question 13

What are halides?

Answer 13

Halogen compounds with ionic bonding

Question 14

When sodium halides react with conc. sulfuric acid..?

Answer 14

• sodium hydrogen sulfate

- matching hydorgen halude e.g. HBr-, HCl- ect

Question 15

H2S04 + KF/NaF

Answer 15

H2S04 + KF > K2S04 + 2HF
no redox reaction
fluorine doesn’t reduce halide ions

Question 16

H2S04 + NaCl…?

Answer 16

H2S04 + NaCl > NaHS04 + HCl
no redox reaction
Chlorien doesn’t reduce halide ions

Question 17

H2S04 + NaBr..> 1st reaction

Answer 17

H2S04 + NaBr > NaHS04 + HBr

no redox reaction

Question 18

H2S04 + NaBr..> 2nd reaction

Answer 18

2Br- > Br2 + 2e-
Bromide ions are oxidised (lose electrons)
S04 (2-) + 2e- > S02
Sulfate ions are reduced (gain electrons)

Question 19

colour of bromine

Answer 19

yellowy liquid

Question 20

H2S04 + NaI..? 1streaction

Answer 20

H2S04 + NaI > NaHS04 + HI

no redox reaction

Question 21

H2S04 + NaI..? 2nd reaction

Answer 21

2HI + H2S04 > S02 + 2H20 + I2
2I- > I2 + 2e- (iodide iions are oxidised-lose electrons)
S04 (2-) + 2e- > S02 (gain electrons-reduced

Question 22

H2S04 + NaI..? 3rd reaction

Answer 22

6HI + H2S04 > S + 4H20 + 3I2
2I- > I2 + 2e- (oxidised)
S04 (2-) + 6e- > S

Question 23

H2S04 + NaI..? 4th reaction

Answer 23

HI + H2S04 > H2S + H20 + I2
2I- > I2 2e– (oxidised)
S04 (2-) + 8e- > H2S

Question 24

products of conc h2S04 and iodide?

Answer 24

• iodine (violent fumes)
• S02 is colourless
• H2S is pungent

Question 25

Reacion of halide ions with acidified silver nitrate solution?

Answer 25

Ag+ + F- > AgF (water-soluble)
Ag + + Cl- > AgCl ( white precipitate of silver chloride)
Ag+ + Br- > AgBr ( cream precipitate of silver bromide)
Ag+ + I- > AgI (yellow precipitate of silver iodide)

Question 26

Reactions of halide ions with dilute aqueous ammonia/concentrated aqueous ammonia?

Answer 26

AgF ( no precipitate)
AgCl dissolves in dilute aqueous ammonia
AgBr - sparingly (slightly) soluble in dilute ammonia but dissolves properly in concentrated ammonia (or dissolves slightly)
AgI - insoluble in concentrated ammonia (wyellow precipitate turns white)

Question 27

Chlorie is used to treat water like in swimming pools (redox reaction to HOCl)…?

Answer 27

Cl2 + H20 > HOCl + HCl
Cl2 + e- > HCl
Cl2 > HOCl + e-

Question 28

HCl splits into..?

Answer 28

H+ + Cl-

Question 29

HOCl dissociates into ..?

Answer 29

HOCl (reversible) >< H+ + ClO-

Question 30

Cl0- (chlorate l ion) and H0Cl (chloric v acid) is useful for..?

Answer 30

killing pathogens

Question 31

Reaction of chlorine with cold, diluted sodium hydroxide (and ionic equation)

Answer 31

Cl2 + 2NaOH > NaCl0 + NaCl + H20

Cl2 + 2OH- > Cl0- + Cl- + H20

Question 32

Use of NaCl0?

Answer 32

bleach

Question 33

Reactions of halide ions with HN03?

Answer 33

AgCl = white ppt
AgBr = Cram/white ppt
AgI = white precipitate turns yellow again