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Chemistry > Group 7 > Flashcards

Group 7 Flashcards

1
Q

Explain the trend in boiling point of group 7:

A
  • There are Van der Waals forces between molecules
  • The molecules get larger as you go down the group as there’s more electrons
  • Therefore there’s stronger Van Der Waals forces between molecules
  • So there’s more energy required to overcome the intermolecular forces
  • Therefore the boiling point increases
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2
Q

Explain the trend in atomic/ionic radius in group 7:

A
  • Number of filled shells increases so the shielding increases
  • Forces of attraction between the nucleus and outer electrons decreases
  • Therefore atomic radius increases
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3
Q

Explain the trend in electronegativity in group 7:

A
  • Shielding increases
  • Nuclear charge increases
  • Atomic radius increases
  • Forces of attraction between nucleus and outer electrons decreases
  • Therefore, electronegativity decreases
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4
Q

Explain the trend in reactivity in group 7:

A
  • Shielding, atomic radius increases
  • Forces of attraction between the nucleus and outer electrons decreases
  • It’s harder to gain an electron
  • Reactivity decreases
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5
Q

What does oxidising power mean?

A

How good it is at accepting electrons.
(An oxidising agent is the one that’s reduced).

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6
Q

Predict and explain the trend in oxidising power of the halogens:

A

(Strongest) F2 > Cl2 > Br2 > I2 (Weakest)

It’s essentially the same as reactivity.

  • Shielding increases
  • Atomic radius increases
  • Forces of attraction between nucleus and outer electrons decreases
  • Harder to accept electrons so their oxidising power decreases
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7
Q

Describe the appearance of chlorine gas and chlorine water

A

Pale yellow green gas
Very pale green solution, often colourless

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8
Q

Describe the appearance of bromine water

A

Orange-brown liquid
A gas can form brown fumes

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9
Q

Describe the appearance of Iodine:

A

Brown solution/ Black solid

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10
Q

Describe the appearance of flourine:

A

Pale yellow gas

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11
Q

Describe and explain the trend of reducing powers of halide ions:

A
  • Increases
  • More shells, more shielding, atomic radius increases
  • Weaker forces of attraction between nucleus and outer electrons
  • So it’s easier to lose those electrons
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12
Q

Why does F- not act as a reducing agent?

A
  • Fewer shells/ little shielding
  • Small ionic radius
  • Very strong forces of attraction between nucleus and outer electrons
  • Requires a lot of energy to lose those electrons
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13
Q

Concentrated H2SO4 can be further reduced by which halide ions?

A

Bromide ions
Iodide ions

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14
Q

Why can’t chlorine reduce sulfuric acid?

A

It’s not a strong enough reducing agent

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15
Q

What can bromide ions reduce sulfuric acid into?

A

SO2

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16
Q

What can iodide ions reduce sulfuric acid into?

A

SO2
S
H2S

17
Q

What are the observations when bromide ions reduce sulfuric acid into SO2?

A
  • Brown fumes of Br2
  • SO2 is colourless (There’s no observation)
18
Q

What are the observations when iodide ions reduce sulfuric acid into S?

A
  • Black solid Iodine
  • S is a yellow solid
19
Q

What are the observations when iodide ions reduce sulfuric acid into sulfur?

A

S = yellow solid
I2 = black solid

20
Q

What are the observations when iodide ions reduce sulfuric acid into H2S?

A

Bad egg smell (H2S)
Black solid = I2

21
Q

When answering exam questions on testing for halides, what should you be careful of?

A

In exam questions, they often start with solids. So make sure the first step in a method is to add water to make a solution.

22
Q

How do we test for halides?

A
  • Place a solution of the halide in a test tube, 5cm3
  • Add 1cm3 dilute nitric acid. This removes any other ions that could give a precipitate with silver nitrate.
  • Add silver nitrate solution
  • White, cream or yellow precipitate formed
  • treat any precipitate with dilute ammonia solution
  • if precipitate still exists, add concentrated ammonia
23
Q

Which halide makes a white precipitate?

A

Chloride

24
Q

Which halide gives a cream precipitate?

A

Bromide

25
Q

Which halide gives a yellow precipitate?

A

Iodide

26
Q

Why do we use nitric acid and not something like HCL?

A

HCL would react with the silver and precipitate.

27
Q

What do you observe when you add:
- dilute NH3
- Concentrated NH3

to Agcl?

A

AgCl dissolves in both

28
Q

What do you observe when you add:
- dilute NH3
- Concentrated NH3

to AgBr?

A

Dilute NH3;
- does not dissolve

Conc:
- dissolves

29
Q

What do you observe when you add:
- dilute NH3
- Concentrated NH3

to AgI?

A

Dilute NH3:
Does not dissolve

Conc.
Does not dissolve

(Think of it as the halogens become less reactive as you go down the group).

30
Q

Why have we not mentioned flouride ions in the test for halides?

A

AgF is soluble in water. You cannot test for F- using silver nitrate.

31
Q

dfd

A

Chemistry (13 decks)

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