group 17

Question 1

Colour and state of fluorine in room temp

Answer 1

Pale yellow gas

Question 2

What are the Group 17 elements called?

Answer 2

The Group 17 elements are called halogens.

Question 3

What is one use of chlorine?

Answer 3

Chlorine is used in water purification as a bleaching agent.

Question 4

What is one use of bromine?

Answer 4

Bromine is used as a flame-retardant and in fire extinguishers.

Question 5

What is one use of iodine?

Answer 5

Iodine is used as an antiseptic and disinfectant agent.

Question 6

Colour and state of chlorine in room temp

Answer 6

Green yellow gas

Question 7

Colour and state of bromine in room temp

Answer 7

Brown/orange liquid

Question 8

Colour and state of iodine in room temp

Answer 8

grey/black solid solid
purple vapour

Question 9

What does volatility refer to?

Answer 9

Volatility refers to how easily a substance can evaporate.

Question 10

What characteristics does a volatile substance have?

Answer 10

A volatile substance will have a low melting and boiling point.

Question 11

What trend occurs in the melting and boiling points of Group 17 elements?

Answer 11

The melting and boiling points of the Group 17 elements increase going down the group.

Question 12

What does the increase in boiling point indicate about the volatility of halogens?

Answer 12

Going down the group, the boiling point of the elements increases, which means that the volatility of the halogens decreases.

Question 13

Which halogen is the most volatile?

Answer 13

Fluorine is the most volatile.

Question 14

Which halogen is the least volatile?

Answer 14

Iodine is the least volatile.

Question 15

How do halogens react with metals?

Answer 15

Halogens react with metals by accepting an electron from the metal atom to become an ion with 1- charge.

Example: Ca (s) + Cl2 (g) → Ca2+ (Cl-)2 (s)

Question 16

What role do halogens play in reactions with metals?

Answer 16

Halogens are oxidising agents.

Question 17

How do halogens oxidise metals?

Answer 17

Halogens oxidise the metal by removing an electron from the metal, increasing the oxidation number of the metal.

Question 18

What happens to halogens during the reaction with metals?

Answer 18

Halogens become reduced as they gain an extra electron from the metal atom, decreasing the oxidation number of the halogen.

Question 19

How does the oxidising power of halogens change down the group?

Answer 19

The oxidising power of the halogens decreases going down the group, meaning the halogens get less reactive.

Question 20

What does electronegativity refer to?

Answer 20

The electronegativity of an atom refers to how strongly it attracts electrons towards itself in a covalent bond.

Question 21

How is electronegativity related to the size of halogens?

Answer 21

The decrease in electronegativity is linked to the size of the halogens.

Question 22

What happens to atomic radii as you go down the group of halogens?

Answer 22

Going down the group, the atomic radii of the elements increase, meaning that the outer shells get further away from the nucleus.

Question 23

What effect does increased atomic radius have on incoming electrons?

Answer 23

An ‘incoming’ electron will experience more shielding from the attraction of the positive nuclear charge.

Question 24

What happens to the halogens’ oxidising power as you go down the group?

Answer 24

The halogens’ ability to accept an electron (their oxidising power) therefore decreases going down the group.

Question 25

What is thermal stability?

Answer 25

Thermal stability refers to how well a substance can resist breaking down when heated.

Question 26

What happens to a thermally stable substance at high temperatures?

Answer 26

A substance that is thermally stable will break down at high temperatures.

Question 27

How does thermal stability change among hydrogen halides?

Answer 27

The hydrogen halides formed from the reaction of halogen and hydrogen gas decrease in thermal stability going down the group.

Question 28

What explains the decrease in thermal stability of hydrogen halides?

Answer 28

The decrease in thermal stability can be explained by looking at the bond energies of the hydrogen-halogen bond.

Question 29

What happens to the atomic radius of halogens going down the group?

Answer 29

Going down the group, the atomic radius of the halogens increases.

Question 30

How does the atomic radius affect the bond length with hydrogen?

Answer 30

The overlap of its outer shell with a hydrogen atom therefore gives a longer bond length.

Question 31

What is the relationship between bond length and bond strength?

Answer 31

The longer the bond, the weaker it is, and the less energy required to break it.

Question 32

How does bond strength affect the stability of hydrogen halides?

Answer 32

As the bonds get weaker, the hydrogen halogens become less stable to heat going down the group.

Question 33

What do halogens react with to form hydrogen halides?

Answer 33

Halogens react with hydrogen gas to form hydrogen halides.

Question 34

How does the reactivity of halogens change down the group?

Answer 34

The reactivity of halogens decreases going down the group.

Question 35

What happens to the vigor of reactions between halogens and hydrogen gas as you go down the group?

Answer 35

The reactions become less vigorous.

Question 36

Observations of H2 (g) + F2 (g) → 2HF (g)

Answer 36

Reacts explosively, even in cool / dark conditions

Question 37

Observations of H2 (g) + Cl2 (g) → 2HCl (g)

Answer 37

Reacts explosively in sunlight

Question 38

Observations of H2 (g) + Br2 (g) → 2HBr (g)

Answer 38

Reacts slowly on heating

Question 39

Observations of H2 (g) + I2 (g) rightwards harpoon over leftwards harpoon 2HI (g)

Answer 39

Forms an equilibrium mixture on heating

Question 40

What is a disproportionation reaction?

Answer 40

A disproportionation reaction is a reaction in which the same species is both oxidised and reduced.

Question 41

Can you give an example of a disproportionation reaction?

Answer 41

The reaction of chlorine with dilute alkali is an example of a disproportionation reaction.

Question 42

What happens to chlorine in a disproportionation reaction?

Answer 42

In these reactions, the chlorine gets oxidised and reduced at the same time.

Question 43

Do different reactions occur at different temperatures of dilute alkali?

Answer 43

Yes, different reactions take place at different temperatures of the dilute alkali.

Question 44

What is the reaction of chlorine in cold alkali (15 oC)?

Answer 44

Cl2 (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)

Question 45

What is the ionic equation for the reaction of chlorine in cold alkali?

Answer 45

Cl2 (aq) + 2OH– (aq) → Cl– (aq) + ClO– (aq) + H2O (l)

Question 46

What does the ionic equation show about chlorine?

Answer 46

Chlorine undergoes disproportionation, i.e. gets both oxidised and reduced.

Question 47

How does chlorine get oxidised in the reaction?

Answer 47

There is an increase in oxidation number from 0 in Cl2 (aq) to +1 in ClO– (aq).

Question 48

What is the half-equation for the oxidation reaction of chlorine?

Answer 48

½Cl2 (aq) + 2OH– (aq) → ClO– (aq) + H2O (l) + e–

Question 49

How does chlorine get reduced in the reaction?

Answer 49

There is a decrease in oxidation number from 0 in Cl2 (aq) to –1 in Cl– (aq).

Question 50

What is the half-equation for the reduction reaction of chlorine?

Answer 50

½Cl2 (aq) + e– → Cl– (aq)

Question 51

What is the reaction of chlorine in hot alkali (70 oC)?

Answer 51

3Cl2 (aq) + 6NaOH (aq) → 5NaCl (aq) + NaClO3 (aq) + 3H2O (l)

Question 52

What is the ionic equation for the reaction of chlorine in hot alkali?

Answer 52

3Cl2 (aq) + 6OH– (aq) → 5Cl– (aq) + ClO3– (aq) + H2O (l)

Question 53

What type of reaction does chlorine undergo in this process?

Answer 53

Chlorine undergoes disproportionation, getting both oxidised and reduced.

Question 54

How does chlorine get oxidised in this reaction?

Answer 54

Chlorine's oxidation number increases from 0 in Cl2 (aq) to +5 in ClO3– (aq).

Question 55

What is the half-equation for the oxidation reaction of chlorine?

Answer 55

½Cl2 (aq) + 6OH– (aq) → ClO3– (aq) + 3H2O (l) + e–

Question 56

How does chlorine get reduced in this reaction?

Answer 56

Chlorine's oxidation number decreases from 0 in Cl2 (aq) to –1 in Cl– (aq).

Question 57

What is the simplified half-equation for the reduction reaction of chlorine?

Answer 57

½Cl2 (aq) + e– → Cl– (aq)