Group 7 - Topic 6

Question 1

Name of Group 7 elements:

Answer 1

halogens

Question 2

List all the Group 7 elements:

Answer 2

• fluorine
• chlorine
• bromine
• iodine
• astatine

Question 3

Symbol for fluorine:

Answer 3

F2

Question 4

Melting point and boiling point of fluorine:

Answer 4

• mp = -220 degrees C
• bp = -188 degrees C

Question 5

State of fluorine at RTP:

Answer 5

gas

Question 6

Colour of fluorine as a pure element:

Answer 6

pale yellow

Question 7

Colour of fluorine in water:

Answer 7

colourless

Question 8

Colour of fluorine vapour:

Answer 8

pale yellow

Question 9

Symbol for chlorine:

Answer 9

Cl2

Question 10

Melting point and boiling point of chlorine:

Answer 10

• mp = -101 degrees C
• bp = -35 degrees C

Question 11

State of chlorine at RTP:

Answer 11

gas

Question 12

Colour of chlorine as a pure element:

Answer 12

pale green/yellow-green

Question 13

Colour of chlorine in water:

Answer 13

pale yellow

Question 14

Colour of chlorine vapour:

Answer 14

pale green

Question 15

Symbol for bromine:

Answer 15

Br2

Question 16

Melting point and boiling point of bromine:

Answer 16

• mp = -7 degrees C
• bp = 59 degrees C

Question 17

State of bromine at RTP:

Answer 17

liquid

Question 18

Colour of bromine as a pure element:

Answer 18

red-brown

Question 19

Colour of bromine in water:

Answer 19

yellow-orange

Question 20

Colour of bromine vapour:

Answer 20

orange

Question 21

Symbol for iodine:

Answer 21

I2

Question 22

Melting point and boiling point of iodine:

Answer 22

• mp = 114 degrees C
• bp = 184 degrees C

Question 23

State of iodine at RTP:

Answer 23

solid

Question 24

Colour of iodine as a pure element:

Answer 24

purple-black

Question 25

Colour of iodine in water:

Answer 25

orange/brown

Question 26

Colour of iodine vapour:

Answer 26

purple

Question 27

Symbol for astatine:

Answer 27

At2

Question 28

Melting point and boiling point for astatine:

Answer 28

• mp = 302 degrees C
• bp = 337 degrees C

Question 29

State of astatine at RTP:

Answer 29

solid

Question 30

Colour of astatine as a pure element:

Answer 30

black

Question 31

What do Group 7 elements have in common?

Answer 31

• elements in Group 7 form diatomic molecules
• covalent bonds between halogen atoms

Question 32

Physical properties of Group 7 elements:

Answer 32

• diatomic
• simple covalent
• mp and bp increase as you go down Group 7

Question 33

What are the patterns in physical properties of halogens?

Answer 33

• There is a trend in state from gas to liquid to solid down the group
• this is because the melting and boiling points increase as you go down the group
• from this, you can predict that any halogens above chlorine will be gases (their boiling points will be even lower), and any below iodine will be solids (their melting points will be even greater)

Question 34

Why do the melting points of halogens get higher as you go down the group?

Answer 34

• the bonds within the molecules get weaker due to the larger distance between the nucleas and the shared pair of electrons due to their being more shells but these bonds don’t break during melting
• the intermolecular forces gets stronger as you go down Group 1, so more energy is needed to overcome them and melt the halogen

Question 35

What is the test for chlorine?

Answer 35

• When damp litmus paper is put into where the chlorine gas is suspected to be the litmus paper is bleached and turns white as chlorine is a bleaching agent
• litmus paper has to be damp so the water can react with the chloride - if it isn’t damp it will set on fire

Question 36

Why does the test for chlorine work (use this equation: Cl2(g) + H2O(l) —> HCl (aq) + HOCl (aq))

Answer 36

1. Some Cl reacts with water (on damp litmus paper) to form acids HCl and HOCl products change litmus paper to red (acid turns paper red)
2. Some chlorine gas (Cl2) is dissolved which bleaches the litmus paper and turns it white as chlorine is a bleaching agent

Question 37

Halide:

Answer 37

compound formed when halogens react with metals and non-metals

Question 38

What do halogens form when they react with metals and what is this type of reaction called?

Answer 38

• Compounds called halides
• They react with metals to form ionic compounds in which the halide ion carries a -1 charge. e.g. NaCl or MgBr2(as Mg has a +2 charge so you need two Br- to cancel this out)
• Direct combination reaction as 2 elements combine to form a compound e.g. aluminium + chlorine ——> Aluminium chloride

Question 39

What do halogen react with non-metals to form?

Answer 39

• compounds called halides
• bonding between these elements is covalent

Question 40

How do halogens react with water?

Answer 40

• halogen + hydrogen → hydrogen halide (HCl, HBr, HI)
• reaction becomes less vigorous down group: chlorine reacts in sunlight, but bromine will react in a flame (higher temperature)
• hydrogen halides dissolve in water to produce acidic solutions- in solution the hydrogen halide will fully dissociate into H+and halide-ions

Question 41

Halogens’ order of reactivity (least reactive to most reactive):

Answer 41

• Astatine (At) —> Iodine (I) —> Bromine (Br) —> Chlorine (Cl) —> Fluorine (F)

Question 42

What is the trend in reactivity of halogens and why?

Answer 42

• reactivity of halogens increases as you go up group 7
• halogens form negative ions when they react
• halogens need to gain an electron to gain a full outer shell when they react
• as you go down Group 7, there atoms become larger due to there being a greater number of shells
• so there larger distance/gap between the positive nucleus and the outer shell electrons due to increased electron shielding/the outer shell electron being further from the nucleus due to there being more shells
• therefore, there is a weaker force of nuclear attraction from the nucleus and incoming electrons/outer shell electrons to fill the outer shell so the halogen to gain a full outer shell
• so as you go down Group 7 the outer shell gains an electron less easily
• as you go down the Group 7, the reactivity of halogens decreases
• the halogens react by gaining an electron in their outer shell, as you go down the group:
  
  • outer shell becomes further from the nucleus
  • electron shielding causes attraction to decrease between nucleus and outer electrons
  • electrons are gained less easily
  • halogens become less reactive

Question 43

How does the trend of reactivity in Group 7 compare to the trend of reactivity in Group 1

Answer 43

• reactivity increases as you go down Group 1
• as negative outer shell electrons get further away from the nucleus so attraction between nucleus and outer shell electrons decreases allowing the metal atom to lose electrons and gain a full outer shell

Question 44

What can a more reactive halogen do in an aqueous solution of its salt?

Answer 44

• A more reactive halogen can displace a less reactive in an aqueous solution of its salt.
  
  • E.g. Chlorine will displace bromine if we bubble the gas through a solution of potassium bromide:
  • chlorine + potassium bromide —> potassium chloride + bromine

Question 45

What happens in displacement reactions involving halogens?

Answer 45

• More reactive halogen which displaces the less reactive one from the compound, forms a negative ion itself, therefore being reduced as it has gained electrons
• The less reactive halogen that is displaced is oxidised as it gains these electrons to go from a negative ion to an atom with 0 charge

Question 46

Key rules for ionic equations:

Answer 46

1. Covalent molecules don’t split up when they dissolve in water e.g. a Br2 (aq) molecule is the same as a Br2 (I) molecule
2. Soluble ionic compounds split up when they dissolve in water e.g. NaCl (s) —> NaCl (aq) is really Na+ (aq) + Cl- (aq)

Question 47

What does OILRIG stand for?

Answer 47

oxidation is loss, reduction is gain (of electrons)

Question 48

Why are these displacement reactions called redox reactions?

Answer 48

• because an element has been reduced and an element has been oxidised

Question 49

Explain the trend of relative reactivity of Group 7 elements in terms of electron configuration:

Answer 49

• halogen atoms gain an electron to obtain a full outer shell like a noble gas
• the nearer the outer shell is to the nucleus, the stronger the attraction for the incoming electron and so the more reactive the halogen is
• as you go down group 7 the size of the atoms becomes larger and the further the nucleus is from the outer shell
• this means that the attraction for the incoming electron and the nucleus becomes weaker and the halogens get less reactive towards the bottom of the group

Question 50

Halide ion:

Answer 50

• halides formed by hydrogen atoms when they gain an electron
• have a 1- charge

Question 51

Oxidation:

Answer 51

• a reaction involving the gain of oxygen
• the loss of electrons

Question 52

Reduction:

Answer 52

• reaction involving the loss of oxygen
• gain of electrons

Question 53

Redox reaction:

Answer 53

a chemical reaction in which oxidation nd reduction occur simultaneously

Question 54

Why are these displacement reactions (with group 7 elements) redox reactions?

Answer 54

• OILRIG
• more reactive halogen displaces less reactive one - forms a negative ion itself, therefore, being reduced as it has gained electrons
• less reactive halogen that is displaced is oxidised as it loses these electrons to go from a negative ion to an atom with 0 charge
• E.g. for the equation: chlorine + potassium bromide ——> potassium chloride + bromine
  
  • the symbol eqn without potassium is: Cl₂ + 2Br⁻ ——> 2Cl⁻ + Br₂
  • so for chorine the half equation is: Cl₂ + 2e⁻ ——> 2Cl⁻, chlorine has gained electrons so has been reduced
  • for bromine the half eqn is: 2Br⁻ ——> Br₂ + 2e⁻, bromine has lost electrons so it has been oxidised