3.1.3 Group 7

Question 1

Describe the physical structure and bonding of the halogens

Answer 1

DIATOMIC MOLECULES
- simple molecular lattice in the solid state
- with induced dipole-dipole interactions

Question 2

What are the colours and states of the halogens at RTP?

Answer 2

fluorine = yellow gas
chlorine = green gas
bromine = red/brown liquid
iodine = grey solid

Question 3

Describe the trend in boiling point of the halogens

Answer 3

Boiling points increase down the group
* molecules get larger
* so there are more electrons
* so there are stronger induced dipoles and more energy needed to overcome the induced dipoles

Question 4

Describe the outer shell electron configuration and ion formed in halogens

Answer 4

s^2 p^5 (7 electrons in the outer shell)
- they gain one electron to form a 1- ion

Question 5

Describe the trend in reactivity of the halogens

Answer 5

Reactivity decreases down the group
* atomic radius and shielding increase
* so attraction between the nucleus and outer electron** decrease**
* halogens become** LESS OXIDISING**

Question 6

How does the reaction between halogens and halide ions show reactivity ?

Answer 6

• Halogens will DISPLACE less reactive halide ions from a solution
• causing a colour change to occur

Question 7

What us added in the halogen-halide reactivity reaction to make the colour changes more defined?

Answer 7

• organic solvent is added
• shake
• halogen will dissolve in the solvent to form a distinct layer on TOP

Question 8

What colour is Cl2 in water and in hexane?

Answer 8

water = pale green
hexane = colourless

Question 9

What colour is Br2 in water and in hexane?

Answer 9

water = orange
hexane = dark red/brown

Question 10

What colour is iodine in water and hexane?

Answer 10

water = brown
hexane = purple

Question 11

Why is chlorine more reactive than bromine and iodine ?

Answer 11

• smaller atom so less shielding
• strong attraction between outer electrons and the nucleus

Question 12

Define disproportionation

Answer 12

simultaneous oxidation and reduction of the same element

Question 13

What is produced in a reaction of chlorine and cold, dilute sodium hydroxide?

Answer 13

sodium chloride (NaCl) , sodium chlorate (I) (NaClO) and water

sodium chlorate = household bleach

Question 14

What is produced in a reaction of chlorine and water?

Answer 14

chloric (I) acid (HClO) and hydrochloric acid (HCl)

Question 15

How can the disproportionation of chlorine in water be used in water purification ?

Answer 15

• aqueous chloric (I) acid ionises into chlorate (I) ions (ClO-)
• chlorate ions can kill bacteria

Question 16

Can you list and describe the benefits of chlorine use in water treatment contrasted with associated risks?

Answer 16

Benefits
* kills disease causing microorganisms
* prevents algal growth (no bad taste/smell)
Risks
* chlorine gas can irritate respiratory system
* chlorine can react with organic compouns to form CHLORINATED HYDROCARBONS which are carcinogenic

Risk of chlorinated hydrocarbons is small compared to health risk of untreated water