Halogens

Question 1

What are the characteristic physical properties of halogens? (5)

Answer 1

• halogens are the most reactive non - metals
• They do not occur in elemental form in nature
• At room temperature they exist as diatomic molecules
• They contain elements in all 3 physical states

Question 2

What is the trend in properties of halogens

Answer 2

As you go down the halogens, boiling point increases and density increases
Reactivity decreases

Question 3

Why does the boiling point increase down the halogen group?

Answer 3

• The number of electrons increases which increases the strength of London forces.
• This means more energy is required to break the intermolecular forces in the molecule which increases the boiling point

Question 4

What is the appearance and state at RTP of fluorine

Answer 4

• It is a pale yellow gas

Question 5

What is the appearance and state at RTP of chlorine?

Answer 5

Pale green gas

Question 6

What is the appearance and state of bromine at RTP?

Answer 6

Red - brown liquid

Question 7

What is the appearance and state of iodine at RTP?

Answer 7

It is a shiny grey black solid

Question 8

What are the redox reaction of halogens

Answer 8

• halogens have 7 outer electrons and redox reactions are their most common reaction
• Each halogen atom is reduced and gains one electron to have a full outer shell (-1 charge)
• Another species then gains the looses an electron to the group 7 ion, so halogens are oxidising agents

Question 9

How can we tell that reactivity decreases down a group?

Answer 9

Through displacement reactions

Question 10

Why does reactivity decrease down a group?

Answer 10

• Atomic radius increases which increases shielding
• more repulsion and less nuclear attraction between the nucleus and outer electron
• this reduces reactivity
• harder to gain an electron

Question 11

What is the most reactive element in group 7?

Answer 11

Fluorine

Question 12

What is Disproportionation reaction?

Answer 12

It is a redox reaction in which the same element is both oxidised and reduced

Question 13

What are common examples of disproportionation reactions

Answer 13

• The reaction of chlorine and water
• ## The reaction of chlorine and dilute NaOH

Question 14

What is the reaction of water and chlorine

Answer 14

Cl2 (aq)+ H20(L) - HCLO(aq) + HCL(AQ)

Question 15

What are the products of the reaction of water and chlorine used for?

Answer 15

• The products are chloric acid and hydrochloric acid
• Chloric acid acts as a weak bleach and chlorine can be used as a water disinfectant as it kills bacteria

Question 16

What is the reaction of chlorine with cold, dilute NaOH?

Answer 16

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

Question 17

What are the products used for?

Answer 17

The chlorate ions ClO- in NaClO are present in household bleach

Question 18

What are the benefits and risks of chlorine use?

Answer 18

• Useful in disinfecting water
• Kills harmful bacteria
• Without chlorine, water could contain harmful and infectious bacteria that can cause cholera and typhoid

Question 19

What are the risks of chlorine usage?

Answer 19

• It is an extremely toxic gas
• It is a respiratory irritant in small concentrations and fatal in large
• chlorinated water reacts with organic hydrocarbons which can cause chlorinated hydrocarbons which can cause cancer

Question 20

Do the benefits outweigh the risks?

Answer 20

yes, the overall risk of contaminated water is more dangerous and risky than chlorinated hydrocarbons