10.3 - Physical and Chemical Properties of Halogens

Question 1

What are group 7 elements known as?

Answer 1

the halogens

Question 2

Uses of chlorine

Answer 2

water purification
bleaching agents

Question 3

Uses of bromine

Answer 3

flame-retardants
fire extinguishers

Question 4

Uses of iodine

Answer 4

antiseptics
disinfectant agents

Question 5

Colours of the halide gases

Answer 5

Question 6

what is volatility?

Answer 6

how easily a substance can evaporate
* a volatile substance will have a low b.p

Question 7

what happens going down group 7?

Answer 7

• the m.p and b.p of the group 7 elements increase going down the group
• becomes less volatile

Question 8

what type of molecules are halogens and what bonds do they form and how is this done?

Answer 8

• diatomic molecules
• covalent bonds are formed
• orbitals overlap

Question 9

what happens within a covalent bond?

Answer 9

the bonding pair of electrons is attracted to the nuclei to either side and this attraction holds the moleucle together

Question 10

what happens to the atomic size of the halogens?

what happens to the bonding pair of electrons and why?

Answer 10

• increases
• and the bonding pair of electrons get further away from the halogen nucleus and are therefore less strongly attracted towards it

Question 11

Whay happens to the bond enthalpy down the group?

Answer 11

the bond strength decreases due to the bond enthalpy decreasing

Question 12

What is bond enthalpy?

Answer 12

the energy needed to break one mole of covalent bonds

Question 13

Why is fluorine an exception in bond enthalpy?

Answer 13

• fluorine is so small that the lone pairs cause significant repulsion when close together
• counteracts the attraction between the bonding pair of electrons and two nuclei
  therefore is lower in bond enthalpy

Question 14

what structures are halogens and what IMF forces do they contain?

Answer 14

• simple molecular structures
• contains weak VDW forces between the diatomic molecules through instantaneous dipole dipole forces

Question 15

why does the m.p and b.p increase down the group?

Answer 15

• more electrons - more VDW forces
• larger the molecule the stronger the VDW forces
  more difficult to separate the molecule therefore volatility decreases

Question 16

Halogens as oxidising agents

Answer 16

• halogens can react with metals by accepting an electron from the metal atom to become an atom with a 1- charge
• halogens oxidise the metal and remove an electron and the halogens themselves are reduced

Question 17

What happens to the oxidising power of the halogens going down the group

Answer 17

decreases going down the group

Question 18

Electronegativity of halogens going down the group

Answer 18

• the atomic radii of the elements increase which means the outer shells get further away from the nucleus
• incoming electron will experience more shielding from the attraction of the positive nuclear charge
  ability to accept an electron therefore decreases

Question 19

how is the reactivity of halogens shown?

Answer 19

displacement reactions with other halide ions in solutions
* more reactive halogen displaces a less reactive halogen from a halide solution

• Cl2(aq) + 2NaBr (aq) → 2NaCl (aq) + Br2(aq)
• Cl2(aq) + 2Br-(aq) → 2Cl-(aq) + Br2(aq)

Question 20

Halide ions as reducing agents

Answer 20

can act as reducing agents by donating electrons to another atom
they get oxidised and lose electrons

Question 21

what happens to the reducing power down the group?

Answer 21

increases going down the group

Question 22

why does the reducing power of halogens increase going down the group?

Answer 22

• halide ions become larger
• outer electrons get further away from the nucleus
• more shielding is experineced due to inner electrons
• held less tightly as a result
  so electrons are lost more easily going down the group