Topic 6- groups in the periodic table

Question 1

Why are elements classified in specific groups

Answer 1

• arranged in groups as alkalis, halogens and noble gases
• have the same number of electrons in their outer shell,
  so they have the same chemical properties

Question 2

describe the properties of alkali metals

Answer 2

• they’re soft

- have relatively low melting points

Question 3

describe reactions of lithium, sodium and potassium w/ water

Answer 3

• react vigorously w/ water to create an alkaline metal hydroxide and hydrogen.
• the reactions w/ water become more vigourous down the group, so reactivity of all alkali metals increases down the group

Question 4

Describe the reactivity of alkali metals in terms of electronic configurations

Answer 4

• Down the group – easier to lose electrons and form positive metal ions ( cations)
• easier to lose electrons because the electron shells increase as you go down the group.
• so there’s more electron shielding and a decrease in
  attraction between the positively charged nucleus and the negatively charged outer shell electron, so it can be lost more easily

Question 5

Colour of chlorine, bromine and iodine at room temp.

Answer 5

• chlorine is yellow/green gas
• bromine is red/brown liquid
• iodine is a purple solid

Question 6

test for chlorine

Answer 6

• damp litmus paper is put into chlorine gas, the litmus paper is bleached and turns white

Question 7

Describe what happens when lithium, sodium and potassium react with water

Answer 7

lithium - fizzes steadily
sodium - melts into a ball then fizzes quickly
potassium - gives off spark and hydrogen burns with lilac flame

Question 8

Describe the physical properties of halogens (group 7)

Answer 8

• the melting and boiling points increase as you go down the group
• so 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 9

How do halogens react with metals

Answer 9

• They react w/ metals to form ionic compounds and 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)
• Reaction is less vigorous as you move down group 7, but they still all react to form metal halides

Question 10

describe the reaction between halogen + hydrogen

Answer 10

• halogen + hydrogen → hydrogen halide e.g. HCl and reaction becomes less vigorous down group
• hydrogen halides dissolve in water to produce acidic solutions- in solution the hydrogen halide will fully dissociate into H+ and halide- ions

Question 11

displacement reactions with halide ions in aqueous

solution (effect of a more reactive halogen)

Answer 11

A more reactive halogen can displace a less reactive halogen in an aqueous solution
e.g. Chlorine + Potassium Bromide → Potassium Chloride + Bromine

Question 12

Describe the reaction of Chlorine + Potassium Bromine

effect of a more reactive halogen

Answer 12

• chlorine will displace bromine

Question 13

Describe the relative reactivity of halogens (effect of a more reactive halogen)

Answer 13

• chlorine will displace bromine and iodine
• bromine will displace iodine but not chlorine
• iodine can displace neither chlorine or iodine
• because as you go down the group, the reactivity of halogens decreases.

Question 14

What happens when you go down the group of halogens (in terms of reactivity

Answer 14

• the reactivity of halogens decreases

- also The halogens react by gaining an electron in their outer shell, as you go down the group

Question 15

What happens when the halogens gain an electron in their outer shell, as you go down the group

Answer 15

• outer shell becomes further from the nucleus
  o electron shielding increases
  o attraction decreases between nucleus and outer electrons
  o electrons are gained less easily
  o halogens become less reactive

Question 16

Explain redox reactions (OIL RIG)

Answer 16

• oxidation is loss, reduction is gain (of electrons)
• More reactive halogen displaces the less reactive halogen
• more reactive halogen forms a negative ion, so it’s being reduced, since it has gained electrons
• The less reactive halogen that is displaced is oxidised because it gains electrons to go from a negative ion to an atom with no charge

Question 17

Example of a redox reaction

chlorine + potassium bromide

Answer 17

chlorine + potassium bromide → potassium chloride +
bromine
- for chlorine the half equation is: Cl2 + 2e- → 2Cl- chlorine has gained electrons, so it’s been reduced
○ for bromine the half equation is: 2Br- → Br2 + 2e-
bromine has lost electrons, so it’s been oxidised

Question 18

Explain reactivity of halogens ( electronic configuration)

Answer 18

• electronic configurations of the halogens:
  ○ e.g. fluorine: 2,7
  ● these show clearly the extra shell of electrons gained as you move down group 7, which lead to greater shielding and weaker attraction, leading to reduced
  reactivity

Question 19

Why do the noble gases not react

Answer 19

• they all have a full outer shell, so they’re unreactive, because they’re already very stable

Question 20

uses of noble gases

Answer 20

• balloons
• inside light bulbs
• a shield gas during welding

Question 21

why are noble gases used in balloons (helium)

Answer 21

• = Helium used in balloons since it is much less dense

than air, so balloons filled with it float upwards

Question 22

Why are noble gases used inside light bulbs

Answer 22

• Inertness & non-flammability

- argon, krypton and xenon inside light bulbs, stops the filament burning away

Question 23

Why are noble gases used as a shield gas during welding

Answer 23

• Inertness= argon used as a shield gas during welding, - it’is also denser than air which keeps it away from the metal

Question 24

describe boiling points and density of noble gases

Answer 24

boiling points of the noble gases increase with increasing relative atomic mass (going down the group).
● densities of the noble gases increase as you go down the group