Topic 6 - Groups in the Periodic Table✅

How can elements be classified as alkali metals, halogens, or noble gases

• Groups in the periodic table can be classified into specific groups e.g. Alkali metals, halogens, noble gases

• This is because they have the same number of electrons in their outer shell - therefore similar chemical properties

Name two properties of alkali metals

• Soft

• Low melting points

How does lithium react with water

• Fizzes steadily

• Creates lithium hydroxide and hydrogen

How does sodium react with water

• Melts into a ball then fizzes quickly

• Forms sodium hydroxide and hydrogen

How does potassium react with water

• Gives off sparks

• Burns with a lilac flame

• Forms potassium hydroxide and hydrogen

Describe the pattern in reactivity of the alkali metals

• Reactivity increases as you go down the group

• With water, the reactions get more vigorous as you go down the group

Explain this pattern of reactivity in terms of electronic configurations (gp1)

• Reactivity increases as you go down group 1

• All group 1 metals lose 1 electron when they react to obtain a full outer shell

• It is easier to lose electrons due to the increase in electron shells as you go down the group

• This means there is more electron shielding, and a decrease in the attraction between the nucleus and the outer shell electron

Why should alkali metals be stored in oil

To prevent them from reacting with water vapour and oxygen in the air

What is chlorine like at room temperature

Yellow-green gas

What is bromine like at room temperature

Red-brown liquid

What is iodine like at room temperature

Purple-black solid

Describe the pattern in the physical properties of chlorine, bromine and iodine

• There is a trend in state (from gas -> liquid -> solid) as you go down the group

• This is because melting / boiling point increases as you go down the group

How can you use this pattern to predict the state of other group 7 elements

• Anything above chlorine will be gas

• Anything below iodine will be solid

Why does melting / boiling point increase as you go down group 7

• Molecules get bigger down the group

• So there are more intermolecular forces to overcome during melting / boiling

• So more energy is required

What is the test for chlorine

• Put damp blue litmus paper into chlorine gas

• If it is chlorine then the litmus paper will bleach, turning red then white

What chemical properties do halides have

• All diatomic

• All have -1 charge

What is produced when a halogen reacts with a metal

• Metal halide

• E.g. Magnesium + fluorine = magnesium fluoride

Explain the relative reactivity of halogens in terms of electronic configuration

• Fluorine's elec config is 2.7

• Chlorine's elec config is 2.8.7

• This shows an extra shell of electrons is gained as you move down group 7

• This leads to greater shielding and weaker attraction between the nucleus and the outer shell electron, leading to reduced reactivity

Rate of reaction down group 7

• Decreases as you go down the group

• Because reactivity decreases as you go down the group

When does halogen displacement occur

• When a more reactive (higher up on the p. table) displaces a less reactive halogen

• From an aqueous solution

What colours are chlorine, bromine, iodine solutions

• Chlorine = colourless

• Bromine = orange

• Iodine = brown

What is a redox reaction

A reaction where oxidation and reduction occur simultaneously

Explain how halogen displacement reactions are redox reactions

• The halide ion is oxidised, to form a halogen atom

• The halogen is reduced to form a halide ion

Half equations for chlorine + potassium bromide

• Chlorine + potassium bromide -> bromine + potassium chloride

• Reduction = Cl₂ + 2e^- -> 2Cl^-

• Oxidation = 2Br^- -> Br₂ + 2e^-

Explain why noble gases are inert

• Noble gases have 8 electrons in their outer shell

• This means they have a full outer shell, making them unreactive as they don't need to lose or gain any electrons

Use of helium and why

• Helium is used in balloons and airships because it has a low density

• It is less dense than air, hence why balloons float upwards

Use of argon, krypton and neon and why

• Argon, krypton and neon are used in light bulbs because they are inert and non-flammable, stopping the filament from burning away

Trend in physical properties of noble gases

• Boiling points increase as you go down the group

• Densities increase as you go down the group