Group 2, Alkaline Earth Metals

what ions do group 2 elements form

+2 ions

trend in atomic radius down group 2

increases, more shells

trend in 1st ionisation energy down group 2

decreases

why does 1st ionisation energy decrease down the group

• extra shells added as we go down

• = more shielding = weaker attraction between nucleus and outer electrons

• atomic radius increases = weaker attraction

• easier to remove the outer electron so less energy is needed

overrides increase nuclear charge

trend in melting point down group 2

decreases

describe the structure of group 2 elements

metallic structures, where you have positive metal ions attracted to a sea of delocalised electrons

why does melting point decrease down group 2

• size of metal ions increases, but number of delocalised electrons stays the same, 2+ charge stays the same too

• larger ions = larger distance between positive nuclei and delocalised electrons = weaker attractive force

• easier to break bonds

exception to the melting point trend in group 2?

magnesium, it decreases due to a structural difference compared to other group 2 metals

what do group 2 elements react with water to form

bases (metal hydroxides)

trend in reactivity down group 2 with water

reactivity increases down the group

why does reactivity increase with water down group 2

• atom gets larger and electron is further from nucleus

• easier to remove and hence more reactive

• more shielding

exception in group 2 reactions with water

magnesium, it reacts slowly with cold water

what does magnesium react more vigorously with, what does this produce

steam, producing magnesium oxide instead of a hydroxide

trend in solubility of group 2 metal surfaces down group 2

decreases down the group

as an anion has a double charge they become ? as we go down the group

less soluble

trend in solubility of group 2 hydroxides down group 2

increases going down group 2

if the anion has a single charge, what happens to solubility of hydroxides

more soluble

reagent used to test for sulfates

barium chloride

how to test for sulfates

• add HCL to remove carbonates

• add barium chloride

observation for a positive sulfates test

white precipitate, observed because barium sulfate formed is insoluble

why is it important to add hydrochloric acid before a sulfate test

to remove any carbonates which could precipitate out after adding barium chloride

how can group 2 elements be used

to neutralise acids:

• acidic soil neutralised

• antacids

also barium meal

ionic equation for neutralisation

H+ (aq) + OH- (aq) → H2O (l)

what can be used to neutralise acidic soils

calcium hydroxide, slaked lime

Ca(OH)2

what can be used as antacids

magnesium hydroxide, Mg(OH)2

neutralises excess stomach acid

what is barium meal and what is it used for

barium sulfate is used to help identify problems with the digestive tracts,

patient drinks barium sulfate then goes through an x-ray

why do we use barium sulfate as a barium meal

• dense, so can be picked up on an x-ray

• coats lining of soft tissue

• x-rays are absorbed by barium sulfate so soft tissues will show up on an x-ray

• insoluble so will not be absorbed into the blood

potential risk of barium sulfate

barium sulfate is toxic,

but it is insoluble so can’t be absorbed into the blood

what group 2 element is used to extract titanium from its ore

magnesium

step 1 of extraction of titanium

why do we heat titanium ore with carbon AND chlorine

need to heat with chlorine so carbon doesn’t react with titanium, which would form titanium carbide which is brittle

step 2 of extraction of titanium

titanium (IV) chloride produced in step 1 is passed through a fractional distillation column to increase the purity

step 3 of extraction of titanium

purified TiCl4 is reduced using magnesium in 1000°c furnace

reaction between titanium (IV) chloride with magnesium

titanium is reduced

magnesium is the reducing agent

uses of titanium

it is light weight but strong, and is commonly used in planes

what is used to remove sulfur dioxide emissions

calcium carbonate and oxide

importance of removing sulfur dioxide, how is it produced

burning fossil fuels for electricity produces the POLLUTANT. sulfur dioxide

what process is used to neutralise sulfur dioxide in flue gases

wet scrubbing

describe wet scrubbing process

involves dissolving calcium carbonate or oxide instead water and spraying it on acidic sulfur dioxide gas,

produces calcium sulfate which can be used for the production of plasterboard

use of calcium sulfite produced in wet scrubbing

production of plasterboard

wet scrubbing equations

CaCO3 (s) + 2H2O (l) + SO2 (g) → ?