group 2 trends

name of group 2 metals

Alkaline earth metals

is Be typical of group 2?

no

describe the electron arrangement

• two electrons in outer s orbital

• s orbital becomes further away from nucleus going down

describe size of atoms + why

• atomic radius increases downwards, shielding increases, more inner shells, increase effective nuclear charge

compare ionic radius from atomic radius

ionic radius is always smaller

describe melting point + why

• melting point decreases down the group, electron in outer shell is further away from positive nucleus, the strenght of metallic bond decreases

which element has the lowest MP

magnesium so deviated from this trend

what happens to the first and second ionisation energy

decreases down group, it takes less energy to remove the electrons as they become further away from positive nucleus, as more shielding of electron shells

describe reactivity

increases down the group

all metals in group 2 get

oxidised and loose 2 electrons

role of magnesium hydroxide

indigestion tablet + neutralise stomach acid

role of calcium hydroxide

Neutralise acidic soil

What happens when Magnesium burns in oxygen

burns readily in a bright white flame

what happens when barium burns in oxygen

burns readily with an apple green flame

Magnesium and cold water

reacts slowly

Mg + 2H2O (l) → Mg(OH)2 (aq) + H2

Magnesium and steam

reacts rapidly with steam

Mg + H2O (g) → MgO(s) + H2

Barium reacts …. with cold water

rigorously

what happens to solubilities of hydroxides going down the group

more soluble (white solids)

magnesium hydroxide is

insoluble

calcium hydroxide is … + solution used as…

sparingly soluble + lime water

barium hydroxide is… + forms a …. solution

dissolves readily + strong alkaline solution

Why does basic strength (alkali) of hydroxides increase down group

solubility increases, metal ion gets larger so charge density decreases, lower attraction between oh- ions and larger +2 ions, ions split from each-other easily, greater concentration of oh- ions in water, pH increases

what happens to solubility of sulphates going down the group + why?

decreases + cation gets larger and lower charge density, less attracted to water molecules

charge density depends on

size of ion + charge of ion

barium sulphate can be used to

absorb x rays

what can the insolubility of barium sulphate be used for

simple test for sulphate ions

Describe test for sulphate ions

• first acidify solution with nitric acid

• Barium chloride is added

• white precipitate if barium sulphate formed

what does the addition of acid do?

removes carbonate ions by co2 formation, as barium carbonate is also a white insoluble solid