Chapter 9 - Group 2, the alkaline earth metals

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chapter 9 - Group 2, the alkaline earth metals

electron arrangement - 2 e-s in an outer s-orbital

the s-orbital becomes further away from the nucleus going down the group due to inc. shielding and weaker nuclear pull

atom size - inc. as you go down bc an extra layer of electrons each time you go down

melting points - high melting points, typical of giant metallic

strength of metallic bonds dec. as delocalised sea of electrons gets further away from the positive nuclei, the bonds become easier to break, so melting requires less energy: melting points dec. MAGNESIUM DOES NOT FIT THE TREND

ionisation energies - (losing two outer electrons for group 2) dec. down the group because it takes less energy to remove the electrons as they become further and further away from the positive nucleus and they are more shielded by more inner shells of electrons

the chemical reactions

they are all oxidised during reactions (oxidation state 0 to 2), meaning they are reducing agents of the other reactant

metals get MORE reactive as you go down the group bc the atomic radius inc. and the amount of shielding inc. so the nucleus has a weaker pull on outer electrons and can therefore lose them more easily, making them more reactive

milk of magnesia - used to help indigestion by neutralising excess stomach acid Mg(OH)2

the solubilities of the hydroxides and sulfates

hydroxides - inc. in solubility

all hydroxides are white solids

Mg(OH)2 - milk of magnesia almost insoluable, more of a suspension in water

Ca(OH)2 - sparingly soluable and the sol. is used as lime water

Sr(OH)2 - more soluable

Ba(OH)2 - dissolves to produce a strong alkali sol.

sulfates - dec. in solubility

BaSO4 is virtually insol. - taken by mouth to outline gut in X-rays bc it is insol. it can't damage the body (it is highly toxic)

can also be used as a test for sulfate ions

1.add an acid to remove carbonate ions as CO2 and stop the chance of side reactions happening

2. add BaCl and if sulfate ions are present, they will react w/ Ba to produce BaSo4 which will form a white ppt

nb: sulphuric acid must not be used as the acid bc that will add sulfate ions and will defeat the point of the test