3.2.2 Group 2

Physical and Chemical properties

  • Group 2 elements are ‘s’ block elements

  • They react similarly to Group 1 elements but are less reactive

  • The chemistry of Beryllium is atypical to the rest and isn’t considered

Physical Properties

Electron Arrangements

  • Highest 2 electrons in ‘s’ sub shells

  • Need to lose 2 electrons to form an outer shell = +2 ions

Atomic Radius

  • Increase in size going down the group

  • Each element has an additional filled electron shell below than the one above it

Melting Point

  • Group 2 elements are metals and form metallic bonds and giant metallic structures which results in a higher melting point

  • Down the group the ions get bigger as the attraction between delocalised electrons and metal ions is weaker so the metallic bonds are weaker therefore down the group the melting point decreases going down the group

Ionisation Energies

  • All Group 2 elements (alkali metals) always lose 2 electrons to form a 2+ ion

  • This means enough energy is needed to cause the first and second ionisation of a group 2 metal

  • After the first ionisation the ionisation energy decreases as the outer most electrons are held further away so less energy is required to overcome the attraction between the nucleus and the outer 2 electrons

Chemical Reactions of Group 2 Elements

  • Oxidation is the loss of electrons

  • All Group 2 elements lose 2 electrons to achieve a full outer shell

  • All group 2 elements are always oxidised during reactions

Reactions with Water(liquid)

  • All Group 2 elements react with water at room temperature = (element) hydroxide and hydrogen gas

  • The reactivity of Group 2 elements increase going down the group so Mg is the least reactive and B is the most reactive = reactions become more violent as the group descends

The group 2 hydroxides are alkali so the the pH of the hydroxide solution is greater than 7

Mg(OH)2 is used as an indigestion remedy to neutralise stomach acid

Reactions with Steam

Mg reacts more vigorously with steam than cold water

Group 2 elements have similar reactions with steam but are also increasingly more vigorous as the group descends

Hydroxides

Mg(OH)2 = Sparingly soluble

Ca(OH)2 = Sparingly Soluble

Sr(OH)2 = More Soluble

Ba(OH)2 = Completely Dissolves

Sulfates

MgSO4 = Completely Dissolves

CaSO4 = Fairly Soluble

SrSO4 = Sparingly Soluble

BaSO4 = Insoluble

Uses of Barium Sulfate

  • Barium Sulfate is very good at absorbing X rays and cannot pass through soft tissues or internal organs

  • Barium Sulfate is highly toxic

  • Due to its insolubility it cannot dissolve and pass through cell membranes into body tissue

Uses of Group 2 Hydroxides

  • Mg(OH)2 = Indigestion Tablets - alkali so it neutralises stomach acid

  • BaSO4 = Toxic but insoluble so safe when ingested so used for x-rays

  • Ca(OH)2 = alkali so it can neutralise acidic soils in farming

Testing for Sulfate Ions

  • Barium sulfate is so insoluble it forms a white precipitate

  • Use Barium Chloride

  • No change = no sulfate ions present

  • If a WHITE PRECIPITATE forms it indicates that there are sulfate ions present in the solution

NEED TO KNOW:

Nitric Acid is added to the sample prior to the test to remove any other ions affecting the test

During the reaction

  • Ba2+(aq) + SO4²-(aq) → BaSO4(s)

Extraction of Titanium

  • Magnesium is used to extract titanium from its ore - titanium chloride

  • Magnesium is used to reduce Ti4+ to Ti