Group 2 metals

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Physical properties

Electron arrangement

  • 2 electrons in outer shell
  • s-orbital becomes further away from nucleus going down group 2

Size of atoms

  • atomic radii increases due to the extra filled main level of electrons

Melting points

  • high melting points due to giant metallic structure
  • electrons in 'sea' are further away from positive nuclei going down group 2 so strength of metalli bonds decreases, causing melting points to decrease (starting with calcium)

Ionisation energies

  • all atoms in group 2 lose their two outer electrons
  • ions with +2 charge are formed
  • first and second ionisation energies decrease down group as atomic radii increases and shielding increases, resulting in electrons to be easier to leave the atom
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Chemical reactions with water

Metals get more reactive going down the group.

Where M is any group 2 metal:

M(s) + 2 H20(l) ---> M(OH)2(aq) + H2(g)

M(OH)2 is a hydroxide.

Magnesium hydroxide

  • called 'milk of magnesia'
  • used in indigestion remedies and neutralise excess stomach acid

Magnesium

  • reacts slowly with cold water (forming Mg(OH)2), but quickly with steam (forming MgO)

Calcium hydroxide

  • called 'slaked lime' - used to treat acidic soil
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Solubilities

Hydroxides

  • going down group, the hydroxides become more soluble
  • all are white solids

Magnesium hydroxide - almost insoluble

Calcium hydroxide - sparingly soluble (used as lime water)

Strontium hydroxide - more soluble

Barium hydroxide - dissolves to produce a strongly alkaline solution

Sulfates

  • going down group, the sulfates become less soluble

Barium sulfate - virtually insoluble so taken by mouth and used to outline the gut in medical x-rays

Testing for sulfate ions in solution ---> solution is acidified with nitric/hydrochloric acid (to remove carbonate ions as barium carbonate is also a white insoluble solid), then barium chloride is added. If a sulfate is present, a white precipitate of barium sulfate will be formed

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