Group 2 - The Alkaline Earth Metals

A set of vocabulary flashcards detailing the physical properties, chemical reactions, and industrial/medical applications of Group 2 elements.

Alkaline earth metals

The name given to elements in Group 2 of the periodic table because their oxides and hydroxides are alkaline.

Atomic radius trend (Group 2)

The atomic (metallic) radii increase going down the group from $Mg$ to $Ba$ because each element has an extra filled main level of electrons compared with the one above it.

Melting point trend (Group 2)

Melting points generally decrease slightly going down the group starting with calcium, as the distance between the positive nuclei and the 'sea' of delocalised electrons increases, weakening the metallic bonds.

Magnesium (Melting Point)

The Group 2 element with the lowest melting point ($922\,K$), which represents an anomaly in the general group trend.

Ionisation energy trend (Group 2)

Both the first and second ionisation energies decrease going down the group as the outer electrons become further from the positive nucleus and are more effectively shielded by inner shells.

Group 2 General Ionisation Equation

$M(g) \rightarrow M^{2+}(g) + 2e^{-}$ represents the complete ionisation of a Group 2 metal atom.

Reactivity trend (Group 2)

The metals become more reactive going down the group from magnesium to barium.

Quicklime

Calcium oxide ($CaO$), produced by the thermal decomposition of limestone ($CaCO_3$) in lime kilns.

Slaked lime

Calcium hydroxide ($Ca(OH)_2$), used to neutralise and treat acidic soil to help crops like wheat, corn, oats, and barley thrive.

Milk of magnesia

A suspension of magnesium hydroxide ($Mg(OH)_2$) in water used in indigestion remedies to neutralise excess stomach acid.

Magnesium reaction with steam

Magnesium reacts rapidly with steam to form an alkaline oxide and hydrogen: $Mg(s) + H_2O(g) \rightarrow MgO(s) + H_2(g)$.

Titanium reduction equation

The reaction used to extract titanium from titanium chloride using magnesium: $TiCl_4(l) + 2Mg(s) \rightarrow 2MgCl_2(s) + Ti(s)$.

Hydroxide solubility trend (Group 2)

Solubility increases going down the group, ranging from the almost insoluble $Mg(OH)_2$ to the strongly alkaline solution produced by $Ba(OH)_2$.

Sulfate solubility trend (Group 2)

Solubility decreases going down the group, such that barium sulfate ($BaSO_4$) is virtually insoluble.

Barium meal

Virtually insoluble barium sulfate ($BaSO_4$) taken by mouth to outline the gut in medical X-rays; it is safe to use despite the toxicity of barium because of its extreme insolubility.

Test for sulfate ions

Acidify the test solution with nitric or hydrochloric acid and add barium chloride solution; a white precipitate of barium sulfate ($BaSO_4$) indicates a positive result.