Group 1 and 2: The Alkaline earth metals

Element Atomic AR EC MP/C Atomic radius Ionic radius 1IE 2IE Electronegativity
Be 4 9 [He]2s2 Increases Increases Increases Decreases Decreases Decreases
Mg 12 24 [Ne]3s2 Increases Increases Increases Decreases Decreases Decreases
Ca 20 40 [Ar]4s2 Increases Increases Increases Decreases Decreases Decreases
Sr 38 87.6 [Kr]5s2 Increases Increases Increases Decreases Decreases Decreases
Ba 56 137 [Xe]6s2 Increases Increases Increases Decreases Decreases Decreases

Group 1 vs Group 2: $Na$ vs $Mg$

Property Which is higher Why
Melting point Higher in group 2 2 electrons per ion in metallic bonding resulting in stronger materials; higher electrostatic force on delocalised electrons
Atomic radius Higher in group 1 Group 2 has more protons
Ionic radius Group 1 Group 2 has more protons
1IE Higher in group 2 Have to break full stability in 2, gaining stability in 1
2IE Higher in group 1 Breaking full stability in 1, gaining in 2
electronegativity Higher in group 2 When ionic, higher charge density in nucleus

Flame tests

Metal Ion Flame colour
Lithium Crimson red
Sodium Yellow
Potassium Lilac
Calcium Brick red
Strontium Red
Barium Apple green

When burned, the electrons in the outer S orbital jump to higher orbitals. This isn’t stable, on return they release a colour spectrum of energy, which is different for each.

Thermal stability and solubility

  • Anhydrous $CaCO_3$ - nothing happens
  • $LiCO_3$ – instant bubbles, doesn’t turn limewater cloudy for long time
  • $KCO_3$ – instant bubbles, but lower amount
  • $BaCO_2$ precipitate forms slowly at excess
  • $MgOH_2$ – turns cloudy in excess

Reactions

With oxygen
$2Mg+O_2\rightarrow2MgO$
With Chlorine:
$Mg+{Cl}_2\rightarrow\ {MgCl}_2$
With Water:
$Mg$ (cold water) $\rightarrow$ Hydroxide + $H_2$ - Suspended precipitate
$Mg$ (steam) $\rightarrow$ Oxide + $H_2$ - Precipitate
$Ca$ (cold) $\rightarrow$ Cloudy
Element Temperature Reaction with water
Be Hot
Mg Hot Mg\left(s\right)+2H_2O\rightarrow Mg(OH)_2+H_2
Ca Cold {Ca}_{(s)}+2H_2O\rightarrow Ca(OH)_2+H_2
Sr Cold {Sr}_{(s)}+2H_2O\rightarrow Sr(OH)_2+H_2
Ba Cold {Ba}_{(s)}+2H_2O\rightarrow Ba(OH)_2+H_2
Metal Oxide Acid Forms Equation
$BeO$ (amphoteric) Reacts with both acids & bases Salt + water $BeO+H^+\rightarrow B{e^{2+}}_{(aq)}+H_2O$
$BeO+{OH}^-\rightarrow B{e^{2+}}_{(aq)}+H_2O$
$MgO$ Acid Salt + water ${MgO}_{(s)}+2HCl_{(aq)}\rightarrow Mg{Cl}_{2(aq)}+H_2O_{(l)}$
${MgO}_{(s)}+2HNO_{3(aq)}\rightarrow Mg(NO_3)_{2(aq)}+H_2O_{(l)}$
${MgO}_{(s)}+H_2{SO}_{4(aq)}\rightarrow Mg{SO}_{4(aq)}+H_2O_{(l)}$
$CaO$ Acid Salt + water ${CaO}_{(s)}+2HCl_{(aq)}\rightarrow Ca{Cl}_{2(aq)}+H_2O_{(l)}$
${CaO}_{(s)}+2HNO_{3(aq)}\rightarrow Ca(NO_3)_{2(aq)}+H_2O_{(l)}$
${CaO}_{(s)}+H_2{SO}_{4(aq)}\rightarrow Ca{SO}_{4(aq)}+H_2O_{(l)}$
$SrO$ Acid Salt + water ${SrO}_{(s)}+2HCl_{(aq)}\rightarrow Sr{Cl}_{2(aq)}+H_2O_{(l)}$
${SrO}_{(s)}+2HNO_{3(aq)}\rightarrow Sr(NO_3)_{2(aq)}+H_2O_{(l)}$
${SrO}_{(s)}+H_2{SO}_{4(aq)}\rightarrow Sr{SO}_{4(aq)}+H_2O_{(l)}$
$BaO$ Acid Salt + water ${BaO}_{(s)}+2HCl_{(aq)}\rightarrow Ba{Cl}_{2(aq)}+H_2O_{(l)}$
${BaO}_{(s)}+2HNO_{3(aq)}\rightarrow Ba(NO_3)_{2(aq)}+H_2O_{(l)}$
${BaO}_{(s)}+H_2{SO}_{4(aq)}\rightarrow Ba{SO}_{4(aq)}+H_2O_{(l)}$
Limewater Carbon Dioxide Salt + water $Ca(OH)_{2\left(aq\right)}+CO_{2\left(g\right)}\rightarrow CaCO_{3\left(s\right)}+H_2O_{(l)}$

Solublity

Solubility of hydroxides increase down the group

Be Mg Ca Sr Ba
Insoluble Very slightly soluble Slightly soluble soluble Very soluble

Solubility of sulfates decreases down the group

Be Mg Ca Sr Ba
Soluble when hydrated Very soluble Slightly soluble Very slightly soluble Insoluble

Thermal stability

  • Thermal stability of ionic compounds depends on polarising power of the cations involved.
  • Polarisability depends on charge density, higher charge density, higher polarising power.
  • If polarising power of the cation is higher than the anion in the compound will decompose more easily
  • Lithium carbonate will decompose easily

Ions in order of polarising power, highest to lowest:

  1. $Mg^{2+}$
  2. $Na^+$ $Ca^{2+}$
  3. $K^+$
  4. $Ba^{2+}$
Nitrates Carbonates
Li 4LiNO_3+2Li_2O+3NO_2+O_2 Li_2CO_3\rightarrow Li_2O+CO_2
Na 2NaNO_3\rightarrow2NaNO_2+O_2 {Na}_2CO_3\rightarrow{Na}_2O+CO_2
G1 Ease of decomposition decreases down the group
Mg Mg({NO}_3)_2\rightarrow2MgO+4NO_2+O_2 MgCO_3\rightarrow MgO+CO_2
Sr Sr({NO}_3)_2\rightarrow2SrO+4NO_2+O_2 SrCO_3\rightarrow SrO+CO_2
G2 Ease of decomposition decreases down the group