Chemistry - Groups 1 & 2

Trend in melting point down each group?

Decreases down each group.

Metallic bonding gets weaker, due to the increased size and lower charge density of the metal cation but same number of electrons contributed to the delocalised electron cloud from each atom.

Meaning there is a weaker force of electrostatic attraction between the metal cations and the delocalised electrons, and so less energy is required to overcome these forces, and so the melting point is lower.

Why are melting points of group 2 metals higher than group 1 metals

Metallic bonding is stronger in group 2, since the metal cation has a charge of 2+ and so a higher charge density, and each atom contributes 2 electrons to the delocalised electron cloud rather than 1.

Meaning there is a strong force of electrostatic attraction between the metal cations and the delocalised electrons, and so more energy is required to overcome these forces, and so the melting point is higher.

Why do melting points tend to not give a decent trend?

Crystalline structure affects melting points.

Trend in ionisation energies down the group?

Decrease down the group.

Atomic size increases, greater distance from outer electron and nucleus.

Electron shielding increases, more shells between outer electron and nucleus,

Weaker forces of electrostatic attraction between outer electron and nucleus.

Less energy required to remove it, lower Ionisation energy

Despite increase in nuclear charge

Trend in reactivity down the group?

Increases down the group.

Due to the ease of cation formation,

Due to lower ionisation energies.

Trend in reaction with oxygen down group 2?

Notable observations of reaction with oxygen?

Reacts with increasing vigour down the group.

Mg burns readily with a bright white flame.

Ba burns readily with an apple-green flame

Trend in reaction with water down group 2?

Reacts with increasing vigour down the group.

M (s) + 2H₂O (l) —> M(OH)₂ (aq) + H₂ (g)

Beryllium doesn’t react with water

Magnesium reacts very slowly with cold water, but reacts quickly with steam.

Mg (s) + H₂O (g) —> MgO (s) + H₂ (g)

What type of reaction is metal + acid

Redox (not neutralisation, no proton transfer)

Are group 2 metal oxides covalent or ionic?

Ionic, but BeO has high covalent character

Trend with reactivity with water of Group 2 oxides down the group?

React with increasing vigour.

BeO does not react with water.

Trend of reactivity with acid of Group 2 oxides down the group?

React with increasing vigour.

BeO does not react with acid.

General equation of group 2 metal + acid?

General equation of group 2 metal oxide + acid?

General equation of group 2 metal hydroxide + acid?

M (s) + 2HA (aq) —> MgΑ₂ (aq) + H₂ (g)

MO (s) + 2HA (aq) —> MgΑ₂ (aq) + H₂O (l)

M(OH)₂ (s) + 2HA (aq) —> MgΑ₂ (aq) + 2H₂O (l)

Trend in solubility of hydroxides down group 2?

Increases down the group. (Don’t need to know why)

Be(OH)₂ is insoluble

Mg(OH)₂ is sparingly soluble

Ca(OH)₂ is slightly soluble

Trend in pH of hydroxides down group 2?

Alkalinity increases, pH increases down the group.

Because solubility of hydroxide increases,

meaning a greater concentration of OH- ions in solution.

Uses of Ca(OH)₂?

Uses of Mg(OH)₂?

Lime water, used to neutralise acidic soil.

Used in digestion tablets as an antacid.

Trend in solubility of group 2 metal sulfates down the group?

Decreases down the group.

BeSO₄ is soluble

MgSO₄ is soluble

CaSO₄ is slightly soluble

Explain the trend in solubility of the group 2 metal sulfates down the group

Solubility decreases down the group.

As the cation gets larger, charge density decreases.

Meaning its less attracted to polar water molecules.

Meaning the ionic lattice breaks up less easily.

Meaning it is less soluble.

Uses of BaSO₄?

Used for gastrointestinal X-rays.

Trend in thermal stability of G1/G2 nitrates and carbonates?

Increases down the group.

Metal ions with higher charge density, are more polarising.

This puts more strain on C-O or N-O bond in carbonate or nitrate ion.

Weakening the bond making it easier for the ion to decompose.

Maning it is less thermally stable

Decomposition of metal nitrates?

Group 1 except LiNO₃: Metal nitrate —> Metal nitrite + O₂

Group 2 and LiNO₃: Metal Oxide + NO₂ + O₂

NO₂ is a brown gas

Decomposition of metal carbonates?

Group 1 except Li₂CO₃: Do not decompose

Group 2 and Li₂CO₃: Metal carbonate —> Metal oxide + CO₂