Group 2 Elements: Key Concepts

Atomic Radius

• Increases down the group due to additional electron shells.

Ionization Energy

• Decreases down the group.
• Outer electrons are more weakly held as they are farther from the nucleus and more shielded by inner electrons.

Melting Points

• Decrease down the group.
• Metallic bonding weakens as atomic size increases.
• Greater distance between positive ions and delocalized electrons weakens electrostatic forces.

Reactions and Reactivity

Reactivity

• Increases down the group.
• Magnesium reacts slowly with oxygen without a flame, often forming a magnesium oxide layer.

Reaction with Oxygen

• Group 2 metals burn in oxygen; magnesium burns with a bright white flame producing MgO.

Reaction with Water

• Magnesium reacts with steam to form MgO and H2.
• Other Group 2 metals react with cold water, forming hydroxides and H2, with increasing vigour down the group.
• Mg reacts with warm water to form Mg(OH)2 more slowly than with steam.

Using Magnesium to Extract Titanium

• Titanium's extraction is costly due to the need for pure titanium.
• Extracted by reacting TiCl4 with Mg in an argon atmosphere.
• Factors contributing to high cost: expensive magnesium, batch process, argon, and moisture removal.

Removing SO2 from Waste Gases

• Calcium oxide removes SO2 by forming calcium sulfite, which can be used to produce plasterboard.

Solubility of Compounds

Sulfates

• Group II sulfates become less soluble down the group.
• BaSO4 is the least soluble and used in medical X-rays due to low solubility.

Testing for Sulfate Ions

• Using BaCl2 in an acidified solution to form a white precipitate of BaSO4.
• Avoid sulfuric acid for testing due to existing sulfate ions.

Hydroxides

• Solubility increases down the group.
• Calcium hydroxide is partially soluble; forms white precipitate, used to neutralize acidic soils.
• Magnesium hydroxide is used as a weakly alkaline medicine.

Precipitation Reactions

Formation of Insoluble Salts

• Mixing solutions to form a precipitate.
• Example: Ba(NO3)2 + Na2SO4 → BaSO4 + NaNO3.

Filtration Techniques

• Gravitational Filtration: for small amounts.
• Vacuum Filtration: for larger amounts, uses Buchner flask and funnel.

Common Solubility Rules

• Sodium, potassium, ammonium salts, and nitrates are generally soluble.
• Silver, lead chlorides, bromides, iodides, and some sulfates are insoluble.