2.2 Group 2 Flashcards
Melting point of group 2 elements
High
- Giant mettalic lattice
- Strong electrostatic forces of attraction
- Lots of energy to break metalic bonds
Density of group 2 (relative to group 1)
Higher density
- Group 2 ions are smaller
- Pack closer together
Reactivity of group 2 elements
All reactive metals (similar reactions as they have the same number of electrons in their outer shell)
Appearance of group 2 compounds
White crystalline ionic solids
Trend in atomic radius down group 2
Increases
- Atoms become larger
- More shellls + shielding
- Nuclear attraction to outer electron is less
Trend in first ionisation energy down group 2
Decreases
- More main shells + shielding
- Weaker attraction between nucleus and electron being removed
Trend in melting point down group 2
Decreases
- Metallic ions get bigger
- Less attraction between ions and delocalised electrons
Trend in reactivity down group 2
Increases
- React by losing electrons
- More shells + shielding
- Less nuclear attraction to the 2 outer electrons
Use of Magnesium
Extracting Ti from TiCl₄
Two reactions used to extract titanium from titanium oxide
React titanium oxide with chlorine and carbon
Reduce titanium chloride with magnesium
What makes titanium chloride easy to purify?
It is a liquid (distillation can be used)
Why is titanium difficult to extract from ores?
Reduction with carbon cannot be used (forms TiC, a brittle titanium carbide)
Trend in solubility down group 2 hydroxides
Increases
Solubility of Magnesium hydroxide
Sparingly soluable
Solubility of Barium hydroxide
Fully soluable
Trend in pH down group 2 hydroxides
Increases
Why does pH change down group 2 hydroxides?
Differences in solubility changes the number of hydroxide ions released into a solution
pH of Magnesium hydroxide
Around 8
pH of Barium hydroxide
Around 13
Use of Magnesium hydroxide
As an antacid to neutralise excess stomach acid
Use of calcium hydroxide
In agriculture to neutralise acidic soil
Trend in solubility down group 2 sulfates
Decreases
Solubility of Magnesium sulfate
Fully soluable
Solubility of Barium sulfate
Insoluable
Solubility of Calcium sulfate
Sparingly soluable
Use of Barium sulfate
Used in medicine (Barium meal) as it absorbs x-rays allowing soft tissue to be seen.
Why is Barium sulfate used in medicine despite Barium ions being toxic?
It is insoluble so cannot be absorbed into the blood
Uses of calcium compounds
To remove sulfur dioxide from flue gas (flue gas desulfurizarion)
Reaction of Mg with water
- Cold water: Forms Mg(OH)₂(s) + H₂(g) in a very slow reaction
- With steam: Forms MgO(s) + H₂(g) and a bright white light
Reaction of Ca with water
- Forms Ca(OH)₂(s) + H₂(g)
- Calcium hydroxide is slightly soluble and gives an alkaline solution
- White solid is still seen
(cold water)
Reaction of Sr with water
- Forms Sr(OH)₂(aq) + H₂(g)
- Strontium hydroxide forms an alkaline solution
- Some white solid is still seen
(cold water)
Reaction of Ba with water
- Forms Ba(OH)₂(aq) + H₂(g)
- Barium hydroxide forms a strongly alkaline solution
- No white solid is seen
(cold water)
Trend in reactivity with water as you go down group 2
Increases
Equation for forming titanium(IV) chloride from titanium ore
TiO₂ + 2Cl₂ + 2C –> TiCl₄ + 2CO
Equation for reducing titanium(IV) chloride with magnesium
TiCl₄ + 2Mg –> 2MgCl₂ + Ti
Test for Mg²⁺(aq) ions
Add aqueous sodium hydroxide, a thick white precipitate will form as Mg(OH)₂ is sparingly soluble
Test for Ba²⁺(aq) ions
Add sulfuric acid or aqueous sodium sulfate, a thick white precipitate will form as BaSO₄ is insoluable
What can barium salts be used for?
Testing for SO₄²⁻ ions (will form precipitate of BaSO₄ if present)
What can magnesium salts be used for?
Testing for OH⁻ ions (will form precipitate of Mg(OH)₂ if present)
