Group 2 – The Alkaline Earth Metals Flashcards
(32 cards)
Identify the block of the periodic table that Group 2 elements belong to.
Group 2 elements are in the s-block of the periodic table.
How many outer electrons do Group 2 elements have and what ions do they form?
Each has 2 electrons in their outer shell. They form 2+ ions when reacting.
Describe the trend in atomic radius down Group 2.
• Atomic radius increases down the group.
• More electron shells are added.
State and explain the trend in first ionisation energy down Group 2.
• First ionisation energy decreases down the group.
• Due to increased electron shielding from inner shells.
• Greater atomic radius because outer electrons further from nucleus.
• Although nuclear charge increases, its effect is outweighed.
Use data to explain why calcium has a lower first ionisation energy than magnesium.
Mg: 738 kJ/mol
Ca: 590 kJ/mol
➝ Ca has more shielding and a larger radius as a result lower IE.
Describe the trend in melting points down Group 2 and explain it.
• Melting points generally decrease down the group.
• Same number of delocalised electrons (2) and charge (+2).
• But metal ions get larger therefore delocalised electrons are further from nuclei resulting to weaker metallic bonds.
• ❗ Exception: Magnesium has an anomalously low MP due to a change in crystal structure.
Explain why reactivity increases down Group 2.
• Lower ionisation energy makes it easier to lose electrons forming M²⁺ ions more readily.
Group 2 metals reactions with Water
Write the general equation for the reaction between a Group 2 metal and water.
M(s) + 2H₂O(l) → M(OH)₂(aq) + H₂(g)
What is the change in oxidation state for the metal in this reaction?
0 → +2
Describe the trend in reactivity with water down Group 2. Use data to support your answer.
Reactivity with water increases down the group:
Reactivity
Be-No reaction
Mg- very slow
Ca -Steady
Sr- Fairly quick
Ba-Rapid
Solubility of Compounds Hydroxides
State the trend in solubility of Group 2 hydroxides down the group. Give examples.
Solubility increases down the group:
• Mg(OH)₂ = sparingly soluble
• Ba(OH)₂ = very soluble
State the trend in solubility of Group 2 sulfates down the group. Give examples.
Solubility decreases down the group:
• MgSO₄ = soluble
• BaSO₄ = insoluble
Test for Sulfate Ions
Describe how to test for sulfate ions and the observation that confirms their presence.
• Add dilute HCl, then BaCl₂.
• White precipitate of BaSO₄ indicates sulfate ions.
Medical Use of Barium Sulfate
Explain why BaSO₄ is used in medicine and why it is safe.
• BaSO₄ is insoluble and opaque to X-rays.
• Used as a barium meal to image soft tissues in X-rays.
• Safe as a suspension, not a solution (Ba²⁺ ions are toxic).
Industrial & Practical Uses
Extraction of Titanium
Outline the three key steps in the extraction of titanium using magnesium.
- TiO₂ + C + Cl₂ → TiCl₄
- TiCl₄ purified by fractional distillation
- TiCl₄ + 2Mg → Ti + 2MgCl₂ (at ~1000 °C)
Removing SO₂ – Wet Scrubbing
Describe how Group 2 compounds are used to remove SO₂ from flue gases. Include balanced equations.
• React CaO or CaCO₃ with water → alkaline slurry
• Slurry reacts with SO₂ in flue gases → CaSO₃ (solid waste)
Equations:
CaO + 2H₂O + SO₂ → CaSO₃ + 2H₂O
CaCO₃ + 2H₂O + SO₂ → CaSO₃ + 2H₂O + CO₂
Other Uses of Group 2 Compounds
Name two Group 2 hydroxides and their everyday uses.
Ca(OH)₂ (slaked lime) is used to Neutralise acidic soils in agriculture
Mg(OH)₂ is Used in antacids to neutralise stomach acid
Explain why the atomic radius increases down Group 2.
• More electron shells are added causing increased electron shielding.
• Outer electrons are in higher energy levels, further from nucleus.
• Electrostatic attraction between nucleus and outer electrons decreases.
State and explain the trend in first ionisation energy down Group 2
• Decreases down the group.
• Despite increased nuclear charge, the effect is outweighed by:
• Increased atomic radius
• Increased electron shielding
• Result: Weaker attraction to outer electrons as a result easier to remove.
Describe the general trend in melting points of Group 2 elements and explain the reason for this trend.
• Generally decrease down the group.
• Due to:
• Larger ionic radius
• Delocalised electrons are further from nuclei → weaker metallic bonding
Explain the trend in reactivity of Group 2 metals
• Increases down the group.
• Caused by:
• Lower first ionisation energy
• Easier to lose 2 outer electrons → form M²⁺ ions
• Reactions with water and oxygen become more vigorous down the group.
Magnesium is an anomaly in this trend. Explain.
❗ Magnesium has anomalously low MP due to a different crystal structure.
State what type of ions Group 2 elements form and how they achieve stability. Use examples in your answer.
• Group 2 metals form 2⁺ ions by losing their 2 outer s electrons.
• This results in a noble gas electron configuration.
Eg Be- 1s² 2s² = Be²⁺
Mg- 1s² 2s² 2p⁶ 3s² = Mg²⁺
Write the general equation for the reaction of a Group 2 metal with oxygen and state the oxidation and reduction changes
• 2M(s) + O₂(g) → 2MO(s)
• Metal: Oxidised (0 → +2)
• Oxygen: Reduced (0 → –2)
