Group 2: properties, reactions of elements and compounds, trends

Group 2 Elements: An Overview

Exam Tip: Remember that Group 2 elements are called the alkaline earth metals. They are all shiny, soft metals that form +2 ions. In exam questions, look for the “+2” charge when predicting ionic compounds.

Physical Properties

🔬 Softness & Shine: Think of a silver coin – the metals in Group 2 are as soft as that coin. They’re shiny because they reflect light well. ⚡ Low Melting & Boiling Points: Compared to heavier metals, they melt and boil at relatively low temperatures, like a candle flame (≈ 300 °C for magnesium). 💡 Density: They’re denser than the lighter alkali metals but lighter than transition metals. 📚 Analogy: Imagine a stack of books: the heavier the book, the more it pushes down. Group 2 metals are “medium‑weight” books in the periodic table.

Chemical Properties

🧪 Reactivity: They react with water to give hydroxides and hydrogen gas, but the reaction gets faster down the group. ✏️ Oxidation States: Always +2 in compounds – they lose two electrons to achieve a noble‑gas configuration. 📚 Analogy: Picture a pair of socks (two electrons). When they slip off (lose electrons), the metal becomes a stable ion.

Common Reactions

  • Reaction with Water: $\,\text{Mg} + 2\,\text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2 + \text{H}_2 \uparrow$ Note: The reaction is slow for magnesium but rapid for barium.
  • Reaction with Oxygen: $\,2\,\text{Ca} + \text{O}_2 \rightarrow 2\,\text{CaO}$ Result: Calcium oxide (lime) – a white powder that feels gritty.
  • Reaction with Halogens: $\,\text{Ba} + \text{Cl}_2 \rightarrow \text{BaCl}_2$ Use: Barium chloride is a bright yellow solution used in fireworks.
  • Reaction with Acids: $\,\text{Ca(OH)}_2 + 2\,\text{HCl} \rightarrow \text{CaCl}_2 + 2\,\text{H}_2\text{O}$ Result: Calcium chloride dissolves in water to give a clear solution.

Trends Across the Periodic Table

Property Be Mg Ca Sr Ba
Atomic Radius 1.53 ? 1.30 ? 1.98 ? 2.49 ? 2.68 ?
First Ionisation Energy 9.32 eV 7.64 eV 6.11 eV 5.68 eV 5.21 eV
Electronegativity (Pauling) 1.57 1.31 1.00 0.95 0.89

Trend Summary: As you move down Group 2, the atomic radius increases (atoms get bigger), ionisation energy decreases (easier to remove an electron), and electronegativity decreases (less pull on electrons). This explains why barium reacts more vigorously with water than beryllium.

Exam Tips

✏️ Predicting Products: Always check the oxidation state of the metal (+2) and the typical anion it forms (OH⁻, O²⁻, halides). 📚 Reaction with Water: Write the balanced equation and note the gas produced (H₂). 🔍 Trend Questions: Use the table to justify why a lower ionisation energy leads to higher reactivity. 📖 Remember the Analogy: Think of the metal as a pair of socks – losing both socks (electrons) gives you a stable ion. This helps recall the +2 charge. 🎯 Time Management: Allocate 2–3 minutes for each reaction question; write the balanced equation first, then explain the trend or reasoning.

Revision

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