Topic 1 · pp. 120–121 · Free
Topic Notes · Easy summaries with diagrams
Chapter 9 — Chapter 9 — Group Properties and Elements
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📘Easy summary
Alkali metals have ns¹ configuration; the single electron is lost easily (hydrogen is an exception, a non-metal gas). Down the group atomic size increases, so reactivity increases: Li reacts steadily, Na vigorously, K violently with water (2M + 2H₂O → 2MOH + H₂); reactions with chlorine also become more vigorous. Weaker interatomic attraction makes them softer with lower melting points (Li 180, Na 98, K 64, Rb 39, Cs 28 °C). Mass increases more than volume, so density increases (Li 0.53 … Cs 1.87 g/cm³).
⭐Key points
- Li, Na, K float on water; Rb sinks; Cs explodes in water.
- 2Na + Cl₂ → 2NaCl (heat).
🔬Diagram
🌿Real-life example
Potassium reacts violently with water, igniting the H₂.
💡Exam tip
- Learn Table 9.1 trend directions, not just values.
✅Quick check
1. Melting point down group 1:
2. Which sinks in water?
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