Key Concepts: Alkali metals (Group 1) react with water to form a metal hydroxide and hydrogen. Reactivity increases down the group because the outer electron is further from the nucleus and more shielded, so it is lost more easily.
Section A — Properties of Group 1
1. Name four alkali metals and state the group and period they are found in on the periodic table. [3]
2. Give three physical properties that alkali metals share. [3]
3. Complete the sentence: Alkali metals have _____ electron(s) in their outer shell and form _____ ions in chemical reactions. [2]
4. Explain why alkali metals are stored under oil. [2]
Section B — Reactions with Oxygen
5. Complete the word equation: alkali metal + oxygen → _________________ [1]
6. Write balanced symbol equations for the following reactions with oxygen. [3]
a) Lithium + oxygen
b) Sodium + oxygen
c) Potassium + oxygen
Section C — Reactions with Water
7. State two observations when sodium is placed in water. [2]
8. Write the general word equation for an alkali metal reacting with water. [1]
9. Balance the equations below for alkali metals reacting with water. Fill in the missing coefficients. [3]
a) ___Li + ___H₂O → ___LiOH + ___H₂
b) ___Na + ___H₂O → ___NaOH + ___H₂
c) ___K + ___H₂O → ___KOH + ___H₂
10. Name the gas produced in the reaction with water and describe how you would test for it. [2]
11. Explain how the similar reactions of lithium, sodium and potassium with water provide evidence that they are a family of elements. [2]
Section D — Reactivity Trend and Predictions
12. Put Li, Na and K in order of increasing reactivity. [1]
13. Explain why reactivity increases down Group 1. [3]
14. State two differences you would observe between the reactions of lithium and potassium with water. [2]
15. Predict how rubidium (Rb) would react with water compared to potassium. Give a reason for your prediction. Write a balanced symbol equation for the reaction. [3]
Total marks: 33
Mark Scheme
1. Any four from: lithium, sodium, potassium, rubidium, caesium, francium; Group 1; periods 2, 3, 4 etc. [3]
2. Any three: soft (can be cut with a knife); low density (float on water); shiny when freshly cut; conduct heat/electricity; low melting/boiling points compared to other metals [3]
3. One outer electron; +1 ions [2]
4. Alkali metals react with oxygen and moisture in air; oil prevents contact with air/water, reducing risk of oxidation or fire [2]
5. Metal oxide [1]
6. a) 4Li + O₂ → 2Li₂O b) 4Na + O₂ → 2Na₂O c) 4K + O₂ → 2K₂O (accept K₂O₂ for potassium peroxide) [3]
7. Any two: floats; fizzes/bubbles; moves on surface; melts to a ball; heat produced; sodium disappears; solution becomes alkaline [2]
8. Alkali metal + water → metal hydroxide + hydrogen [1]
9. a) 2Li + 2H₂O → 2LiOH + H₂ b) 2Na + 2H₂O → 2NaOH + H₂ c) 2K + 2H₂O → 2KOH + H₂ [3]
10. Hydrogen; hold a lighted splint to the gas — a squeaky pop confirms hydrogen [2]
11. All react with water to produce hydrogen and a metal hydroxide; similar reactions indicate shared properties/same group/family [2]
12. Li < Na < K [1]
13. Going down the group, atoms are larger; outer electron is further from the nucleus; greater electron shielding from inner shells; nuclear attraction on outer electron is weaker; outer electron is lost more easily [3]
14. Any two: potassium reacts more vigorously/ignites with a lilac/purple flame; potassium melts faster; more vigorous fizzing; potassium reacts faster [2]
15. More vigorous/possibly explosive reaction than potassium; Rb is larger with more shielding so outer electron is lost even more easily; 2Rb + 2H₂O → 2RbOH + H₂ [3]