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Alkali metals

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Notes de leçon

Properties of Alkali Metals

  • Alkali metals are in Group 1 of the periodic table.
  • They have low melting points and are soft enough to be cut with a knife.
  • They have low densities and are very reactive.
  • They are stored in oil to prevent contact with air and water.

Trends Down Group 1

  • Reactivity increases as you go down the group.
  • Melting points decrease as you go down the group.
  • Lithium is less reactive than potassium; caesium is even more reactive.

Reaction with Water

  • Alkali metals react strongly with water.
  • The general word equation: alkali metal + water → metal hydroxide + hydrogen.
  • The metal hydroxides are alkaline (pH > 7).
  • Reactions become more fierce down the group.

Examples of Reactions

  • Lithium + water → lithium hydroxide + hydrogen (fizzes).
  • Potassium + water → potassium hydroxide + hydrogen (ignites hydrogen).
  • Caesium + water → caesium hydroxide + hydrogen (very vigorous).

Safety Precautions

  • Demonstrations should be behind a safety screen.
  • Only small amounts of alkali metal should be used.
  • Keep alkali metals stored in oil.

Bohr model of a sodium atom (alkali metal) showing electron configuration 2.8.1.

Na — Bohr model (2,8,1)11p12n

Particle arrangement in solids, liquids, and gases. Alkali metals are solid at room temperature (except mercury).

Particle arrangementSolidLiquidGas

Diapos

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Questions d'entraînement

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  1. 1.Which group of the periodic table are the alkali metals in?

    Easy
    • AGroup 1
    • BGroup 2
    • CGroup 7
    • DGroup 0
  2. 2.Which of the following is a property of alkali metals?

    Easy
    • AThey have low melting points.
    • BThey have high melting points.
    • CThey are very unreactive.
    • DThey are hard and cannot be cut with a knife.
  3. 3.What is the pH of an alkaline solution?

    Easy
    • AGreater than 7
    • BEqual to 7
    • CLess than 7
    • DExactly 7
  4. 4.Why are alkali metals stored in oil?

    Easy
    • ATo keep air and water away from them
    • BTo keep them cool
    • CTo make them easier to cut
    • DTo increase their reactivity
  5. 5.Complete the word equation: alkali metal + water → ?

    Easy
    • Ametal hydroxide + hydrogen
    • Bmetal oxide + hydrogen
    • Cmetal hydroxide + oxygen
    • Dmetal oxide + water
  6. 6.When lithium reacts with water, what causes the fizzing?

    Easy
    • ARelease of hydrogen gas
    • BRelease of oxygen gas
    • CFormation of lithium hydroxide
    • DIgnition of the metal
  7. 7.As you go down group 1, how does the reactivity of alkali metals change?

    Easy
    • AReactivity increases
    • BReactivity decreases
    • CReactivity stays the same
    • DReactivity first increases then decreases
  8. 8.Which alkali metal has a stronger reaction with water: lithium or potassium?

    Easy
    • APotassium
    • BLithium
    • CThey react equally
    • DNeither reacts

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