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C3.4.9 Alkali Metals

C3.4.9 Alkali Metals. Discovery of the Alkali Metals . In 1800, John Dalton produced the first table of the ‘elements’. . Less reactive metals like copper , lead and iron had been discovered but not the alkali metals. .

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C3.4.9 Alkali Metals

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  1. C3.4.9 Alkali Metals

  2. Discovery of the Alkali Metals In 1800, John Dalton produced the first table of the ‘elements’. Less reactive metals like copper, lead and iron had been discovered but not the alkali metals. An element is a substance that can’t be broken down into anything simpler by chemical methods. Soda (now known to be a compound of sodium) and potash (now known to be a compound of potassium) were considered to be elements because they couldn’t be broken down into anything simpler (at that time).

  3. Discovery of the Alkali Metals In 1807, Humphrey Davy passed an electric current through molten potash.

  4. Discovery of the Alkali Metals At the cathode: He observed ‘small globules with a metallic lustre CATHODE -ve ANODE +ve ELECTRODES He had discovered potassium metal and shown that potash was NOT an element. Electrolysis of molten potash. A week later he did the same with soda – and discovered sodium.

  5. Electrolysis of potash The potassium ions were attracted to the cathode (-ve electrode)… -ve +ve …and reduced to the metal by gaining an electron at the cathode… K+ K+ K+ K+ Since the temperature is higher than the melting point of potassium it was formed as small silvery globules. K+ + 1e-ɹ K Na+ + 1e-ɹ Na

  6. Location of the Alkali Metals Group 1

  7. Trends of the Alkali Metals Lithium Sodium Reactivity increases Potassium Rubidium Size of the atom increases Caesium Francium

  8. Reaction with water The alkali metals react very vigorously with water but all produce the same type of products: alkali metal + water metal hydroxide + hydrogen Sodium + water sodium hydroxide + hydrogen 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) The hydroxides of the metals are all strongly basic – turn universal indicator purple; pH > 7 Hydrogen burns with a pop when a lighted splint is held near it.

  9. Uses of the alkali metals The alkali metals are far too reactive to use safely, e.g. they can’t be used to construct buildings or make car bodies However, they can be used as the metal in inert atmospheres or as the ion: • sodium vapour is used in street lights; it adds a bright orange glow to the light • lithium ions in rechargeable cells • potassium ions in fertilisers

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