Alkali metals

• Group 1 elements


  Alkali metals
• Alkali metals


  • Relatively soft
  • Low densities
  • Low melting points
  • Much more reactive than other metals
  • React vigorously with water, oxygen, and group 7 elements
• As you go down the group


  • Elements become even more reactive
  • Melting points and boiling points decrease
• Common table salt (sodium) doesn't suddenly catch fire when sprinkled on potatoes, unlike cesium
• Reactivity


  How easily atoms can lose or gain electrons and react with other atoms
• Alkali metals almost always form ionic compounds with non-metals
• Ionic compounds


  Where a metal atom donates an electron to a non-metal, forming oppositely charged ions that are attracted by electrostatic forces
• Ionic compounds are generally white solids that tend to dissolve in water to form colorless solutions
• Reaction of alkali metals with water


  1. Produces metal hydroxide and hydrogen gas

  2. Becomes more vigorous going down the group, igniting the hydrogen
• Reaction of alkali metals with chlorine


  1. Forms white metal chloride salts

  2. Becomes more vigorous going down the group
• Reaction of alkali metals with oxygen


  1. Forms metal oxides

  2. Type of oxide depends on the metal (e.g. lithium oxide, sodium oxide, sodium peroxide, potassium peroxide, potassium superoxide)
• Don't need to know why the particular oxide compounds form, just need to memorize them
• Lithium


  • Moves on the water surface
  • Bubbles
  • Heat released
  • Disappears at the end of the reaction
  • Colourless solution produced
• Sodium


  • Melts into a tiny ball
  • Moves on the water surface
  • Bubbles
  • Heat released
  • Disappears at the end of the reaction
  • Colourless solution produced
  • Lilac flame
• Potassium


  • Melts into a tiny ball
  • Moves on the water surface
  • Bubbles
  • Heat released
  • Disappears quickly
  • Colourless solution produced
  • Crackles at end
• Lithium + water


  Lithium hydroxide + hydrogen
• Sodium + water


  Sodium hydroxide + hydrogen
• Potassium + water


  Potassium hydroxide + hydrogen
• Lithium, sodium, and potassium


  • They all react with water in similar ways: fizz, release hydrogen gas, and form hydroxides
  • This consistent behavior indicates they belong to the same group, Group 1 or alkali metals
• Lithium reacts more slowly with water


  Compared to sodium and potassium
• Trend in reactivity within Group 1


  Variations in how alkali metals react with air and water
• Based on what we know about lithium, sodium, and potassium, we can make educated guesses about the properties of other alkali metals like rubidium and cesium
• If other alkali metals follow the same trend, we can expect them to behave similarly in reactions with water, air, and other substances
• Trend in reactivity within Group 1


  Can be explained by looking at the electronic configurations of these elements
• Alkali metals


  Have one electron in their outermost energy level, which they readily give away to form positive ions
• Ease with which alkali metals lose their outermost electron


  Determines their reactivity
• Elements with fewer electrons in their outermost shell, like lithium


  Are less reactive compared to those with more electrons, like potassium
• The trend in reactivity within Group 1 can be understood by examining how easily these elements lose their outermost electron to achieve a stable electronic configuration