Group 1 Elements – Alkali Metals

  1. The Group 1 metals is called the Alkali Metals.
  2. This is because they form oxides and hydroxides that dissolve in water to give alkaline solutions.
  3. As shown in the diagram on the right, elements in this group are lithium, sodium, potassium, rubidium, caesium and francium.
  4. They are the first element of a period, with one valence electron.
  5. This similarity (1 valence electron) makes them chemically behave in a similar manner.
  6. All alkali metals are very reactive. They must be stored in oil prevent reaction with oxygen or water vapour in air.

Physical Properties of Alkali Metals

NameProton numberElectron arrangementmelting pointboiling pointDensity g/cm3
Lithium32.1180ºC1342ºC0.53
Sodium112.8.198ºC883ºC0.97
Potassium192.8.8.163ºC759ºC0.86
Rubidium372.8.18.8.139ºC688ºC1.48
Caesium552.8.18.18.8.129ºC671ºC1.87
Francium872.8.18.32.18.8.127ºC677ºC> 1.87
  1. All Group 1 metal exist as solid at room temperature and hence have all the typical metallic properties, such as:
    1. good conductors of heat
    2. good conductors of electricity,
    3. high boiling points,
    4. shinny surface (but rapidly tarnished by air oxidation).
  2. Nevertheless, Group 1 metals also show some non-typical metallic properties, such as:
    1. low melting points,
    2. low density (first three float on water),
    3. very soft (easily squashed, extremely malleable, can be cut by a knife).

Important trends down the group:

  1. size of atoms increases
  2. the melting point and boiling point decrease
  3. the density increases.
  4. the hardness decreases.
Size of Atom
  1. Down the group, the size of atom increases.
  2. This is due to the increase of number of electron shells.
  3. Atom with more shells is bigger than atom with less shells.

Boiling Point and Melting Point

  1. The melting point and boiling point generally decrease down the group.
  2. All the atoms of Group 1 metals are bonded together by a force called metallic bond.
  3. The strength of metallic bond depends on the distance between the atoms. The closer the atoms, the stronger the bond.
  4. Down the group, the size of the atoms increases, causing the distance of the atoms increases.
  5. As the distance between the atoms increases, the metallic bond between the atoms decreases.
  6. Therefore, less energy is needed to overcome the metallic bond during melting process.
  7. Consequently, the melting point of Group 1 metal decreases down the group.

Density

  1. The densities of Group 1 metals are low compare with the other metals.
  2. The densities of the first 3 elements (Lithium, Sodium and Potassium) are lower than water. Thus, they can float on the surface of water.
  3. Nevertheless, the density increases steadily down the group.
  4. Density of a substance is given by the equation “Density=Mass/Volume”.
  5. Down the group, both the mass and the volume increase, but increase of mass is faster than the volume, hence the density increases down the group

Chemical Properties of Alkali Metals


    1. Group 1 metals are very reactive metals.
    2. They all show the same chemical properties.
    3. They can react with water and non-metal such as oxygen and chlorine to form a new compound.
    4. The table to the right shows the electron arrangement of all the Group 1 metals. All the atoms of Group 1 metal consist of 1 valence electron.
    5. When an alkali metal atoms react, it loses the valence electron to form a positively charged ion. 
Example:
    Li→L i + +e Na→N a + +e K→ K + +e
  1. They tend to react mainly with non-metals to form ionic compounds.

Safety Precaution

  1. Alkali metals are very reactive.
  2. Therefore it must be kept in paraffin oil to prevent them from reacting with oxygen and water vapour in the air.
  3. We must avoid to hold group 1 metals with bare hand because they may react with water on our hand.
  4. We must wear safety goggles and gloves during handling experiment involving group 1 metal.

Alkali Metals React with Chlorine

    1. All alkali metals react with chlorine gas to form white metal chlorides salt.

    Group 1 Metals + Chlorine Gas → Metal Chloride

      1. The metal chlorides salt formed is soluble in water to give a neutral solution of pH 7.
      2. The reactivity increases down the group from lithium, sodium to potassium.

      Example:

      Lithium + Chlorine

      2Li + Cl2 → 2LiCl

      Observation
      Lithium burned slowly with a reddish flame . A white solid is produced.

      Sodium + Chlorine

      2Na + Cl2 → 2NaCl

      Observation
      Sodium burned brightly with a yellowish flame. A white solid is produced.

      Potassium + Chlorine

      2K + Cl2 → 2KCl

      Observation
      Potassium burned very brightly with a purplish flame . A white solid is produced.

      Alkali Metals React with Oxygen

        1. Group 1 metals react with oxygen gas produces metal oxides. These metal oxides dissolve in water produces alkalis.

      Group 1 Metals + Oxygen Gas → Metal Oxide
      1. Lithium, sodium and potassium form white oxide powders after reacting with oxygen.
      2. The white powder is the oxide of lithium, sodium and postassium.
      3. When the white powder is dissolved in water, it produces a solution which turned red litmus paper blue. Which means, these oxides dissolve in water to form strong alkali.
      4. The reactivity increases down the group from lithium, sodium to potassium.
      Example

      Lithium + Oxygen

      4Li + O2→ 2Li2O

      Dissolve in water

      Li2O + H2O → 2LiOH

      Observation
      Lithium burns with red flame and produces white powder immediately after reaction.

      Sodium + Oxygen

      4Na + O2→ 2Na2O

      Dissolve in water

      Na2O + H2O → 2NaOH

      Observation
      Sodium burned with bright yellow flame, forming white powder immediately after reaction.

      Potassium + Oxygen

      4K + O2→ 2K2O

      Dissolve in water

      K2O + H2O → 2KOH

      Observation
      Potassium burned with very bright purplish flame, forming white powder immediately after reaction.



      Alkali Metals React with Water

      Group 1 metals react vigorously with water produces alkali and hydrogen gas

      Group 1 Metals + Water → Alkali + Hydrogen gas

      Common Observation

        1. Lithium, sodium or potassium floats and move around on the surface of the water and then dissolve in the water.
      Conclusion
          : Lithium, sodium and potassium are less dense than water.
        1. Colourless gas is released around the metal. The gas produces a “pop” sound when ignited with lighted wooden splinter.
      Conclusion
          : The colourless flammable gas is hydrogen.
        1. The solution turn blue when it is tested with universal indicator.
      Conclusion
        : the solution produced is an alkali.

      Lithium + Water


      2Li + 2H2O → 2LiOH + H2

      Observation
      Lithium metal moves slowly on the surface of water with ‘fizzing’ sound.

      Sodium + Water


      2Na + 2H2O → 2NaOH + H2

      Observation
      The lump of sodium moves swiftly on the surface of water with ‘fizzing’ sound

      Potassium + Water


      2K + 2H2O → 2KOH + H2

      Observation
      Potassium reacts violently with water, move very fast on the surface of water and burn with lilac flame.

      Explaining the Reactivity Trend of the Alkali Metals

      1. When an alkali metal atom reacts, it loses its valence electron to form a positively charged ion.
      2. Example
        Li → Li+ + e
        Na → Na+ + e
        K → K+ + e
      3. As we go down the group from one element down to the next, the atomic radius gets bigger due to an extra filled electron shell.
      4. The valence electron is further and further from the nucleus. Thus the attraction force between the nucleus and the valence electron become weaker and weaker.
      5. This causes the valence electron is easier to be released to form an ion when the atom takes part in a reaction.


      Solubility of the Oxide, Hydroxide and Salt of Alkali Metals

      1. All the oxide and hydroxide of group 1 metal are soluble in water to form an alkali solution.
      2. All the salts (salt of chloride, nitrate, sulphate, carbonate….) of group 1 metals are soluble in water. The solutions formed are neutral.