Alkali Metals

Mechanical Engineering

The first column on the periodic table of the chemical elements is collectively called the alkali metals. These metals include lithium, sodium, potassium, rubidium, cesium, and francium. Because their outer electron structure is similar, they all have somewhat similar chemical and physical properties. Some of the properties of alkali metals are

  • All the metals are shiny
  • They are so soft that they can be cut with a knife
  • Most of them are white (cesium is yellow-white).
  • All react with water to give hydrogen gas and the metal hydroxide.
  • They also react with the oxygen in the air to give either an oxide, peroxide or superoxide depending on the metal.
  • These metals almost always form ions with a positive (+1) charge.

Sodium is the most abundant, followed by potassium, rubidium, lithium, and cesium. Francium is intensely radioactive and very rare.

Most of the alkali metals glow with a characteristic color when placed in a flame; lithium is bright red, sodium gives off an intense yellow, potassium is violet, rubidium is a dark red, and cesium gives off blue light.


Lithium (Li) was discovered in 1817 by J.A. Arfvedson, but the free metal was not isolated until 1821, by W.T. Brande. It is the smallest alkali metal, with an atomic number of 3 and an atomic weight of 6.94 amu (atomic mass unit). It has a melting point of 356.9°F (180.5°C), and a boiling point of 2,457°F (1,347°C).

Uses of Lithium: Lithium is used in lubricants, in batteries, in glass industries, and in alloys of lead, aluminum, and magnesium to make them less dense and stronger.


Sodium (Na) is the second element in the alkali metal group, with an atomic number of 11 and an atomic weight of 22.9898 amu. Its melting point 208°F (97.8°C) and boiling point 1,621.4°F (883°C) are both lower than those of lithium. Humphry Davy first isolated sodium metal by passing electricity through molten sodium hydroxide in 1807. It occurs naturally, in compound form, in relatively large amounts—about 20,000 parts per million in the earth’s crust. Sodium chloride (or common salt) is one of the most common compounds on Earth, followed closely by sodium carbonate (also called soda ash or washing soda).

Uses of sodium:

  • Sodium nitrite is a principle ingredient in gunpowder.
  • The pulp and paper industry uses large amounts of sodium hydroxide, sodium carbonate, and sodium sulfate.
  • Sodium carbonate is used by power companies to absorb sulfur dioxide, a serious pollutant, from smokestack gases.
  • Sodium carbonate is also used in the glass and detergent industries.
  • Sodium chloride is used in foods and to soften the water.
  • Sodium bicarbonate (baking soda) is produced for the food industry as well.


Potassium (K), the third element in the alkali metal group, has an atomic number of 19 and an atomic mass of 39.0983 amu. Its melting point and boiling point are 145.9°F (63.28°C) and 1,398.2°F (759°C) respectively. Davy discovered and isolated potassium in 1807, by passing electricity through molten potassium hydroxide to obtain the free metal.

Uses of potassium:

  • Most of the Potassium is used in making the fertilizer.
  • Potassium hydroxide is used the detergent.
  • Potassium chlorate is used in explosive.
  • Potassium bromide is used in photography industries.

Rubidium and cesium:

Rubidium (Rb), the fourth element in the alkali metal group, has an atomic number of 37 and an atomic weight of 85.4678 amu. Its melting point is 102.8°F (39.31°C), and its boiling point is 1,270.4°F (688°C).

Cesium (Cs), the second to last element in the group, has an atomic number of 55, an atomic weight of 132.9054 amu, a melting point of 83.12°F (28.40°C), and a boiling point of 1,239.8°F (671°C).

Both were discovered in 1860-1861 by R.W. Bunsen and G.R. Kirchoff. They were the first two elements to be discovered with a spectroscope.

Uses of Rubidium and cesium: Rubidium is used almost exclusively for research, but cesium is used in special glasses and radiation detection equipment.


Marguerite Perey discovered francium (Fr) in 1939. Almost no francium occurs naturally on the earth, except very small amounts in uranium ores. It is very radioactive, so the very tiny amounts produced by bombarding radium with neutrons are used almost exclusive exclusively for pure research.