Alkali metals

Alkali metals
01 April 2019

The principles of the periodic table are displayed very elegantly when you consider the alkali metals. The elements in this far left-hand column of the table share physical and chemical properties, but the reactions become increasingly more energetic as we move down the group.
This group of elements are ‘soft’ metals that can easily be cut with a knife and can be found in common household products such as table salt (sodium chloride) or batteries (lithium ion). However, they can also form products such as sodium hydroxide, also called caustic soda, which is a strong, corrosive alkali that causes burns to skin and eyes.

If you get some sodium hydroxide on your skin it will cause a chemical reaction called saponification. This process is used to form soaps and will cause a soapy feeling on your skin.

Industrially, these corrosive products are used widely in numerous chemical processes from drain cleaning to pharmaceutical manufacturing. This wide use means that they can be subject to spills during transport or result in human exposures. They are readily soluble in water so copiously flushing the affected area with water is the recommended first aid. 

 A spectacular demonstration of the alkali metal’s reactivity can be seen when they are added to water. Lithium, at the top of the group, will fizz in water with a crimson red flame, whereas sodium produces an intense yellow flame. Many older street lights contain sodium, which gives the characteristic dark yellow glow. Further down the table, the reaction becomes more energetic. Potassium produces a lilac flame, but the reaction is over quickly. Rubidium, caesium and francium are quite rare, but react vigorously in contact with water.

Did you know?

Radioactive rubidium and caesium are used in extremely accurate atomic clocks – if an atomic clock had been started when Tyrannosaurus rex walked the Earth, it would be no more than 1 second off today.

Hydrogen is produced in these reactions with water, which is a highly flammable gas as mentioned in our article on hydrogen and helium (read the article here).

In recent years, NCEC has seen a rise in calls relating to lithium-based batteries, which have been used extensively in many applications ranging from mobile phones to electric vehicles. The high energy density of these batteries has allowed a revolution in mobile technology. However, several incidents have occurred as a result of these batteries short circuiting and overheating. There are other battery technologies based on sodium as well and NCEC provides detailed information regarding this to support the emergency services as part of our national role.

However, to paint this group of elements as hazardous would be doing them an injustice. Potassium hydroxide in combination with manganese dioxide forms purple crystals (potassium permanganate). These crystals have many applications such as being used in the treatment of a number of skin conditions, in water treatments to remove iron and hydrogen sulphide, and in synthesising organic compounds such as ascorbic acid or isonicotinic acid. However, being a powerful oxidiser, it will ignite readily when mixed with glycerol; a useful trait for its inclusion into survival kits as a fire starter. Potassium permanganate can be used to sterilise water as well.

In our next issue we will be discussing the alkali metal’s cousins, magnesium, calcium and beryllium. Their group is called the alkali earth metals. Calcium is an essential element for our health and is involved in bone and blood cell manufacture.

What else can these elements do? Find out next time.