Alkali Metals

Properties of Alkali Metals

  • Alkali metals are found in Group 1 of the periodic table. They include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).
  • They are identified by having one electron in their outermost energy level, making them highly reactive. This property also makes them excellent conductors of heat and electricity.
  • Alkali metals are soft and can be cut with a knife. They have low melting and boiling points that decrease down the group.
  • They react strongly with water to form alkaline solutions and hydrogen gas. They also react with oxygen and halogens.

Reaction of Alkali Metals

  • When placed in water, alkali metals react vigorously and move around on the surface, fizzing and producing gas. The reaction becomes more violent as you move down the group.
  • The reaction can be summarised as: 2M + 2H2O → 2MOH + H2, where M represents an alkali metal and OH is hydroxide, forming a basic alkaline solution.
  • Alkali metals also react with oxygen in the air. Lithium forms lithium oxide (Li2O), sodium forms sodium peroxide (Na2O2), and potassium, rubidium, and caesium form superoxides (MO2).

Trends in Alkali Metals

  • The reactivity of alkali metals increases down the group. This is due to the outermost electron being further from the nucleus and thus less tightly held, making it easier to lose and thus more reactive.
  • The melting and boiling points decrease down the group due to the increased distance between the positively charged nucleus and the negatively charged delocalised electrons in the ‘sea’ of electrons.
  • The atomic radius (size) of alkali metals increases down the group as a new energy level (shell) of electrons is added for each successive element.