The Alkali Metals – Group 1 HD

The Alkali Metals – Group 1 The elements in Group 1 of the Periodic Table are called the alkali metals. They include lithium (Li), sodium (Na) and potassium (K). Using your periodic table what other elements are in this group? Appearance and Handling Lithium, sodium and potassium are all soft metals that are easily cut with a scalpel or knife. The freshly cut surface is a shiny, silver colour, but this tarnishes quickly to a dull grey as the metal reacts with oxygen and water in the air. Pieces of such metals are stored in oil to prevent these reactions. The shiny surface of sodium tarnishes more quickly than that of lithium. And potassium tarnishes more quickly than sodium. This shows the increasing reactivity of the metals as we go DOWN the group. Because the alkali metals are so reactive, care has to be taken when using them. They must not be touched because they will react with the water in sweat on the skin. Gloves may be used, and goggles should be worn. Melting and Boiling Points The alkali metals have low melting and boiling points compared to most other metals. Apart from the other alkali metals, only three metals (indium, gallium and mercury) have lower melting points than lithium. You can see from the graph that lithium, at the top of Group 1, has the highest melting point in the group. The melting points then decrease as you go down the group. The boiling points of these alkali metals show a similar pattern to the melting points. Density The density of a substance is a measure of how much mass it has for its size. It is measured in grams/cubic centimetre. The alkali metals have low densities compared to most other metals. (They feel lighter.) You can see from the graph that lithium, at the top of Group 1, has the lowest density in the group. The densities then generally increase as you go down the group.