The Alkali Metals
We call the first group (Group 1) of the Periodic Table the Alkali Metals. This group consists of the metals Lithium, Sodium, Potassium, Rubidium, Caesium and Francium.
All of the Alkali Metals are very reactive. They have to be stored in oil to stop them reacting with oxygen in the air. Their reactivity increases as we move down the group. So Lithium is the least reactive alkali metal and Francium the most reactive.
All of the alkali metals have a very low density for metals. In fact, Lithium, Sodium and Potassium will all float on water. The alkali metals are also all very soft, so we can cut them with a knife. They all have the silvery, shiny look of typical metals when we cut them. However, they quickly go dull as they react with oxygen in the air to form a layer of oxide.
The Group 1 metals also melt and boil at relatively low temperatures. As we go down the group, the melting and boiling points get lower and lower.
The properties of this rather unusual group of metals are the result of their electronic structure. The alkali metals all have one electron in their highest energy level, which gives them similar properties. It also makes them very reactive, as they only need to lose one electron to obtain a stable electronic structure.
They react with non-metals, losing their single outer electron and forming a metal ion carrying a +1 charge. They always for ionic compounds.
The Alkali Metals
When we add Lithium, Sodium or Potassium to water, the metal floats on the water, moving around and fizzing. The fizzing happens because the metal reacts with the water to form Hydrogen Gas. Potassium reacts to vigorously with the water that the Hydrogen produced in the reaction catched fire. It burns with a Lilac flame.
The reaction between the alkali metal and water also produces a metal hydroxide. The hydroxides of the alkali metals are all soluble in water, producing a colourless solution with a high pH.