The group 1 elements in the periodic table are known as the alkali metals. They include lithium, sodium and potassium, which all react vigorously with air and water.
The reactivity of the alkali metals increases down the group. Flame tests are used to identify alkali metal ions in compounds.
The group 1 elements are placed in the vertical column on the left hand side of the periodic table.
Lithium, sodium and potassium are the three group 1 elements you are likely to see at school. Like all the group 1 elements, they are very reactive. They must be stored under oil to keep air and water away from them. Group 1 elements form alkaline solutions when they react with water, which is why they are called alkali metals.
Reactions with Water
Group 1 elements react vigorously with water to produce an alkaline metal hydroxide and hydrogen gas. In general:
Metal + water → metal hydroxide + hydrogen
For example, here are the equations for the reaction of sodium with water:
sodium + water → sodium hydroxide + hydrogen 2Na + 2H2O → 2NaOH + H2 (the 2s in front of Na, H2O and NaOH are for balancing)
The reactivity of the alkali metals increases down the group. Lithium is the least reactive and potassium is the most reactive of the three. The hydrogen ignites immediately during the reaction between potassium and water with the potassium producing a lilac coloured flame.
The group 1 elements become more reactive as you go down the group. At the top, lithium is the least reactive and francium at the bottom is the most reactive. Francium is rare and radioactive, so it would be difficult to confirm predictions made about it. However, it is possible to predict the properties of rubidium and caesium and to see if the predictions were accurate.
Group 1 elementMelting point/ °C Lithium 181 Sodium 98 Potassium 63 Rubidium 39 Caesium 29
Flame colourIon present Red Lithium Orange Sodium Lilac Potassium