The alkali metals share similar physical properties. For example, they:
The table shows the melting points of five alkali metals. Use this information to describe how melting point changes in group 1.
|Element||Melting point (°C)|
Going down group 1, the melting point decreases.
When a group 1 element takes part in a reaction, its atoms each lose one electron. This forms positively charged ions. The ions have a stable arrangement of electrons, with a complete outer shell.
The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water:
sodium + water → sodium hydroxide + hydrogen
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Complete the word equation and balanced symbol equation for the reaction of potassium with water.
potassium + water → ______________ + ______________
2 ___(s) + 2H2O(l) → ___KOH(aq) + ______(g)
potassium + water → potassium hydroxide + hydrogen
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
The table shows observations when lithium, sodium and potassium are added to water. The reactivity of these metals increases going down the group.
|Element||Observation when added to water|
|Lithium, Li||Fizzes steadily; slowly becomes smaller until it disappears|
|Sodium, Na||Fizzes rapidly; melts to form a ball; quickly becomes smaller until it disappears|
|Potassium, K||Burns violently with sparks and a lilac flame; quickly melts to form a ball; disappears rapidly, often with a small explosion|
Rubidium is placed below potassium in group 1. Predict what is seen when rubidium is added to water.
Rubidium melts very quickly. It burns violently and explodes.
The group 1 elements react with oxygen from the air to make metal oxides.
At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.
The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.
sodium + oxygen → sodium oxide
4Na(s) + O2(g) → 2Na2O(s)
The reactivity of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.
Predict which becomes white more quickly on exposure to air - a piece of rubidium, or a piece of lithium. Explain your answer.
The rubidium becomes white more quickly. This is because rubidium is below lithium in group 1, so rubidium is more reactive and so it reacts with the oxygen in the air to form an oxide layer more quickly.
The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides. At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions. For example:
sodium + chlorine → sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
The reactions with chlorine get more vigorous going down the group.
Balance the equation for the reaction of potassium with chlorine.
_____K(s) + Cl2(g) → _____KCl(s)
2K(s) + Cl2(g) → 2KCl(s)
When a group 1 element takes part in a reaction, each of its atoms loses its outer electron to form a positively charged ion. The more easily the ions form, the more reactive the metal.
Going down group 1: