Reactions & Reactivity

Specification Point 6.3:

• Describe the reactions of lithium, sodium and potassium with water.

• The Group 1 metals react readily with oxygen and water vapour in air so they are usually kept under oil to stop them from reacting.
• They react vigorously in water to produce an alkaline metal hydroxide solution and hydrogen gas.

Specification Point 6.4:

• Describe the pattern in reactivity of the alkali metals, lithium, sodium and potassium, with water; and use this pattern to predict the reactivity of other alkali metals.

• From observing the reactions of Li, Na and K with water it becomes evident that the reactivity of alkali metals increases as you move down the Group.
• Rubidium, caesium and francium will thus react even more vigorously with air and water.
• Of the alkali metals, lithium at the top of the group is the least reactive and francium which is at the bottom would be the most reactive.
• Francium is extremely rare and radioactive so is difficult to confirm predictions.

Specification Point 6.5:

• Explain this pattern in reactivity in terms of electronic configurations.

• The reactivity of the Group 1 metals increases as you go down the group.
• Each outer shell contains only one electron which is lost during reaction.
• The next shell down automatically becomes the outermost shell and since it is already full, the atom obtains noble gas configuration.

• As you go down Group 1, the number of shells of electrons increases by 1 (Period number increases down the Periodic table).
• This means that the outer electron is further away from the nucleus so there are weaker forces of attraction between the electron and the nucleus.
• Therefore less energy is required to overcome the forces of attraction between the negatively charged electron and the positively charged nucleus.
• This allows the electron to be lost more easily, making each alkali more reactive than the previous one as you go down the Group.

Electron shell diagrams of the first three elements in Group 1