2.1 Group 1 (Alkali Metals) – Lithium, Sodium and Potassium

REVISION NOTES

IGCSE Edexcel Chemistry

2.1 Group 1 (Alkali Metals) – Lithium, Sodium and Potassium

2.1.1 Understand how the similarities in the reactions of these elements with water provide evidence for their recognition as a family of elements

Group 1 metals (alkali metals) are found in the 1st group (column) of the periodic table. They form alkaline solutions when they react with water.

Because they have same number of electrons in the outer shell, they have similar chemical properties.

Soft metals which can easily be cut with a knife
Low densities
Low melting point
Very reactive

2.1.2 Understand how the differences between the reactions of these elements with air and water provide evidence for the trend in reactivity in Group 1

REACTION WITH WATER

They form alkalis in water, this is why group 1 is called alkali metal
Reaction of alkali metals with water is more vigorous down the group

Group 1 metal + Water → Metal hydroxide + Hydrogen

2M (s) + 2H2O (l) → 2MOH (aq) + H2 (g)

Observations during Group 1 Metal reaction with Water:

Metal disappears or melts
Metal turns into a round ball
Metal floats on water surface
Effervescence (bubbling)
Flame produced (for more reactive Group 1 Metals, lower down the group)

REACTION WITH OXYGEN

Reaction of alkali metals with oxygen is more vigorous down the group
Alkali metals react with oxygen in the air forming metal oxides
- The metal oxide produced covers the surface of the metal as a coating

2.1.3 Use knowledge of trends in Group 1 to predict the properties of other alkali metals

TRENDS IN CHEMICAL PROPERTIES OF ALKALI METALS

Reaction with water and oxygen gets more vigorous down the group (from 2.1.2)

TRENDS IN PHYSICAL PROPERTIES OF ALKALI METALS

Alkali metals get softer down the group
- Due to increasing atomic size and decreasing metallic bond down the group
Melting point >decreases down the group
- Due to decreasing attraction forces between the outer shell electrons and nuclei down the group

PREDICTING PROPERTIES IN GROUP 1

As the reactivity of alkali metals increases down the group:
- Lithium is the least reactive
- Francium would be the most reactive
According to the trend, rubidium (Rb), caesium (Cs) and francium (Fr) react even more vigorously with water and oxygen compared to first three alkali metals
We could also predict rubidium:
- Is a soft solid metal
- Is shiny when freshly cute
- Is more dense than potassium
- Has a lower melting point than potassium