Group 1 Elements - Alkali Metals

1. The Group 1 metals is called the Alkali Metals.
2. This is because they form oxides and hydroxides that dissolve in water to give alkaline solutions.
3. As shown in the diagram on the right, elements in this group are lithium, sodium, potassium, rubidium, caesium and francium.
4. They are the first element of a period, with one valence electron.
5. This similarity (1 valence electron) makes them chemically behave in a similar manner.
6. All alkali metals are very reactive. They must be stored in oil prevent reaction with oxygen or water vapour in air.

Physical Properties of Alkali Metals

Name	Proton number	Electron arrangement	melting point	boiling point	Density g/cm3
Lithium	3	2.1	180ºC	1342ºC	0.53
Sodium	11	2.8.1	98ºC	883ºC	0.97
Potassium	19	2.8.8.1	63ºC	759ºC	0.86
Rubidium	37	2.8.18.8.1	39ºC	688ºC	1.48
Caesium	55	2.8.18.18.8.1	29ºC	671ºC	1.87
Francium	87	2.8.18.32.18.8.1	27ºC	677ºC	> 1.87

1. All Group 1 metal exist as solid at room temperature and hence have all the typical metallic properties, such as:
1. good conductors of heat
2. good conductors of electricity,
3. high boiling points,
4. shinny surface (but rapidly tarnished by air oxidation).
2. Nevertheless, Group 1 metals also show some non-typical metallic properties, such as:
1. low melting points,
2. low density (first three float on water),
3. very soft (easily squashed, extremely malleable, can be cut by a knife).

Important trends down the group:

1. size of atoms increases
2. the melting point and boiling point decrease
3. the density increases.
4. the hardness decreases.

Size of Atom

1. Down the group, the size of atom increases.
2. This is due to the increase of number of electron shells.
3. Atom with more shells is bigger than atom with less shells.

Boiling Point and Melting Point

1. The melting point and boiling point generally decrease down the group.
2. All the atoms of Group 1 metals are bonded together by a force called metallic bond.
3. The strength of metallic bond depends on the distance between the atoms. The closer the atoms, the stronger the bond.
4. Down the group, the size of the atoms increases, causing the distance of the atoms increases.
5. As the distance between the atoms increases, the metallic bond between the atoms decreases.
6. Therefore, less energy is needed to overcome the metallic bond during melting process.
7. Consequently, the melting point of Group 1 metal decreases down the group.

Density

1. The densities of Group 1 metals are low compare with the other metals.
2. The densities of the first 3 elements (Lithium, Sodium and Potassium) are lower than water. Thus, they can float on the surface of water.
3. Nevertheless, the density increases steadily down the group.
4. Density of a substance is given by the equation "Density=Mass/Volume".
5. Down the group, both the mass and the volume increase, but increase of mass is faster than the volume, hence the density increases down the group

Chemical Properties of Alkali Metals

1. Group 1 metals are very reactive metals.
2. They all show the same chemical properties.
3. They can react with water and non-metal such as oxygen and chlorine to form a new compound.
4. When an alkali metal atoms react, it loses the valence electron to form a positively charged ion. 
Example:

Li→Li++eNa→Na++eK→K++e
5. They tend to react mainly with non-metals to form ionic compounds.

Safety Precaution

1. Alkali metals are very reactive.
2. Therefore it must be kept in paraffin oil to prevent them from reacting with oxygen and water vapour in the air.
3. We must avoid to hold group 1 metals with bare hand because they may react with water on our hand.