Physical Properties of Alkali Metals
|Name||Proton number||Electron arrangement|
- All Group 1 metal exist as solid at room temperature and hence have all the typical metallic properties, such as:
- good conductors of heat
- good conductors of electricity,
- high boiling points,
- shiny surface (but rapidly tarnished by air oxidation).
- Nevertheless, Group 1 metals also show some non-typical metallic properties, such as:
- low melting points,
- low density (first three floats on water),
- very soft (easily squashed, extremely malleable, can be cut by a knife).
Important trends down the group:
- size of atoms increases
- the melting point and boiling point decrease
- the density increases.
- the hardness decreases.
Size of Atom
- Down the group, the size of atom increases.
- This is due to the increase in the number of electron shells.
- An atom with more shells is bigger than an atom with fewer shells.
Boiling Point and Melting Point
|Name||melting point||boiling point||Density g/cm3|
- The melting point and boiling point generally decrease down the group.
- All the atoms of Group 1 metals are bonded together by a force called the metallic bond.
- The strength of the metallic bond depends on the distance between the atoms. The closer the atoms, the stronger the bond.
- Down the group, the size of the atoms increases, causing the distance of the atoms increases.
- As the distance between the atoms increases, the metallic bond between the atoms decreases.
- Therefore, less energy is needed to overcome the metallic bond during the melting process.
- Consequently, the melting point of Group 1 metal decreases down the group.
- The densities of Group 1 metals are low compared with the other metals.
- The densities of the first 3 elements (Lithium, Sodium and Potassium) are lower than water. Thus, they can float on the surface of the water.
- Nevertheless, the density increases steadily down the group.
- The density of a substance is given by the equation “Density=Mass/Volume”.
- Down the group, both the mass and the volume increase, but the increase of mass is faster than the volume, hence the density increases down the group