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Physical properties of alkali metals.

Answer Text:
Physical properties of alkali metals.
1. Appearance.
- Alkali metals have metallic luster when freshly cut. This refers to a shiny appearance on the cut surface.
- This surface however tarnishes due to reaction on exposure to air.
2. Ease of cutting.
- They are soft and easy to cut.
- The softness and ease of cutting increase down the group.
Reason:
- Alkali metals have giant metallic structures held together by metallic bonds.
- Metallic bond is due to attraction between the positively charged nucleus of one atom and the electrons in the outermost energy level of the next atom.
- Thus the force of attraction is stronger is smaller atoms than in larger atoms.
- The increase in atomic radius down the group implies that the strength of metallic bonds also decrease down the group (hence ease of cutting and softness).
3. They have relatively low melting and boiling points (in comparison to other metals).
Reason: they have relatively weaker metallic bonds.
- The melting and boiling points decrease down the group.
Reason: - The size of the atoms increase down the group due to increasing number of energy levels hence decrease in the strength of the metallic bonds (down the group).
4. Electrical conductivity.
- Alkali metals are good conductors of heat and electricity.
Reason: they have delocalized electrons in the outermost energy level.
- The electrical conductivity is similar for all alkali metals.
Reason: all alkali metals have the same number of delocalized electron (a single electron) in the outermost energy level.
Note:
- In metals the electrons in the outermost energy level do not remain in one fixed position. They move randomly throughout the metallic structure and are thus said to be delocalized.
Ionization energy.

- The number of ionization energies an element may have is equivalent to the number of valence electrons.
- The first ionization energy is the minimum energy required to remove the first electron from the outermost energy level of an atom in its gaseous state.
- The first ionization among alkali metals decreases down the group.
Reason:
- The effective force of attraction of on the outermost electron by the positive nucleus decreases with increasing atomic size and distance from the nucleus.
- Note that the atomic radius increases down the group due to increase in the number of energy levels.