Chemistry > s Block Elements > 2.0 Alkali Metals
s Block Elements
1.0 S-Block Elements
2.0 Alkali Metals
3.0 Anamolous Behaviour of Lithium
4.0 Diagonal Relationship – similarities with magnesium
5.0 Compounds of Sodium
6.0 Alkaline Earth Metals
7.0 Diagonal Relationship – Similarities with Aluminium:
8.0 Anomalous Behaviour of Beryllium
9.0 Compounds of Calcium
2.1 Physical Properties
| Atomic Volume | Increases down the groups Li Na K Rb Cs For example. Atomic Radii of Cs is maximum while that of Li is minimum. | Melting and Boiling point | Decreases down the group Li Na K Rb Cs For example. Electronegativity of Li is maximum while that of Cs is minimum. |
| Atomic Volume | Hardness | ||
| Density | Ionisation Energy | ||
| Radioactivity | Conductivity | ||
| Reducing Power | Electronegativity | ||
| Electropositivity | Solubility of salts having small anions | ||
| Anion Stabilisation | |||
| Solubility of salts having small anions |
1. Atomic radii: It increases on moving down the group as a new shell is progressively added. Although the nuclear charge also increases down the group but the effect of addition of new shells is more predominant due to increasing screening effect of inner field shell, on the valence s-electrons.
2. Ionic radii: Alkali metals change into positively charged ions by losing valence electron. The size of cation is smaller than parent atom of alkali metals. The ionic radii increases with increase in atomic number. $$Li^+ > Na^+ > K^+ > Rb^+ > Cs^+$$
$Li^+$ is extensively hydrated because the charge density is higher in comparison to other alkali metals.
3. Ionization Energy (Ionisation Enthalpy): The first ionization enthalpy of the alkali metals decreases down the group because the size of metal increases due to the addition of new shell along with the increase of screening effect.
4. Reducing Properties: They have low values of reduction potential so have strong tendency to loose electrons and act as strong reducing agent. Reducing character increases from sodium to caesium however lithium is strongest reducing agent.
5. Melting and Boiling points: They are very low because the intermetallic bonds in them are quite weak and this decrease with increases in atomic number down the group.
6. Density: The densities of alkali metals are quite low as compared to other metals. Li, Na, K are even lighter than water. The density increases from Li to Cs.
7. Photoelectric Effect: Alkali metals except lithium exhibit photoelectric effect. The ability to exhibit photoelectric effect is due to low value of ionization energy of alkali metals. Li does not emit photoelectrons because of high value of ionization energy.
8. Hydration Enthalpy: The hydration enthalpies of alkali metal ions decrease with increase in ionic sizes.
$$L^i+> Na^+ > K^+> Rb^+ > Cs^+$$
$Li^+$ has maximum degree of hydration and for this reason lithium salts are mostly hydrated, e.g., $LiCl.2H_2O$.
