1. Gradation in the Halogen Family (Group 17)
The halogens (F, Cl, Br, I, At, Ts) exhibit a gradual change in physical states as we move down the group:
- Fluorine (F₂) and chlorine (Cl₂) are gases.
- Bromine (Br₂) is a liquid.
- Iodine (I₂) is a solid.
This trend occurs due to increasing molecular size and van der Waals forces, which lead to higher melting and boiling points.
2. Gradation in Alkaline Earth Metals (Group 2)
Alkaline earth metals react with water as follows:
M + 2H₂O → M(OH)₂ + H₂
Where M represents an alkaline earth metal.
Trend in Reactivity:
- Beryllium (Be): Does not react with water.
- Magnesium (Mg): Reacts only with steam.
- Calcium (Ca), Strontium (Sr), and Barium (Ba): React with water at room temperature, with increasing reactivity down the group.
This increase in reactivity occurs because atomic size increases, reducing the effective nuclear charge, making it easier to lose valence electrons and react with water. These gradations in properties highlight the predictable trends within each group of the periodic table.
