MP Board · Class 10 · Science · Periodic Classification of ElementsDiscuss the trends in properties of elements along a period and down a group in the Modern Periodic Table. Explain any four properties: Valency, Atomic Radius, Metallic-Non-metallic character, and Electronegativity.

1. Valency

• Along a Period: When moving from left to right across a period, the number of valence electrons increases from 1 to 8. The valency first increases from 1 to 4 and then decreases to 0 (for noble gases).
• Down a Group: The valency remains the same down a group because all elements in a group have the same number of valence electrons.

2. Atomic Radius

• Along a Period: Atomic radius generally decreases from left to right across a period. This is because the nuclear charge increases, pulling the electrons closer to the nucleus and decreasing the size of the atom.
• Down a Group: Atomic radius increases down a group. As we go down, a new shell is added successively, increasing the distance between the outermost electrons and the nucleus, thus increasing the atomic size.

3. Metallic and Non-Metallic Character

• Along a Period: Metallic character decreases from left to right across a period, while non-metallic character increases. This happens because the effective nuclear charge increases, making it harder for atoms to lose electrons and easier to gain them.
• Down a Group: Metallic character increases down a group, and non-metallic character decreases. The outer electrons are further from the nucleus and are lost more easily due to shielding effect and increased distance.

4. Electronegativity

• Along a Period: Electronegativity increases across a period from left to right due to decreasing atomic radius and increasing nuclear charge, which enhances the tendency to attract shared electron pairs.
• Down a Group: Electronegativity decreases down a group because the atomic size increases, reducing the nucleus's attractive pull on shared electrons.