MP Board · Class 10 · Science · Periodic Classification of ElementsDiscuss the periodic trends in chemical reactivity of elements across a period and down a group. Explain how metallic and non-metallic character, valence, and the nature of oxides vary.

Variation of Valence

• Across a Period: The valence of elements increases from 1 to 4 and then decreases to 0 as we move from left to right across a period.
• Down a Group: The valence remains the same for all elements in a given group because they all have the same number of valence electrons.

Metallic and Non-Metallic Character

• Across a Period: Metallic character decreases from left to right across a period, while non-metallic character increases. This happens because the nuclear charge increases, making it harder for atoms to lose electrons and easier to gain electrons.
• Down a Group: Metallic character increases down a group, and non-metallic character decreases. As we move down a group, the atomic size increases, making it easier for atoms to lose valence electrons due to decreased nuclear attraction.

Nature of Oxides

• Basic to Acidic (Across a Period): The oxides of elements on the left side of the periodic table are basic in nature (e.g., Na2O, MgO), whereas the oxides of elements on the right side are acidic in nature (e.g., SO2, Cl2O7). Intermediate elements form amphoteric oxides (e.g., Al2O3, ZnO).
• Down a Group: The basic nature of metallic oxides increases down a group, while the acidic nature of non-metallic oxides decreases or remains consistent with changing oxidation states.