Concept Explanation: Oxidation States

Oxidation state (or oxidation number) indicates the degree of oxidation of an atom in a chemical compound. Some elements show only one non-zero oxidation state, meaning they consistently form compounds with the same oxidation number (other than zero in their elemental form).

Step 1: Understand the Question

We are given the elements: O, Cl, F, N, P, Sn, Tl, Na, Ti. We need to identify how many of these show only one non-zero oxidation state.

Step 2: Recall Common Oxidation States

Let's analyze each element:

• Oxygen (O): Common oxidation states are -2 (e.g., H₂O), -1 (peroxides, e.g., H₂O₂), and +2 (OF₂). So, it shows multiple non-zero states.
• Chlorine (Cl): Shows -1, +1, +3, +5, +7 (e.g., HCl, HClO, HClO₂, HClO₃, HClO₄). Multiple states.
• Fluorine (F): Always -1 in compounds (e.g., HF, NaF). Only one non-zero oxidation state.
• Nitrogen (N): Shows -3 (NH₃), +1 (N₂O), +2 (NO), +3 (N₂O₃), +4 (NO₂), +5 (HNO₃). Multiple states.
• Phosphorus (P): Shows -3, +3, +5 (e.g., PH₃, PCl₃, PCl₅). Multiple states.
• Tin (Sn): Shows +2 and +4 (e.g., SnCl₂, SnCl₄). Multiple states.
• Thallium (Tl): Shows +1 and +3 (e.g., TlCl, TlCl₃). Multiple states.
• Sodium (Na): Always +1 in compounds (e.g., NaCl, Na₂O). Only one non-zero oxidation state.
• Titanium (Ti): Shows +2, +3, +4 (e.g., TiCl₂, TiCl₃, TiO₂). Multiple states.

Step 3: Identify Elements with Only One Non-Zero Oxidation State

From the analysis:

• Fluorine (F): Only -1
• Sodium (Na): Only +1

All others show at least two different non-zero oxidation states.

Final Answer

The number of elements showing only one non-zero oxidation state is 2 (Fluorine and Sodium).

Related Topics

• Oxidation-Reduction Reactions
• Periodic Trends in Oxidation States
• Electronegativity and Oxidation Number
• Stable Oxidation States in Transition Metals

Important Formulae and Theory

Oxidation State Rules:

• The oxidation state of a free element is 0.
• For monatomic ions, it equals the charge.
• Fluorine is always -1.
• Oxygen is usually -2 (except peroxides and OF₂).
• Hydrogen is +1 with non-metals and -1 with metals.
• Alkali metals are always +1; alkaline earth metals are +2.

Example Calculation: In H₂SO₄, oxidation state of S is calculated as: