Periodicity of Valence or Oxidation States of Elements

Introduction to Periodicity of Valence States

Valency is a measure of an element’s ability to combine with other elements. It is defined by the number of electrons an atom needs to gain or lose to achieve a stable electron configuration.

What is an Oxidation State?

The oxidation state of an atom indicates the number of electrons gained or lost by it.

Valency and oxidation states are key properties of elements, determined by their electron configurations. Valency is the number of electrons an atom must lose or gain to achieve stability, while the oxidation state is the charge of an atom due to electron loss or gain.

Valency and Oxidation State

Valence electrons are those in an atom’s outermost shell and define its valency. For elements in the s-block and p-block of the periodic table, valency is often calculated as either the number of valence electrons or eight minus that number.

For d-block and f-block elements, valency depends on both valence electrons and electrons in d and f orbitals, with common valencies being 2 and 3.

Valency of the First 30 Elements in the Periodic Table

Here’s a table listing the valency of the first 30 elements based on their electron configurations:

This table summarizes the valency of the first 30 elements, showing how many electrons each element can gain, lose, or share to form a stable electron configuration.

Trends in Oxidation States

Across a Period: Moving left to right, the number of valence electrons increases from 1 to 8. Valency increases from 1 to 4 and then decreases to zero when combined with hydrogen or oxygen. For example, in Na2O and F2O, F is more electronegative than O in F2O, giving F a -1 oxidation state and O a +2. In Na2O, O is more electronegative, giving O a -2 oxidation state and Na a +1.

Within a Group: The number of valence electrons remains constant down a group, so elements in the same group have the same valency.

Guidelines for Assigning Oxidation States

• Elements in their natural form (O2, H2, etc.) have an oxidation state of zero.
• Oxygen typically has an oxidation state of -2, except in peroxides where it is -1.
• Hydrogen is usually +1, but -1 in metal hydrides (e.g., NaH).
• Halogens are generally -1 unless combined with oxygen or each other.
• Alkali metals (Na, K, etc.) have an oxidation state of +1.
• Alkaline earth metals (Mg, Ca, etc.) have an oxidation state of +2.

Finding Valency of Elements

Valency is determined by the number of electrons in the outer shell. One method to find valency is by consulting the periodic table, where elements in the same group typically have the same valency. For instance, elements in group 8 have a valency of 8, indicating high stability.

By understanding these basic principles, the periodic trends in valency and oxidation states of elements can be easily comprehended.

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