How to know valencies of elements of variable valencies in a compound? Ex- lead oxide. Here what should we take the valency of lead?

Determining the valency of elements with variable valencies in compounds can be a bit tricky, but with a systematic approach, it becomes manageable. Let's take lead oxide as an example to illustrate how to find the valency of lead in this compound.

Understanding Variable Valencies

Some elements, particularly transition metals and certain post-transition metals, can exhibit more than one valency. This means they can form compounds with different charges depending on the context. Lead (Pb) is one such element, commonly found in two oxidation states: +2 and +4.

Identifying the Compound

In the case of lead oxide, we need to first recognize the formula, which is typically represented as PbO. The "O" stands for oxygen, which has a known valency of -2. This is a crucial piece of information because it helps us deduce the valency of lead in this compound.

Calculating the Valency

To find the valency of lead in lead oxide, we can use the principle of charge balance. The total positive charge from lead must equal the total negative charge from oxygen in the compound. Here’s how we can break it down:

• The valency of oxygen is -2.
• Let’s denote the valency of lead as "x."
• In a neutral compound, the sum of the charges must equal zero. Therefore, we can set up the equation:

x + (-2) = 0

Solving for x gives us:

x = +2

Conclusion on Lead's Valency

Thus, in lead oxide (PbO), the valency of lead is +2. This means that lead is in the +2 oxidation state in this particular compound. If we were to consider another compound, such as lead(IV) oxide (PbO₂), we would find that lead has a valency of +4 in that case, as the oxygen would contribute a total charge of -4 (2 oxygen atoms at -2 each).

Practical Tips for Identifying Valencies

When dealing with elements that have variable valencies, here are some practical tips:

• Refer to the periodic table for common oxidation states.
• Look at the compound's formula and identify the known valencies of other elements.
• Use charge balance to deduce the unknown valency.
• Familiarize yourself with common compounds and their oxidation states.

By following these steps, you can confidently determine the valency of elements with variable valencies in various compounds. This method not only applies to lead but can be used for other elements as well, making it a valuable skill in chemistry.