The oxidation number of lead (Pb) in lead(II) oxide (PbO) is +2.
Understanding Oxidation Numbers
An oxidation number (or oxidation state) is a measure of the degree of oxidation of an atom in a chemical compound. It represents the hypothetical charge an atom would have if all its bonds were purely ionic. Assigning oxidation numbers helps in understanding how electrons are transferred in chemical reactions, particularly in redox (reduction-oxidation) reactions.
Rules for Determining Oxidation Numbers
To accurately determine the oxidation number of an element within a compound, specific rules are followed. For compounds like PbO, two key rules are applied:
- The Sum of Oxidation Numbers: In a neutral compound, the sum of the oxidation numbers of all atoms is zero.
- Oxidation Number of Oxygen: Oxygen typically has an oxidation number of -2 in its compounds. There are a few exceptions, such as in peroxides (e.g., H₂O₂, where it's -1), superoxides (e.g., KO₂, where it's -½), and when bonded to fluorine (e.g., OF₂, where it's +2).
Calculating the Oxidation Number of Pb in PbO
Let's apply these rules to determine the oxidation number of Pb in PbO:
- PbO is a neutral compound, so the sum of the oxidation numbers of Pb and O must be zero.
- In PbO, oxygen is not in any of the exceptional cases (it's not a peroxide, superoxide, or bonded to fluorine). Therefore, its oxidation number is the common -2.
Let $x$ be the oxidation number of Pb. The equation for the sum of oxidation numbers in PbO is:
$x$ (for Pb) + (-2) (for O) = 0
Solving for $x$:
$x - 2 = 0$
$x = +2$
Thus, the oxidation number of lead (Pb) in PbO is +2.
Summary of Oxidation Numbers in PbO
The following table summarizes the oxidation numbers for each element in the compound PbO:
| Element | Oxidation Number |
|---|---|
| Oxygen (O) | -2 |
| Lead (Pb) | +2 |
The positive oxidation number for lead indicates that it has effectively lost two electrons to the more electronegative oxygen atom in this compound. Understanding these assignments is fundamental to studying chemical reactivity and balancing redox equations. For more information on assigning oxidation numbers, you can refer to resources like Chemistry LibreTexts or Khan Academy.
