Question

Would you expect the reaction of \(\mathrm{Pb}(\mathrm{s})\) and \(\mathrm{Cl}_{2}(\mathrm{g})\) to yield \(\mathrm{PbCl}_{2}\) or \(\mathrm{PbCl}_{4} ?\)

Short answer

Under normal conditions, the reaction between Pb(s) and Cl2(g) commonly yields PbCl2, due to its stability and less reactivity.

Step-by-step solution

Identify the Oxidation State of Lead

Lead (Pb) can have two common oxidation states: +2 and +4. These states refer to the number of electrons that an atom loses or gains when it gets oxidized or reduced.

Use the Octet Rule

Chlorine (Cl) has an oxidation state of -1. This means it needs one more electron to satisfy the octet rule, which states that atoms are most stable when their outer electron shell is full, typically with 8 electrons. From this, we can see that one Pb atom will combine with either 2 or 4 Cl atoms, depending on its oxidation state.

Determine the Compound Formed

Both PbCl2 and PbCl4 are possible compounds, depending on the reaction conditions. However, PbCl2 is more common under normal conditions because it is more stable and less reactive. PbCl4 can exist, but it is less stable and more reactive.

Key concepts

Oxidation States

Understanding the oxidation states of elements is crucial when predicting the products of chemical reactions. The oxidation state, also known as the oxidation number, is an indicator of the degree of oxidation or reduction of an atom in a chemical compound. Essentially, it tells us how many electrons an atom has lost or gained. For example, lead (Pb) can have oxidation states of +2 and +4. A positive oxidation state indicates that the atom has lost electrons, becoming a cation. In reactions between metals and non-metals, like lead (Pb) reacting with chlorine gas (Cl₂), we can determine the likely products by considering the common oxidation states of the reacting elements.

In the exercise, knowing that lead can either lose two or four electrons (corresponding to the +2 or +4 oxidation states) allows us to hypothesize the formation of either PbCl₂ or PbCl₄. To decide which compound is more likely to form, we must consider other factors such as the stability of the resulting compounds and the octet rule, which influence the likelihood of each scenario.

Octet Rule

The octet rule is a fundamental concept in chemistry that helps us understand how atoms bond together to form molecules. It is based on the principle that atoms tend to combine in such a way that each atom has eight electrons in their valence shell, which results in a spherically shaped electron cloud that is energetically stable. An atom will typically share, gain, or lose electrons to achieve a complete octet, resembling the electron configuration of a noble gas.

In the context of our exercise, chlorine (Cl) with an oxidation number of -1 is seven electrons short of a complete octet. Therefore, it 'desires' to acquire one more electron to fulfill this rule. When pairing chlorine with lead (Pb), one Pb atom could either share two electrons to form PbCl₂, satisfying the octet rule for two chlorine atoms, or share four electrons to form PbCl₄, satisfying the octet rule for four chlorine atoms. The actual compound formed reflects a balance between the octet rule and the overall stability of the product, which brings us to the importance of compound stability in chemical reactions.

Compound Stability

Compound stability plays a significant role in predicting the products of a chemical reaction. Stability depends on various factors, including the nature of the atoms involved, the distribution of charge, and the molecular structure. Generally, the more stable a compound, the more likely it is to form under a given set of conditions. Conversely, less stable compounds are typically more reactive and can decompose or react further under certain circumstances.

In the reaction between lead (Pb) and chlorine gas (Cl₂), we consider the stability of the potential products, PbCl₂ and PbCl₄. Under normal conditions, the divalent PbCl₂ is more stable due to its favorable charge distribution and the lower energy required to form the Pb²⁺ ion. Tetravalent PbCl₄, while possible, is a less stable compound because it involves a Pb⁴⁺ ion, which has a higher charge and thus faces more significant repulsion within the molecule, leading to decreased stability.

In summary, the factors of oxidation states, octet rule compliance, and compound stability collectively influence which compounds are likely to result from a chemical reaction.