Problem 88 - General Chemistry: Principles and Modern Applications

Question

Explain why \(\mathrm{Zn}, \mathrm{Cd},\) and \(\mathrm{Hg}\) resemble the group 2 metals in some of their properties.

Step-by-Step Solution

Answer

Zn, Cd, and Hg resemble the group 2 metals in their electron configurations and oxidation states. They have a full inner shell and typically exhibit a +2 oxidation state due to the loss of the two s orbital electrons, much like Group 2 metals.

Step 1: Understanding Transition Metals

Zn, Cd, and Hg are transition metals. Transition metals are elements whose atoms have an incomplete inner shell. They are characterized by multiple oxidation states.

Step 2: Understanding Group 2 Metals

Group 2 metals, also known as alkaline earth metals, have a full inner shell and exhibit a single oxidation state of +2.

Step 3: Electron Configuration of Zn, Cd, Hg

The electron configuration of Zn, Cd, and Hg indicates that they also have a full inner shell. This is because each of these elements has two electrons in their outermost s orbital. Zn = [Ar] 4s2,3d10; Cd = [Kr] 5s2,4d10; Hg = [Xe] 6s2,4f14,5d10.

Step 4: Comparing with Group 2 Metals

Like the group 2 metals, Zn, Cd and Hg also exhibit a single +2 oxidation state. This +2 state arises from the loss of the two s orbital electrons present in their ground state. This implies that they exhibit similar chemical behavior to group 2 metals.

Step 5: Conclusion

Therefore, Zn, Cd and Hg resemble the Group 2 metals in some of their properties because of their electron configuration. They have a full inner shell and exhibit an oxidation state of +2 due to the loss of the two s orbital electrons, much like Group 2 metals.

Key Concepts

Electron Configuration

Electron configuration is a way to describe the arrangement of electrons in an atom. Each element has a unique electron configuration which determines its chemical properties and reactivity. For transition metals like Zn, Cd, and Hg, their electron configuration shows that they have fully filled d orbitals and two electrons in their outermost s orbital.

This is important because these outermost electrons are the ones involved in chemical reactions.

• For zinc (\([\text{Ar}] 4s^2 3d^{10}\)), both the 4s and 3d subshells are filled.
• Cadmium (\([\text{Kr}] 5s^2 4d^{10}\)) follows a similar pattern where the 5s and 4d subshells are full.
• Mercury (\([\text{Xe}] 6s^2 4f^{14} 5d^{10}\)) has its outermost electrons in the 6s orbital being involved.

This tendency for Zn, Cd, and Hg to have a full s subshell resembles the alkaline earth metals' (group 2) electron configuration, making them behave similarly in chemical reactions.

Oxidation States

Oxidation states describe the potential gain or loss of electrons by an element, essentially indicating how that element can interact with others. Transition metals, including Zn, Cd, and Hg, typically show multiple oxidation states, but these three metals predominantly exhibit a +2 oxidation state.

When we say an element has a +2 oxidation state, it has lost two electrons, making it more positive. In Zn, Cd, and Hg, the electrons lost are from their outer s orbital:

• For zinc, the electrons in the 4s subshell are lost.
• Cadmium loses from the 5s subshell.
• Mercury loses from the 6s subshell.

This consistent loss of two electrons is very similar to what we see in alkaline earth metals, which also commonly exhibit a +2 oxidation state due to their s orbital electron configuration.

Alkaline Earth Metals

Alkaline earth metals are located in Group 2 of the periodic table and include elements like beryllium, magnesium, calcium, strontium, barium, and radium. These metals are characterized by having two electrons in their outermost s orbital. This electron configuration makes them very reactive, often sharing their electrons in order to achieve stability.

One of their notable features is that they almost always exhibit a +2 oxidation state in their compounds, which means they lose their two outermost s electrons during chemical reactions to form positive ions. This behavior parallels that of Zn, Cd, and Hg, which also show a +2 oxidation state for the same reason—loss of two s orbital electrons.

The full inner shell and the s orbital configuration in both groups of metals contribute to a similarity in their chemical behavior, which is why transition metals like Zn, Cd, and Hg might mimic some properties of the alkaline earth metals.