Predict the number of unpaired electrons for each of the following.
(c) Zn²⁺
(d) Cr³⁺

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Determine the electron configuration of the neutral atom for each element.

For Zn, the electron configuration is [Ar] 3d^{10} 4s^2.

For Cr, the electron configuration is [Ar] 3d^5 4s^1.

Remove electrons according to the charge of the ion. For Zn^{2+}, remove 2 electrons from the 4s orbital. For Cr^{3+}, remove 3 electrons starting from the 4s orbital and then from the 3d orbital.

Count the number of unpaired electrons in the resulting electron configuration for each ion.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron Configuration

Electron configuration describes the distribution of electrons in an atom's orbitals. It follows the Aufbau principle, which states that electrons fill the lowest energy orbitals first. Understanding the electron configuration of an element is crucial for predicting its chemical behavior, including the number of unpaired electrons.

Unpaired Electrons

Unpaired electrons are those that occupy an orbital alone, without a paired electron of opposite spin. The presence of unpaired electrons is significant because it influences an atom's magnetic properties and reactivity. Atoms with unpaired electrons tend to be more reactive and can form bonds more readily.

Transition Metals and Oxidation States

Transition metals can exhibit multiple oxidation states, which affect their electron configurations. For example, when transition metals lose electrons to form cations, the electrons are typically removed from the outermost s and d orbitals. Understanding how to determine the oxidation state of an element helps in predicting the resulting electron configuration and the number of unpaired electrons.

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