Which ion has a larger atomic radius, Fe2+ or Fe3+? Explain your reasoning.

Verified step by step guidance

1. Step 1: Understand the concept of atomic radius and how it applies to ions. The atomic radius is the distance from the nucleus of an atom to the outermost shell of electrons. For ions, this can change depending on the loss or gain of electrons.
2. Step 2: Consider the electron configuration of neutral iron (Fe). Iron has an atomic number of 26, so its electron configuration is [Ar] 3d^6 4s^2.
3. Step 3: Determine the electron configuration for Fe2+. When iron loses two electrons to form Fe2+, it typically loses the 4s electrons first, resulting in the configuration [Ar] 3d^6.
4. Step 4: Determine the electron configuration for Fe3+. When iron loses three electrons to form Fe3+, it loses the 4s electrons and one 3d electron, resulting in the configuration [Ar] 3d^5.
5. Step 5: Compare the effective nuclear charge and electron-electron repulsion in Fe2+ and Fe3+. Fe3+ has one less electron than Fe2+, leading to less electron-electron repulsion and a greater effective nuclear charge per electron, which generally results in a smaller atomic radius for Fe3+ compared to Fe2+.

Key Concepts

Atomic Radius

The atomic radius is a measure of the size of an atom, typically defined as the distance from the nucleus to the outermost electron shell. It can vary depending on the type of ion or atom, as well as its charge. Generally, cations (positively charged ions) have smaller radii than their neutral atoms due to the loss of electrons and increased effective nuclear charge.

Ion Charge and Size Relationship

The charge of an ion significantly influences its size. When an atom loses electrons to form a cation, the remaining electrons experience a stronger attraction to the nucleus, resulting in a smaller ionic radius. Therefore, comparing ions with different charges, the one with a higher positive charge will typically have a smaller radius due to this increased effective nuclear charge.

Comparison of Fe2+ and Fe3+

In the case of iron, Fe2+ has lost two electrons, while Fe3+ has lost three. The loss of an additional electron in Fe3+ leads to a greater effective nuclear charge acting on the remaining electrons, causing Fe3+ to have a smaller atomic radius than Fe2+. Thus, Fe2+ has a larger atomic radius compared to Fe3+.