What is the electron configuration of Co²⁺ and how many unpaired electrons are in the free transition metal ion?
(a) [Ar]3d⁵4s²; 5 unpaired electrons
(b) [Ar]3d⁵4s²; 1 unpaired electron
(c) [Ar]3d⁷; 3 unpaired electrons
(d) [Ar]3d⁷; 1 unpaired electron

Verified step by step guidance

1. Determine the electron configuration of a neutral cobalt (Co) atom. Cobalt has an atomic number of 27, so its electron configuration is [Ar]3d^7 4s^2.
2. Identify the change in electron configuration when cobalt forms a Co^{2+} ion. This involves removing two electrons from the neutral atom.
3. Remove electrons starting from the outermost shell, which is the 4s orbital in this case. So, remove the two electrons from the 4s orbital.
4. Write the electron configuration for Co^{2+} after removing the electrons: [Ar]3d^7.
5. Determine the number of unpaired electrons in the 3d^7 configuration. In a 3d^7 configuration, there are 3 unpaired electrons.

Key Concepts

Electron Configuration

Electron configuration describes the distribution of electrons in an atom's orbitals. For transition metals, this involves filling the 3d and 4s orbitals. The notation uses the noble gas core, followed by the specific orbitals and the number of electrons in each, which is crucial for determining the chemical properties and reactivity of the element.

Transition Metals and Oxidation States

Transition metals can exhibit multiple oxidation states due to the involvement of d electrons in bonding. For cobalt (Co), the +2 oxidation state (Co²⁺) results from the loss of two electrons, typically from the 4s orbital first, followed by the 3d orbital. Understanding oxidation states is essential for predicting the electron configuration of ions.

Unpaired Electrons and Magnetism

Unpaired electrons in an atom or ion contribute to its magnetic properties. The presence of unpaired electrons can lead to paramagnetism, where the substance is attracted to magnetic fields. Counting unpaired electrons is vital for understanding the behavior of transition metal ions in various chemical contexts, including their reactivity and bonding.