The compound which does not show paramagnetism is: (a) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) (b) \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}\) (c) NO (d) \(\mathrm{NO}_{2}\)

Understanding electron configuration is fundamental to studying paramagnetism in chemistry. Electron configuration refers to the distribution of electrons within an atom or molecule, particularly around the nucleus in various atomic orbitals. Think of it as a map that tells us where the electrons are located. An electron configuration follows a specific order based on the energy levels and sublevels (s, p, d, f) within an atom.

For transition metals, such as copper (Cu) and silver (Ag) in our exercise, electron configuration becomes crucial in understanding their chemical behavior, including magnetic properties. Copper, in a +2 oxidation state, has a d9 electron configuration, meaning there are nine electrons in its d-orbital. Since the d-orbital can hold up to ten electrons, the presence of only nine means there is one unpaired electron. This unpaired electron contributes to paramagnetism. On the other hand, silver in a +1 oxidation state is d10, meaning its d-orbital is fully filled with no unpaired electrons.

Understanding how to determine these configurations allows us to predict which compounds are paramagnetic or diamagnetic.

Paramagnetism is directly connected to the presence of unpaired electrons within an atom or molecule. Unpaired electrons are electrons in an atom's orbitals that are alone without a paired electron with opposite spin. Since electrons have a property called spin, and two electrons can occupy the same orbital when they have opposite spins, when an electron is alone, its spin leads to magnetic properties.

Materials with unpaired electrons are attracted to external magnetic fields, which is the essence of paramagnetism. This is observed in both the NO molecule and the copper compound from our exercise, as they both contain unpaired electrons. The attraction to magnetic fields can be measured and used to determine the magnetic moment of the substance, which is a quantitative measure of its paramagnetism. In analyses like our exercise, looking for unpaired electrons is an effective way of identifying if a compound will display paramagnetic properties.

In the world of magnetism, diamagnetism is the other side of the coin compared to paramagnetism. Diamagnetic materials are characterized by the absence of unpaired electrons. This results in them being weakly repelled by a magnetic field. In our exercise, the silver compound \text{\([\text{Ag}(\text{NH}_3)_2]\text{Cl}}\) is an example of a diamagnetic substance due to its complete d10 electron configuration, meaning all electrons are paired, creating a stable and non-magnetic structure.

Diamagnetism can be seen in many chemical elements and compounds, regardless of the presence of a magnetic field, due to their inherent electron pairing. Though weak compared to paramagnetic forces, diamagnetic behavior plays a significant role in magnetic imaging and applications where a magnetic field must be limited or manipulated. Remember, a substance is diamagnetic if it does not get attracted to a magnetic field, which is a direct consequence of having all electrons paired.