The way any material interacts with a magnetic field is a fundamental property of matter. When a substance is exposed to an external magnetic field, its constituent atoms and electrons react predictably. This interaction is not uniform; some materials are drawn into the field, while others are subtly pushed away. This behavior allows scientists to categorize nearly every known element into one of two primary states: diamagnetism and paramagnetism. These categories are determined by the internal structure of the atom.
Defining Paramagnetism and Diamagnetism
These two magnetic states are defined by their weak, yet distinct, reactions when placed in a magnetic field. Paramagnetic materials exhibit a slight attraction, meaning they are weakly pulled toward the region of highest magnetic field strength. This attraction is not permanent; the material only shows a magnetic moment while the external field is applied. When the field is removed, the temporary magnetism vanishes as thermal energy randomizes the internal magnetic alignment.
In contrast, diamagnetic materials display a weak repulsion from a magnetic field, effectively being pushed away from the strongest part of the field. This repulsive behavior is a universal property of all matter, though it is masked in substances with stronger magnetic tendencies. The induced magnetic field in a diamagnetic substance always points opposite to the applied external field. This repulsion is weak and disappears immediately once the external magnetic influence is withdrawn. The measurable difference lies in their magnetic susceptibility: paramagnetic materials have a small positive susceptibility, while diamagnetic materials have a small negative one.
The Role of Electron Configuration in Magnetism
The magnetic state of an atom is dictated by the arrangement of its electrons within atomic orbitals. Electrons possess spin, which creates a tiny magnetic moment, effectively making each electron a miniature magnet. How these individual magnetic moments combine or cancel determines the atom’s overall magnetic behavior. This behavior is rooted in how electrons fill the available energy subshells.
The presence of unpaired electrons is the mechanism behind paramagnetism. An unpaired electron occupies an orbital alone, and its magnetic moment is free to align, however weakly, with an external magnetic field. The more unpaired electrons an atom possesses, the stronger its paramagnetic attraction will be. Hund’s rule explains that electrons fill separate orbitals with parallel spins before pairing, maximizing the net magnetic moment.
Diamagnetism results when all electrons in an atom are paired. The Pauli exclusion principle dictates that two electrons sharing the same orbital must have opposite spins. These opposing spins cause the magnetic moment of one electron to be canceled out by the magnetic moment of its partner. When every electron is part of such a pair, the atom has a net magnetic moment of zero, leading to the weak repulsion characteristic of diamagnetism.
Determining Magnesium’s Magnetic Property
Magnesium (Mg), with an atomic number of 12, is classified as a diamagnetic element. This determination is based on an analysis of its electron configuration, which describes how its 12 electrons are distributed among the atomic orbitals. The ground state electron configuration for a neutral magnesium atom is written as \(1s^2 2s^2 2p^6 3s^2\). This notation indicates the filling sequence of the first three energy levels.
The first two electrons fill the \(1s\) orbital, the next two fill the \(2s\) orbital, and the subsequent six electrons fill the three \(2p\) orbitals. Crucially, the final two valence electrons fill the \(3s\) orbital. In every one of these orbitals (\(1s\), \(2s\), \(2p\), and \(3s\)), the electrons exist as a pair with opposite spins.
Because the magnesium atom has a full complement of paired electrons, the magnetic moment produced by one electron is nullified by the magnetic moment of its partner. This results in a net magnetic moment of zero for the atom. The absence of unpaired electrons confirms that magnesium exhibits the characteristic weak repulsion from a magnetic field, solidifying its classification as diamagnetic.
Common Examples of Magnetic States in Elements
Magnesium’s diamagnetic nature places it alongside many other elements that have a full outer shell or subshell of electrons. For instance, noble gases like Neon and Argon are diamagnetic because their electron shells are completely filled, leaving no unpaired electrons. Other diamagnetic materials include metals like Copper and Gold, where electron pairing results in a zero net magnetic moment.
In contrast, many common elements are paramagnetic. Oxygen gas, for example, is notably paramagnetic because its molecular orbitals contain two unpaired electrons. Transition metals, like Titanium and Aluminum, are also paramagnetic due to partially filled \(d\) orbitals, which leaves several electrons unpaired and available to generate a net magnetic moment. These examples highlight how differences in electron count and orbital filling are responsible for the range of magnetic responses observed across the periodic table.