Materials react differently when encountering a magnetic field. Some substances, like iron, show a strong attraction, while others appear unaffected. This behavior is determined by the material’s atomic structure. To classify aluminum (Al), we must examine its fundamental properties and atomic structure.
Defining Paramagnetism and Diamagnetism
Diamagnetic substances exhibit a weak repulsion when placed near a magnet. This means the material will move away from both the north and south poles of a powerful magnet.
Paramagnetic materials, conversely, show a weak attraction to an external magnetic field. Unlike the strong attraction seen in common iron magnets, this pull is extremely subtle and can only be measured with specialized scientific equipment. The key distinction is that both diamagnetic and paramagnetic responses are weak and temporary, disappearing once the external magnetic field is removed.
The underlying cause for these classifications is the effect the magnetic field has on the motion of electrons within the atoms. The difference between attraction and repulsion depends on the inherent magnetic moments within the atoms.
Electron Configuration and Unpaired Electrons
The most important factor determining a material’s magnetic property is the arrangement of electrons within its atoms. Electrons orbit the nucleus and also spin on their axis, and each of these movements creates a tiny magnetic moment. When two electrons occupy the same orbital, they must have opposite spins, which causes their individual magnetic moments to cancel each other out completely, resulting in a net magnetic moment of zero.
Materials where all electrons are paired in this way are classified as diamagnetic. However, if an atom contains one or more unpaired electrons, the net spin is no longer zero, and the atom possesses a permanent, though small, magnetic moment. The presence of even a single unpaired electron is enough to classify a substance as paramagnetic.
Aluminum, with an atomic number of 13, has a specific electron configuration that determines its magnetic behavior. The full configuration is \(1s^2 2s^2 2p^6 3s^2 3p^1\). The first 12 electrons are paired across the \(1s\), \(2s\), \(2p\), and \(3s\) orbitals. However, the final electron resides alone in the \(3p\) orbital, meaning the aluminum atom has an overall magnetic moment.
The Magnetic State of Aluminum
Given the presence of the single unpaired electron, aluminum is classified as a paramagnetic material. When an external magnetic field is applied, the individual magnetic moments of these unpaired electrons align themselves with the field, causing the weak, temporary attraction characteristic of paramagnetism.
Because there is only one unpaired electron per atom, the overall magnetic attraction is extremely slight. This is why a piece of aluminum foil or an aluminum can does not visibly stick to a refrigerator magnet.
If aluminum is placed in a very strong, non-uniform magnetic field, its paramagnetic behavior becomes demonstrable. The material will be weakly drawn toward the region of highest magnetic field strength, confirming its classification.