Question

What sort of magnetic susceptibility graph would you expect for: (a) \(\mathrm{MnO}\). (b) \(\mathrm{Co}\).

Short answer

(a) For MnO, the magnetic susceptibility graph would show an increase in susceptibility with rising temperature and approach zero as temperature approaches infinity, typical of a paramagnetic substance. (b) For Co, the graph would depict a sharp increase in magnetic susceptibility as the external magnetic field increases, with susceptibility reaching a maximum (saturation) as a ferromagnetic material. Above its Curie temperature, the susceptibility of Co would decrease with increasing temperature, resembling a paramagnetic behavior.

Step-by-step solution

Identification of electronic configurations

First, let's determine the electronic configurations of MnO and Co: (a) MnO (Manganese Oxide) - Mn is a transition metal with an atomic number of 25. Its electronic configuration is \([Ar] 3d^5 4s^2\). The oxidation state of Mn in MnO is +2, which means it loses 2 electrons from the 4s orbital. Thus, the electronic configuration of Mn in MnO is \([Ar] 3d^5\). (b) Co (Cobalt) - Co is a transition metal with an atomic number of 27. Its electronic configuration is \([Ar] 3d^7 4s^2\). Cobalt is a metallic element, so it retains its electronic configuration in the elemental form.

Determine the magnetic properties

Now, let's determine the magnetic properties of MnO and Co based on their electronic configurations: (a) MnO: Manganese ion Mn2+ has an electronic configuration of \([Ar] 3d^5\). All the 5 electrons in the 3d orbital have unpaired spins, which makes the Mn2+ ion paramagnetic. (b) Co: Cobalt has an electronic configuration of \([Ar] 3d^7 4s^2\). There are 3 unpaired electrons in the 3d orbital, which makes cobalt a ferromagnetic material.

Plotting magnetic susceptibility graphs

Now that we know the magnetic properties of MnO and Co, we can describe the expected magnetic susceptibility graphs for them: (a) MnO: Since MnO contains Mn2+ ions which are paramagnetic, we expect its magnetic susceptibility graph to show an increase in magnetic susceptibility with an increase in temperature. The graph should approach zero as temperature approaches infinity. (b) Co: As a ferromagnetic material, cobalt's magnetic susceptibility should exhibit a sharp increase as the external magnetic field increases. The graph should approach saturation, where magnetic susceptibility reaches a maximum. At temperatures above its Curie temperature, the magnetic susceptibility of cobalt will decrease as temperature increases, resembling a paramagnetic substance.

Key concepts

Paramagnetic Materials

Materials that are attracted by an external magnetic field and form internal, induced magnetic fields in the direction of the applied magnetic field are known as paramagnetic materials. These substances do not retain magnetization in the absence of an external field because the magnetism is not locked in alignment.

In paramagnetic materials, atoms or ions have at least one unpaired electron, which means that these electrons spin in such a way that they generate a magnetic moment. The ability of a material to be magnetized in this way is measured as magnetic susceptibility, which is positive for paramagnetic materials. However, it is typically quite small compared to that of ferromagnetic materials.

Common examples include aluminum, oxygen (particularly in the gaseous state), and in the context of our exercise, the Mn2+ ion in manganese oxide (MnO). When the external magnetic field is removed, the magnetization often disappears quickly.

Ferromagnetic Materials

Ferromagnetic materials, on the other hand, are strongly magnetized in the direction of the magnetic field and can retain their magnetic properties even after the external field is removed. This is because the magnetic moments align with each other due to a strong interaction, known as exchange coupling.

The magnetic susceptibility of ferromagnetic materials is not only positive but also quite large, and the materials exhibit a nonlinear relationship between induced magnetization and the applied magnetic field. The magnetic susceptibility increases sharply until it reaches a point called saturation, where an increase in the magnetic field strength no longer results in an increase in magnetization.

Cobalt (Co) is one such material that exhibits ferromagnetism. Typically, ferromagnetic materials will show a permanent magnetic field, making them perfect candidates for permanent magnets. Iron, nickel, and cobalt are the most common examples of ferromagnetic materials.

Electronic Configuration

Electronic configuration is the arrangement of electrons in the orbitals of an atom. Understanding these configurations is crucial for predicting the chemical and magnetic behavior of elements.

The electrons in an atom fill up the orbitals in a specific order, guided by principles like the Pauli exclusion principle, Hund's rule, and the Aufbau principle. These guidelines dictate that each orbital can hold a maximum of two electrons with opposite spins, that electrons will occupy separate orbitals of the same energy before pairing up, and that lower energy orbitals are filled before higher energy orbitals, respectively.

For transition metals, the arrangement of electrons in the 'd' and 's' orbitals is especially important for determining magnetic properties. The presence of unpaired electrons in an element's 'd' orbitals usually leads to paramagnetism or ferromagnetism, depending on the extent of electron pairing and the exchange forces between atomic spins.

Transition Metals

Transition metals are elements in the d-block of the periodic table, known for their unique properties including colorful compounds, variable oxidation states, and magnetic properties. They typically have incomplete d orbitals, which play a key role in their chemistry and physical characteristics.

The electronic configurations of transition metals are (n-1)d1–10 ns1–2, where 'n' represents the principal quantum number. These configurations result in a fascinating array of chemical behaviors, as the d electrons participate in bonding and reactions.

In our example, manganese has an atomic number of 25 and an electronic configuration of [Ar] 3d5 4s2, with manganese in MnO having a +2 oxidation state and a configuration of [Ar] 3d5. Cobalt, on the other hand, with an atomic number of 27, has an electronic configuration of [Ar] 3d7 4s2. Such elements often display a diversity of magnetic properties, with variations seen among different compounds and solid-state structures.