Write orbital diagrams for each ion and determine if the ion is diamagnetic or paramagnetic. a. Cd2+ b. Au+ c. Mo3+ d. Zr2+
The Correct Answer and Explanation is:
Orbital Diagrams and Magnetic Properties of Ions
a. Cd²⁺ (Cadmium ion)
- Atomic number: 48
- Neutral configuration: [Kr] 4d¹⁰ 5s²
- Cd²⁺ configuration: [Kr] 4d¹⁰
Orbital Diagram:
4d: ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ (10 electrons) – all paired
Magnetism: Diamagnetic
Cd²⁺ has all electrons paired in its 4d subshell, with no unpaired electrons.
b. Au⁺ (Gold(I) ion)
- Atomic number: 79
- Neutral configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s¹
- Au⁺ configuration: [Xe] 4f¹⁴ 5d¹⁰
Orbital Diagram:
5d: ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ (10 electrons) – all paired
Magnetism: Diamagnetic
Au⁺ has a completely filled 5d subshell, hence no unpaired electrons.
c. Mo³⁺ (Molybdenum(III) ion)
- Atomic number: 42
- Neutral configuration: [Kr] 4d⁵ 5s¹
- Mo³⁺ configuration: [Kr] 4d³
Orbital Diagram:
4d: ↑ ↑ ↑ (3 electrons) – each in separate orbitals
Magnetism: Paramagnetic
Mo³⁺ has 3 unpaired electrons in the 4d orbitals, making it paramagnetic.
d. Zr²⁺ (Zirconium(II) ion)
- Atomic number: 40
- Neutral configuration: [Kr] 4d² 5s²
- Zr²⁺ configuration: [Kr] 4d²
Orbital Diagram:
4d: ↑ ↑ (2 electrons) – in separate orbitals
Magnetism: Paramagnetic
Zr²⁺ has 2 unpaired electrons in the 4d orbitals, so it’s paramagnetic.
Summary and Explanation
Magnetism in ions is determined by the presence of unpaired electrons in their electron configuration. Diamagnetic ions have all electrons paired and are repelled by a magnetic field, whereas paramagnetic ions have unpaired electrons and are attracted to magnetic fields.
In Cd²⁺, removing two electrons from neutral cadmium removes both 5s electrons, leaving a full 4d¹⁰ configuration. Since all electrons are paired, it is diamagnetic.
Au⁺, derived from gold, loses the single 6s electron, resulting in a full 5d¹⁰ shell. Like Cd²⁺, this configuration is fully paired and thus diamagnetic.
Mo³⁺, however, loses three electrons—first from 5s and then from the 4d orbitals—resulting in 4d³. These three electrons occupy separate orbitals due to Hund’s rule, leading to three unpaired electrons. Thus, Mo³⁺ is paramagnetic.
Zr²⁺ loses its two 5s electrons, retaining two electrons in the 4d shell. Following Hund’s rule, the electrons occupy separate orbitals, leading to two unpaired electrons, making Zr²⁺ paramagnetic.
This exercise emphasizes the importance of electron configurations, especially in transition metals, where d-orbital electron count dictates magnetic behavior. When determining the configuration of ions, always remove electrons from the outermost (highest n) orbitals first. Understanding how electrons occupy orbitals helps explain not only magnetism but also chemical reactivity and bonding tendencies.
