Question

Write the condensed ground-state electron configurations of these transition metal ions, and state which are paramagnetic: (a) \(\mathrm{Mo}^{3+}\) (b) \(\mathrm{Au}^{+}\) (c) \(\mathrm{Mn}^{2+}\) (d) \(\mathrm{Hf}^{2+}\)

Short answer

(a) [Kr] 4d^3, Paramagnetic (b) [Xe] 4f^14 5d^{10}, Diamagnetic (c) [Ar] 3d^5, Paramagnetic (d) [Xe] 4f^14 5d^2, Paramagnetic

Step-by-step solution

- Identify Atomic Numbers

Find the atomic numbers for Mo, Au, Mn, and Hf. - Mo: 42- Au: 79- Mn: 25- Hf: 72

- Write Neutral Atom Configurations

Write out the ground-state electron configurations for each neutral atom using condensed notation.- Mo: [Kr] 4d^5 5s^1- Au: [Xe] 4f^14 5d^10 6s^1- Mn: [Ar] 3d^5 4s^2- Hf: [Xe] 4f^14 5d^2 6s^2

- Remove Electrons for Ions

Remove the appropriate number of electrons from the ground-state configurations to form the ions. Remember that electrons are removed first from the outermost shell:- Mo^{3+}: Remove 3 electrons (first from 5s and then from 4d): [Kr] 4d^3- Au^{+}: Remove 1 electron from the 6s: [Xe] 4f^14 5d^10- Mn^{2+}: Remove 2 electrons (from 4s): [Ar] 3d^5- Hf^{2+}: Remove 2 electrons (first from 6s): [Xe] 4f^14 5d^2

- Determine Paramagnetism

Check whether the ions are paramagnetic (unpaired electrons present):- Mo^{3+} (3 unpaired electrons in 4d): Paramagnetic- Au^{+} (no unpaired electrons): Diamagnetic- Mn^{2+} (5 unpaired electrons in 3d): Paramagnetic- Hf^{2+} (2 unpaired electrons in 5d): Paramagnetic

Key concepts

Condensed Electron Configurations

To write the condensed electron configuration, you first need to know the atomic number of the element, which tells you the number of electrons in a neutral atom. For transition metals, the electrons are filled in a specific sequence based on increasing energy levels. This is known as the Aufbau principle.
For example, the condensed electron configuration for a neutral molybdenum (Mo) atom, which has an atomic number of 42, is [Kr] 4d^5 5s^1. This means that after the core electrons (which are the same as krypton in this case), there are five electrons in the 4d orbital and one in the 5s orbital.
When forming ions, electrons are removed starting with the outermost shell. For instance, to obtain the configuration for Mo^{3+}, you remove three electrons from the neutral configuration, starting with the 5s and then the 4d orbital, resulting in [Kr] 4d^3. This method can be applied to other transition metals to find their respective condensed electron configurations.

Paramagnetism

Paramagnetism occurs in an atom or ion when there are unpaired electrons present. Unpaired electrons produce a magnetic field, causing the ion to be attracted to an external magnetic field.
To check for paramagnetism, look at the electron configuration of the ion and count the number of unpaired electrons. For example, Mn^{2+} has the configuration [Ar] 3d^5. Since there are five unpaired electrons in the 3d orbital, Mn^{2+} is paramagnetic.
In contrast, Au^{+} has the configuration [Xe] 4f^14 5d^10. All the electrons are paired in this case, making Au^{+} diamagnetic. Understanding whether an ion is paramagnetic can help in predicting its chemical and physical properties such as reactivity and magnetic behavior.

Transition Metals

Transition metals are elements found in the d-block of the periodic table, spanning from groups 3 to 12. They are known for having incomplete d-subshells either in their elemental state or in their ions.
These elements exhibit a variety of oxidation states and unique properties such as high melting points, conductivity, and the ability to form complex ions. The presence of d-electrons allows transition metals to form colored compounds and to engage in catalytic activity.
Key examples include elements like iron (Fe), copper (Cu), and molybdenum (Mo). Transition metals are crucial not just in industrial applications but also in biological systems. For example, iron is a key component of hemoglobin in blood, which is essential for oxygen transport.
Understanding the electron configurations of transition metals is fundamental, as it affects their chemical bonding, reactivity, and the types of compounds they form.