Question

The atomic numbers of \(\mathrm{V}, \mathrm{Cr}, \mathrm{Mn}\) and \(\mathrm{Fe}\) are respectively \(23,24,25\) and 26 . Which one of these may be expected to have the highest second ionization enthalpy? (a) \(\mathrm{V}\) (b) \(\mathrm{Cr}\) (c) \(\mathrm{Mn}\) (d) \(\mathrm{Fe}\)

Short answer

Cr is expected to have the highest second ionization enthalpy due to stable half-filled d configuration post first ionization.

Step-by-step solution

Understand Ionization Enthalpy

Ionization enthalpy is the energy required to remove an electron from an atom in its gaseous state. The second ionization enthalpy is the energy needed to remove a second electron after the first one has been removed. It is generally higher for atoms with stable electronic configurations after the first ionization.

Determine Electronic Configurations

Find the electronic configurations for - V (23): [Ar] 3d^3 4s^2 - Cr (24): [Ar] 3d^5 4s^1 - Mn (25): [Ar] 3d^5 4s^2 - Fe (26): [Ar] 3d^6 4s^2. Post ionization (first electron removed), the configurations are: - V+: [Ar] 3d^3 4s^1 - Cr+: [Ar] 3d^5 (half-filled stable d) - Mn+: [Ar] 3d^5 4s^1 - Fe+: [Ar] 3d^6 4s^1

Analyze Stability After First Ionization

A half-filled or fully filled d subshell is particularly stable. Hence, Cr+ with its half-filled 3d^5 configuration is quite stable, making it more energy costly to remove another electron and achieve Cr2+. Mn+ and Fe+ don't have that stability advantage post-first ionization.

Compare with the Context of Second Ionization

The stability of the electron configuration heavily influences ionization enthalpy. Cr+, having a stable half-filled d subshell after the 1st ionization, will have a high second ionization enthalpy since removing another electron would destabilize its electronic configuration.

Key concepts

Second Ionization Enthalpy

When we talk about the second ionization enthalpy, we're discussing the energy required to remove a second electron from an atom that is already positively charged. After the first electron is taken away, the atom becomes a cation with a +1 charge. Removing a second electron means overcoming even more attraction between the electron and the now-more positively charged nucleus.
In general, the second ionization enthalpy is always higher than the first ionization enthalpy. This is because once the first electron is removed, the remaining electrons are more strongly attracted to the nucleus. Therefore, a stable electronic configuration after the first ionization can make the second ionization more energy-intensive.
When analyzing which element might have the highest second ionization enthalpy, we must look at their electronic configuration after the first electron has been removed. A particularly stable arrangement, like a half-filled or full d subshell, makes removing the next electron more difficult.

Electronic Configuration

An element's electronic configuration describes the distribution of electrons in its orbitals. It follows the pattern of filling from the lowest energy level to the highest. For transition metals, this typically involves filling d orbitals after 4s.
For example, the electronic configurations of V, Cr, Mn, and Fe are:

• V (23): [Ar] 3d^3 4s^2
• Cr (24): [Ar] 3d^5 4s^1
• Mn (25): [Ar] 3d^5 4s^2
• Fe (26): [Ar] 3d^6 4s^2

When you remove the first electron, the energy states change. For instance, Cr becomes [Ar] 3d^5, a half-filled and therefore more stable configuration. This stability influences the second ionization enthalpy. Evaluating such configurations helps us assess which atom resists further electron removal. During ionization, it's important to remember that filled and half-filled orbitals provide stability.

Transition Metals

Transition metals, found in the central block of the periodic table, have partially filled d subshells. These elements are known for their unique properties such as varied oxidation states and a capacity to form complex compounds. Their electronic configurations allow them to behave in diverse ways, especially during ionization.
As transition metals, elements like V, Cr, Mn, and Fe demonstrate variable ionization enthalpies due to their d-electron arrangements. For example, Cr, with a 3d^5 configuration after losing one electron, stands out due to the half-filled stability. This configuration means that Cr resists further ionization, as doing so would disrupt a favorable electron arrangement.
In general, understanding the electronic configuration of transition metals aids in predicting their chemistry and the energy required for further electronic changes. These trends across the transition series elucidate why certain elements exhibit high second ionization enthalpies, as seen with Cr.

Ionization Energy Trends

Ionization energy refers to the amount of energy required to remove an electron from an atom. Trends in ionization energies can often be explained by looking at the periodic table. As you move across a period (left to right), ionization energy increases because electrons are added to the same energy level while the nuclear charge increases, pulling them closer.
However, in transition metals, this trend can be less straightforward due to the filling of d orbitals. Half-filled and fully filled subshells provide enhanced stability. For instance, Cr+ with a 3d^5 configuration does not easily lose another electron because removing one disrupts the stable half-filled arrangement.

• The energy required for such a disruption is reflected in a higher second ionization enthalpy.
• Comparatively, elements without such stable arrangements post-first ionization will generally have lower second ionization enthalpies.

Ultimately, recognizing these patterns enables better predictions of how elements behave during ionization steps.