Question

A sudden large jump between the values of second and third ionization energies of an element would be associated with which of the following electronic \(\begin{aligned}&\text { configuration? } \\\&\text { (a) } 1 s^{2}, 2 s^{2} 2 p^{6}, 3 s^{1} 3 p^{2} & \text { (b) } 1 s^{2}, 2 s^{2} 2 p^{6}, 3 s^{2} 3 p^{1}\end{aligned}\) (c) \(1 s^{2}, 2 s^{2} 2 p^{6}, 3 s^{1}\) (d) \(1 s^{2}, 2 s^{2} 2 p^{6}, 3 s^{2}\)

Short answer

(c) and (d)

Step-by-step solution

Understanding Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in the gas phase. The first ionization energy is the energy needed to remove the first electron, the second is for the second electron, and so on. A large jump in ionization energy occurs when a core electron, which is closer to the nucleus and thus more tightly bound, is removed after the valence electrons are removed.

Analyzing the Given Electron Configurations

Inspect each configuration to determine the number of valence electrons and which electron would be removed during the third ionization. Valence electrons are in the highest energy levels or outermost shells and the first to be removed.

Identifying the Configuration with the Large Jump

The configuration with a large jump between the second and third ionization energies will be one where the first two electrons are valence electrons, and the third is a core electron. This is typically when removing an electron from a fully filled or half-filled noble gas configuration.

Matching the Configuration to the Options

Option (a) has 3 valence electrons and would still have valence electrons after two are removed. Option (b) has 3 valence electrons as well, similarly having valence electrons after two removals. Option (c) has 1 valence electron and the third ionization would remove from a complete octet, indicating a large jump. Option (d) has 2 valence electrons, and only after these are removed would the third ionization target the complete octet, also indicating a large jump.

Determining the Correct Answer

Option (c) and (d) are the correct answer because they are associated with the removal of a tightly bound core electron after the valence electrons have been removed. The second and third ionization energies in option (c) and (d) involve moving from the removal of valence electrons to that of core electrons, which requires significantly more energy.

Key concepts

Electron Configuration

Understanding electron configuration is crucial when discussing ionization energy and other atomic properties. Electron configuration describes how electrons are distributed in an atom's orbitals according to the quantum mechanical models of atomic structure. Electrons fill orbitals in a way that minimizes the energy of the atom. This typically follows the Aufbau principle, which states that electrons occupy the lowest energy orbitals first.

For example, hydrogen has one electron, which goes into the lowest energy orbital, the 1s orbital, giving it the electron configuration of \(1s^1\). Helium, with two electrons, fills the 1s orbital completely, resulting in the configuration \(1s^2\). As we move to larger elements, electrons begin to fill in the 2s, 2p, 3s, and so forth, in a pattern informed by their increasing energy levels.

It's also essential to be aware of electron configurations because they determine an element's chemical behavior. During the ionization process, it's the arrangement of these electrons that dictates which electron will be easier or harder to remove.

Valence Electrons

Valence electrons are the electrons in the outermost shell, or energy level, of an atom. These electrons play a key role in chemical reactions because they can be gained, lost, or shared in the formation of chemical bonds. For instance, in the configuration \(1s^2 2s^2 2p^4\), the valence electrons would be the six electrons in the second energy level (2s and 2p orbitals).

Typically, atoms tend to follow the octet rule, striving for a set of eight valence electrons, which is a stable electron configuration similar to that of noble gases. Valence electrons are significant because the first ionization energy involves the removal of one of these less tightly bound, more reactive electrons. When these are removed, and a core electron must be removed next, a noticeable increase in ionization energy is observed.

Core Electrons

Core electrons are the electrons that are not in the outermost energy level of an atom; these are the ones that fill the inner shells. They are generally well shielded by the valence electrons and are not involved directly in the formation of chemical bonds. Core electrons are more tightly bound to the nucleus due to their closer proximity and lower energy levels.

For example, in the argon atom with an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6\), the first 10 electrons (1s, 2s, and 2p orbitals) are considered core electrons. The removal of a core electron typically requires a significantly higher amount of energy than the removal of a valence electron because of the lower energy and higher nuclear charge acting on these inner-shell electrons, leading to the large jumps in ionization energy as observed in our exercise.