Question

Two atoms have the electron configurations \(1 s^{2} 2 s^{2} 2 p^{6}\) and \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\). The first ionization energy of one is \(2080 \mathrm{~kJ} / \mathrm{mol}\), and that of the other is \(496 \mathrm{~kJ} / \mathrm{mol}\). Match each ionization energy with one of the given electron configurations. Justify your choice.

Short answer

Neon has \(2080 \text{kJ/mol}\), and sodium has \(496 \text{kJ/mol}\).

Step-by-step solution

Identify the Electron Configurations

The electron configurations given are for two atoms. The first configuration is \(1 s^{2} 2 s^{2} 2 p^{6}\), which corresponds to a fully filled second energy level, often characteristic of a noble gas like neon. The second configuration is \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\), which corresponds to sodium, with one electron in the 3s orbital.

Understand Ionization Energy

Ionization energy is the energy required to remove the outermost electron from an atom in its gaseous state. Noble gases like neon have high ionization energies due to their stable electron configuration, whereas elements with a single electron in their outer shell, like sodium, have lower ionization energies because it's easier to remove that lone outer electron.

Match Ionization Energies

The noble gas configuration \(1 s^{2} 2 s^{2} 2 p^{6}\), matching neon, will have the higher ionization energy of \(2080 \text{kJ/mol}\) due to its full shell stability. The sodium configuration \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\), will have the lower ionization energy of \(496 \text{kJ/mol}\) as it is easier to remove its single 3s electron.

Justify the Match

Neon's filled 2p orbital resists losing an electron, resulting in a high ionization energy of \(2080 \text{kJ/mol}\). Sodium, with its unpaired electron in the 3s orbital, has a lower ionization energy of \(496 \text{kJ/mol}\) because that electron is less strongly held by the nucleus.

Key concepts

Electron Configuration

Understanding electron configuration is key to chemistry and understanding the behavior of atoms. An atom's electron configuration describes the number and arrangement of electrons in its shells and subshells. This configuration is important because it determines how atoms interact with each other.

For instance, in the exercise, the configuration \(1s^{2} 2s^{2} 2p^{6}\) refers to a fully filled second energy level, where the electrons occupy the 1s, 2s, and 2p orbitals. Each "s" subshell can hold a maximum of two electrons, while each "p" subshell can hold up to six. When these subshells are filled, the atom achieves a stable state.

By contrast, the configuration \(1s^{2} 2s^{2} 2p^{6} 3s^{1}\) includes an extra electron in a new "3s" shell. This additional electron significantly influences the atom's chemical properties and its first ionization energy.

Noble Gases

Noble gases, like neon, are elements characterized by their full electron shells. This configuration makes them exceptionally stable and non-reactive. In a noble gas, like the configuration \(1s^{2} 2s^{2} 2p^{6}\), the absence of partially filled shells results in minimal tendency to gain or lose electrons.

One of the standout features of noble gases is their high ionization energies. This is because removing an electron from a full and stable electron shell requires a lot of energy. The electron arrangement in noble gases leads to a low level of chemical reactivity, as they usually do not need to attain stability by sharing or exchanging electrons with other atoms.

Removal of Outermost Electron

Ionization energy is directly related to the removal of an atom's outermost electron. This measure indicates how much energy is needed to pull away that electron. The ease or difficulty of this process depends heavily on the electron configuration of the atom.

In sodium's configuration, \(1s^{2} 2s^{2} 2p^{6} 3s^{1}\), the single outer "3s" electron is relatively less tightly bound to the nucleus. This makes it easier to remove, resulting in a lower ionization energy of \(496 \text{kJ/mol}\).

By comparison, the electron in a noble gas configuration is much more strongly attached due to the filled and stable shells, thus making its removal require significantly more energy.

Stability of Electron Shells

The stability of electron shells plays a crucial role in determining an atom's reactivity and ionization energy. A full electron shell, like in noble gases, means the electrons are symmetrically distributed and experience a balanced attraction from the nucleus.

• This balance minimizes the atom's inclination to react with other elements.
• The resultant stability makes it difficult for another atom or external influence to disrupt the arrangement.
• The more stable an electron configuration, the higher the energy required for ionization.

Sodium's electron configuration \(1s^{2} 2s^{2} 2p^{6} 3s^{1}\) highlights this concept, as the lone "3s" electron is less integrated into the stable core, leading to greater susceptibility to removal.