Question

What is the electron configuration of \(\mathrm{Mg}^{2+}\) ? How does its reactivity compare with neutral Mg? How do the reactivities of \(\mathrm{F}^{-}\)and \(\mathrm{F}\) compare?

Short answer

The electron configuration of \textrm{Mg}^{2+} is 1s^2 2s^2 2p^6. \textrm{Mg}^{2+} is less reactive than neutral Mg due to its full octet, implying greater stability. The reactivities of \textrm{F}^{-}and \textrm{F} differ as \textrm{F}^{-} is less reactive than neutral F because \textrm{F}^{-} has a complete stable octet while neutral F is highly reactive, desiring to gain an electron.

Step-by-step solution

Determine the electron configuration of neutral Magnesium (Mg)

First, identify the atomic number of Magnesium (Mg), which is 12. This means a neutral Mg atom has 12 electrons. The electron configuration for Mg is found by placing the electrons in the orbitals starting from the lowest energy level, following the aufbau principle. Thus, the configuration is: 1s^2 2s^2 2p^6 3s^2.

Determine the electron configuration of the Magnesium ion (\textrm{Mg}^{2+})

When Mg loses two electrons to form a Mg^2+ ion, these electrons are lost from the outermost shell. Removing two electrons from the neutral Mg configuration (1s^2 2s^2 2p^6 3s^2) results in the configuration: 1s^2 2s^2 2p^6.

Compare the reactivity of \textrm{Mg}^{2+} with neutral Mg

The reactivity of an ion compared to its neutral atom can be understood in terms of electron configuration stability and energy. Mg^2+ is less reactive than neutral Mg, as Mg^2+ has a full octet, making it more stable and less likely to react. Neutral Mg, on the other hand, tends to lose electrons to achieve a stable full-octet configuration.

Determine the electron configuration of neutral Fluorine (F)

Fluorine (F) has an atomic number of 9, meaning a neutral fluorine atom has 9 electrons. Following the aufbau principle, we place electrons in the orbitals starting from the lowest energy level. The electron configuration for neutral F thus is: 1s^2 2s^2 2p^5.

Determine the electron configuration of the Fluoride ion (\textrm{F}^-)

Fluorine gains one electron to form the F^- ion. Adding one electron to the 2p orbital of the configuration for neutral F (1s^2 2s^2 2p^5) results in a full octet: 1s^2 2s^2 2p^6.

Compare the reactivity of \textrm{F}^{-} with neutral F

Fluoride ion (F^-) is less reactive than neutral fluorine. F^- has a complete octet, which is a stable configuration and less likely to participate in further chemical reactions. In contrast, neutral fluorine is highly reactive, as it seeks to gain one electron to achieve a stable electron configuration.

Key concepts

Aufbau Principle

The aufbau principle is fundamental to understanding how electrons are arranged in an atom. It tells us that electrons populate orbitals in order of increasing energy, starting with the lowest available energy level. This method provides a logical approach to building up the electron configuration of an element.

For instance, when determining the electron configuration of neutral magnesium (Mg), we start by identifying that it has 12 electrons. According to the aufbau principle, these electrons will fill the 1s orbital first, followed by the 2s and then 2p orbitals, before finally the 3s orbital. With this systematic approach, we arrive at Mg's electron configuration: 1s² 2s² 2p⁶ 3s². When we remove electrons to form Mg²⁺, the last two electrons (from the highest energy level) are taken away, resulting in the configuration: 1s² 2s² 2p⁶.

The aufbau principle is key in predicting and understanding the chemical properties of atoms because the electron configuration determines how an atom will interact with others.

Reactivity of Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net electrical charge. The reactivity of ions is closely related to their electron configuration and the drive to achieve a more stable state. For magnesium, we observe that Mg²⁺ has a full octet (following the removal of two 3s electrons), making it chemically less reactive compared to neutral Mg, which is actively seeking to lose two electrons to attain stability.

When comparing fluoride ion (F⁻) with neutral fluorine (F), the F⁻ ion is less reactive because it has a complete octet, a particularly stable configuration. In contrast, neutral fluorine is one electron short of a full octet and is therefore one of the most reactive elements, eager to gain that additional electron. This intrinsic desire to attain a complete octet underpins much of the reactivity observed in ions. Understanding this can be crucial for students grappling with chemical reactions and periodic trends.

Octet Rule

The octet rule is a principle in chemistry which postulates that atoms are generally most stable when they have eight electrons in their valence shell, similar to the noble gas electron configuration. This rule helps to explain the driving forces behind the formation of chemical bonds.

For example, the magnesium ion Mg²⁺ achieves a stable octet by losing two electrons, mirroring the electron configuration of neon (Ne), a noble gas. Similarly, a neutrally charged fluorine atom will gain an electron to achieve a full octet, becoming F⁻ with an electron configuration identical to that of neon. Consequently, both Mg²⁺ and F⁻ ions have lower reactivity when compared to their neutral atoms because they have satisfied the octet rule, attaining electron configuration stability.

This rule does not apply to all elements, especially those beyond the second period of the periodic table which can have more than eight electrons in their valence shells. Nevertheless, it remains a valuable concept for understanding the behavior of many elements, particularly in main group chemistry.