Question

Refer to the periodic table and write the predicted electron configuration for each of the following negative ions using core notation: (a) \(\mathrm{F}^{-}\) (b) \(S^{2-}\) (c) \(\mathrm{N}^{3-}\) (d) \(\mathrm{I}^{3-}\)

Short answer

(a) \([\text{Ne}]\), (b) \([\text{Ar}]\), (c) \([\text{Ne}]\), (d) \([\text{Xe}]\) after adjustments.

Step-by-step solution

Understanding F^-

The atomic number of fluorine (F) is 9, meaning a neutral F atom has 9 electrons. The electron configuration of F is \(1s^2 2s^2 2p^5\). For \(\mathrm{F}^-\), it gains one electron to have 10 electrons. This makes its configuration \(1s^2 2s^2 2p^6\), which is the same as neon (Ne), so using core notation: \(\text{[Ne]}\).

Understanding S^2-

Sulfur (S) has an atomic number of 16, meaning 16 electrons for a neutral atom. The electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^4\). Adding 2 electrons for \(S^{2-}\) gives \(1s^2 2s^2 2p^6 3s^2 3p^6\), which matches argon (Ar), so using core notation: \(\text{[Ar]}\).

Understanding N^3-

The atomic number of nitrogen (N) is 7, so a neutral N atom has 7 electrons. The configuration is \(1s^2 2s^2 2p^3\). Adding 3 electrons for \(\mathrm{N}^{3-}\) yields \(1s^2 2s^2 2p^6\), the same as neon (Ne), so using core notation: \(\text{[Ne]}\).

Understanding I^3-

Iodine (I) has an atomic number of 53, thus 53 electrons normally. Its electron configuration is \([Kr] 4d^{10} 5s^2 5p^5\). For \(\mathrm{I}^{3-}\), it gains 3 electrons, so it becomes \([Kr] 4d^{10} 5s^2 5p^6 6s^2 5d^{10}\), which exceeds the next inert gas; however, in post-transition ion evaluation, you would stop where the configuration is normally saturated for 5p orbitals, here \([Xe]\).

Key concepts

Periodic Table

The periodic table is a powerful tool for understanding the arrangement of electrons in an atom. Each element in the periodic table is arranged based on its atomic number, which is the number of protons in its nucleus. This atomic number also tells you how many electrons a neutral atom of the element has. Elements are ordered sequentially across periods (rows) and within groups (columns) based on similar electron configurations and chemical properties. This arrangement allows us to predict how atoms will react and combine with other atoms. Inner electrons are referred to as core electrons, which are not directly involved in chemical bonding, while the outermost electrons, called valence electrons, are crucial in determining an element's reactivity. By understanding an element's position on the periodic table, you can determine its electron configuration and use this information to solve problems like predicting the electron configuration of ions.

Negative Ions

Negative ions, or anions, are formed when a neutral atom gains one or more electrons. The added electrons lead to an increase in the net negative charge of the atom, resulting in an ion with a negative charge. These ions are significant in many chemical reactions and biological processes. When forming negative ions, atoms typically gain enough electrons to reach the electron configuration of the nearest noble gas because these configurations are energetically stable. This principle is crucial for understanding why certain elements form particular types of ions. For example, fluorine (F) gains one electron to form \(\mathrm{F}^-\), achieving the electron configuration of neon (Ne), which is a noble gas. Studying how negative ions form helps us understand aspects of chemistry such as ionic bonding, where metals (which tend to lose electrons) bond with nonmetals (which tend to gain electrons).

Core Notation

Core notation is a shorthand method to express the electron configuration of an atom. It uses the electronic structure of the last preceding noble gas as a reference or 'core' to simplify the configuration notation. For example, the core notation for fluorine ion \((\mathrm{F}^-)\) starts with the configuration of neon (Ne), which is \([Ne]\). Then, any additional electrons specific to fluorine are added. This simplifies communication and makes it easier to visualize electron sharing or transfer during chemical reactions. By using core notation, chemists can quickly write out or mentally process the electronic structure of complex ions or atoms without having to write out the entire configuration each time, simplifying tasks such as predicting the behavior of elements during chemical reactions.