Problem 49 - Chemistry An Atoms First Approach

Question

Write electron configurations for a. the cations \(\mathrm{Mg}^{2+}, \mathrm{K}^{+},\) and \(\mathrm{Al}^{3+}\) b. the anions \(\mathrm{N}^{3-}, \mathrm{O}^{2-}, \mathrm{F}^{-},\) and \(\mathrm{Te}^{2-}\)

Step-by-Step Solution

Answer

a. Cations: \(\mathrm{Mg}^{2+}\): [Ne] \(\mathrm{K}^{+}\): [Ar] \(\mathrm{Al}^{3+}\): [Ne] b. Anions: \(\mathrm{N}^{3-}\): [Ne] \(\mathrm{O}^{2-}\): [Ne] \(\mathrm{F}^{-}\): [Ne] \(\mathrm{Te}^{2-}\): [Kr]5s²4d¹⁰5p⁶

Step 1: Identify the atomic numbers of the elements

Consult the periodic table to find the atomic numbers of the given elements. Mg: atomic number 12 K: atomic number 19 Al: atomic number 13 N: atomic number 7 O: atomic number 8 F: atomic number 9 Te: atomic number 52

Step 2: Determine the number of electrons for each ion

Based on the atomic numbers and the charges in the exercise, we can now determine the number of electrons for each ion: \(\mathrm{Mg}^{2+}\): 12 - 2 = 10 electrons \(\mathrm{K}^{+}\): 19 - 1 = 18 electrons \(\mathrm{Al}^{3+}\): 13 - 3 = 10 electrons \(\mathrm{N}^{3-}\): 7 + 3 = 10 electrons \(\mathrm{O}^{2-}\): 8 + 2 = 10 electrons \(\mathrm{F}^{-}\): 9 + 1 = 10 electrons \(\mathrm{Te}^{2-}\): 52 + 2 = 54 electrons

Step 3: Write the electron configurations

Now that we know the number of electrons for each ion, we can write their electron configurations: a. Cations: \(\mathrm{Mg}^{2+}\): [Ne] \(\mathrm{K}^{+}\): [Ar] \(\mathrm{Al}^{3+}\): [Ne] b. Anions: \(\mathrm{N}^{3-}\): [Ne] \(\mathrm{O}^{2-}\): [Ne] \(\mathrm{F}^{-}\): [Ne] \(\mathrm{Te}^{2-}\): [Kr]5s²4d¹⁰5p⁶ Note that we used noble gas shorthand configurations for ease of writing.

Key Concepts

Cation and Anion Charge

Cations and anions are ions with positive and negative charges, respectively. A cation is formed when an atom loses one or more electrons, resulting in a net positive charge. Conversely, an anion is created when an atom gains electrons, leading to a net negative charge.

The charge on an ion is significant because it determines how electrons are added or removed to reach the electron configuration of the ion. In the case of cations like \(\mathrm{Mg}^{2+}\), \(\mathrm{K}^{+}\), and \(\mathrm{Al}^{3+}\), electrons are removed from the neutral element's electron configuration. For anions such as \(\mathrm{N}^{3-}\), \(\mathrm{O}^{2-}\), \(\mathrm{F}^{-}\), and \(\mathrm{Te}^{2-}\), extra electrons are added.

This concept is crucial to understand as it affects the chemical reactivity and bonding behavior of the elements.

Periodic Table

The periodic table is a systematic arrangement of elements based on their atomic numbers, electron configurations, and recurring chemical properties. Elements are ordered in rows called periods and columns known as groups or families.

Understanding the periodic table is vital for predicting an element's behavior and its interaction with other elements. For instance, the group number can indicate the number of valence electrons in an atom's outer shell, and an element's period number correlates to the number of electron shells.

Atomic Number

The atomic number of an element is the number of protons found in the nucleus of an atom of that element. It determines the element's identity and is denoted by the symbol 'Z.' In the periodic table, elements are arranged in the order of increasing atomic numbers.

The atomic number is also essential for writing electron configurations, as it equals the number of electrons in a neutrally charged atom. For example, magnesium has an atomic number of 12, indicating it has 12 protons and, in its neutral state, 12 electrons.

Electron Configuration Notation

Electron configuration notation describes the arrangement of electrons in an atom or ion using specific rules. In this notation, the principal energy level (n) is followed by the letter of the sublevel (s, p, d, f), which is then followed by a superscript indicating the number of electrons in that sublevel.

For example, for magnesium ion \(\mathrm{Mg}^{2+}\) with 10 electrons, its electron configuration would stop at the neon shell since two electrons are lost, resulting in the notation [Ne]. Understanding these notations enables us to visualize how electrons populate an atom and predict its chemical behavior.

Noble Gas Shorthand

Noble gas shorthand is a simplified way of expressing electron configurations. It uses the electron configuration of the nearest noble gas that precedes the element in the periodic table, followed by the remainder electron configuration.

This shorthand is used to avoid writing long, full electron configurations for elements with many electrons. For instance, the shorthand for tellurium anion \(\mathrm{Te}^{2-}\) is [Kr]5s²4d¹⁰5p⁶, where [Kr] represents krypton's full electron configuration, which precedes tellurium in the periodic table. This approach makes it easier to identify electron configurations, especially for heavy elements.