Problem 179 - Introductory Chemistry Atoms First

Question

Write the full ground-state electron configuration for \(\mathrm{Ca}^{2+}, \mathrm{S}^{2-}, \mathrm{Ar}, \mathrm{K}^{+}\)

Step-by-Step Solution

Answer

The full ground-state electron configurations for the given ions/elements are: - \(\mathrm{Ca}^{2+}\): 1s², 2s², 2p⁶, 3s², 3p⁶ - \(\mathrm{S}^{2-}\): 1s², 2s², 2p⁶, 3s², 3p⁶ - \(\mathrm{Ar}\): 1s², 2s², 2p⁶, 3s², 3p⁶ - \(\mathrm{K}^{+}\): 1s², 2s², 2p⁶, 3s², 3p⁶

Step 1: Identify the Atom's Position in the Periodic Table

To identify each atom's position in the periodic table, use a periodic table to look for the atomic number, which represents the number of protons in a neutral atom. Since the ions/elements given are \(\mathrm{Ca}^{2+}, \mathrm{S}^{2-}, \mathrm{Ar}, \mathrm{K}^{+}\), we can determine their atomic numbers as follows: -Calcium (Ca): atomic number 20 -Sulfur (S): atomic number 16 -Argon (Ar): atomic number 18 -Potassium (K): atomic number 19

Step 2: Write the Electron Configuration Using Subshells and Their Occupancies

Now, we can write the electron configuration for each ion/element using the identified atomic numbers and accounting for the changes in electron numbers due to the charges on the ions. The electron configuration is written using subshells (s, p, d, f) and their occupancies. 1. \(\mathrm{Ca}^{2+}\): 10 less 2 electrons due to the charge, so 18 electrons Electron configuration: 1s², 2s², 2p⁶, 3s², 3p⁶ 2. \(\mathrm{S}^{2-}\): 16 plus 2 electrons due to the charge, so 18 electrons Electron configuration: 1s², 2s², 2p⁶, 3s², 3p⁶ 3. \(\mathrm{Ar}\): 18 electrons (neutral atom) Electron configuration: 1s², 2s², 2p⁶, 3s², 3p⁶ 4. \(\mathrm{K}^{+}\): 19 less 1 electron due to the charge, so 18 electrons Electron configuration: 1s², 2s², 2p⁶, 3s², 3p⁶ So, the full ground-state electron configurations for the given ions/elements are: - \(\mathrm{Ca}^{2+}\): 1s², 2s², 2p⁶, 3s², 3p⁶ - \(\mathrm{S}^{2-}\): 1s², 2s², 2p⁶, 3s², 3p⁶ - \(\mathrm{Ar}\): 1s², 2s², 2p⁶, 3s², 3p⁶ - \(\mathrm{K}^{+}\): 1s², 2s², 2p⁶, 3s², 3p⁶

Key Concepts

Ions

Ions are atoms or molecules that have gained or lost one or more electrons, giving them a net electrical charge. When an atom gains electrons, it becomes negatively charged and is called an anion. Conversely, when it loses electrons, it becomes positively charged and is known as a cation. In the exercise, we see examples of both:

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