Problem 93 - Chemistry The Science in Context

Question

What are the electron configurations of \(\mathrm{Li}, \mathrm{Li}^{+}, \mathrm{Ca}, \mathrm{F}^{-}\) \(\mathrm{Na}^{+}, \mathrm{Mg}^{2+},\) and \(\mathrm{Al}^{3+} ?\)

Step-by-Step Solution

Answer

Based on the step-by-step solution above, the electron configurations for the given atoms and ions are: 1. Li: 1s²2s¹ 2. Li+: 1s² 3. Ca: 1s²2s²2p⁶3s²3p⁶4s²3d⁰ 4. F-: 1s²2s²2p⁶ 5. Na+: 1s²2s²2p⁶ 6. Mg2+: 1s²2s²2p⁶ 7. Al3+: 1s²2s²2p⁶ Provide the corresponding electron configuration for each of the given atoms and ions.

Step 1: Determine the atomic numbers of the elements

To find the electron configurations for each atom and ion, we need to first determine the atomic numbers (number of protons) for the given elements. Using the periodic table, we can find the atomic numbers for Li (Lithium), Ca (Calcium), F (Fluorine), Na (Sodium), Mg (Magnesium), and Al (Aluminum). Li: Atomic Number = 3 Ca: Atomic Number = 20 F: Atomic Number = 9 Na: Atomic Number = 11 Mg: Atomic Number = 12 Al: Atomic Number = 13

Step 2: Find electrons for the given ions

Next, we need to determine the number of electrons for each ion. For neutral atoms, the number of electrons is the same as the atomic number. For ions, we adjust the number of electrons based on the charge of the ion. Li: 3 electrons Li+: 3 - 1 = 2 electrons Ca: 20 electrons F-: 9 + 1 = 10 electrons Na+: 11 - 1 = 10 electrons Mg2+: 12 - 2 = 10 electrons Al3+: 13 - 3 = 10 electrons

Step 3: Write the electron configurations based on Aufbau principle, Hund's rule, and Pauli Exclusion Principle

Now, we can find the electron configurations for each atom/ion: Li (3 electrons): 1s²2s¹ Li+ (2 electrons): 1s² Ca (20 electrons): 1s²2s²2p⁶3s²3p⁶4s²3d⁰ F- (10 electrons): 1s²2s²2p⁶ Na+ (10 electrons): 1s²2s²2p⁶ Mg2+ (10 electrons): 1s²2s²2p⁶ Al3+ (10 electrons): 1s²2s²2p⁶ So, the electron configurations for the given atoms/ions are: Li: 1s²2s¹ Li+: 1s² Ca: 1s²2s²2p⁶3s²3p⁶4s²3d⁰ F-: 1s²2s²2p⁶ Na+: 1s²2s²2p⁶ Mg2+: 1s²2s²2p⁶ Al3+: 1s²2s²2p⁶

Key Concepts

Atomic Number

The atomic number of an element is a fundamental property that tells us how many protons are in the nucleus of its atoms. It is unique for each element and can be found on the periodic table. In neutral atoms, the atomic number is equal to the number of electrons, defining its electron configuration. Knowing the atomic number is crucial when determining the basic electron setup of any atom.
For instance:

• Lithium (Li) has an atomic number of 3, so it contains 3 protons and, in its neutral state, 3 electrons.
• Calcium (Ca) has an atomic number of 20, with 20 protons and 20 electrons in its neutral form.
• Fluorine (F) holds an atomic number of 9, so it has 9 protons and 9 electrons if neutral.
• Sodium (Na), Magnesium (Mg), and Aluminum (Al) have respective atomic numbers of 11, 12, and 13.

A clear understanding of atomic numbers aids in further electron configuration calculations, particularly when ions are formed.

Ions

Ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net charge. This process changes the electron configuration from that of a neutral atom, affecting the chemical properties. Ions are crucial in chemical reactions and biological processes.
For example:

• A lithium ion (Li⁺) has lost one electron compared to its neutral state, leaving it with only 2 electrons.
• A fluoride ion (F⁻), however, has gained an electron, resulting in 10 electrons total, like a neon atom.
• Sodium and magnesium form Na⁺ and Mg²⁺ ions by losing electrons, achieving stable electron configurations similar to Ne.

Understanding ions helps explain why different substances behave the way they do in chemical reactions and how atomic structure relates to stability.

Aufbau Principle

The Aufbau principle is a rule used to systematically build electron configurations in atoms. It states that electrons fill atomic orbitals of the lowest available energy level before occupying higher levels. This helps in determining how electrons are distributed among the orbitals.
According to the Aufbau principle:

• Electrons first fill the 1s orbital before moving to the 2s, then to the 2p, and so on.
• For instance, calcium (Ca) with 20 electrons, would fill orbitals in the order: 1s², 2s², 2p⁶, 3s², 3p⁶, then 4s².
• For ions, the same principle applies after adjusting the total number of electrons as per the ion's charge.

This principle works alongside Hund's rule and the Pauli Exclusion Principle to define how electrons arrange themselves in an atom's orbitals, culminating in a clear picture of their configurations.