Problem 84 - Introductory Chemistry Atoms First

Question

Write the electron configuration for the following elements without using the noble gas abbreviated form (use the periodic table to assist you). (a) \(\bar{B}\) (b) \(\mathrm{Sc}\) (c) \(\mathrm{Co}\) (d) Se (e) \(\mathrm{Ru}\)

Step-by-Step Solution

Answer

(a) B: 1s² 2s² 2p¹ (b) Sc: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹ (c) Co: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷ (d) Se: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴ (e) Ru: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁶

Step 1: Determine the atomic numbers of the elements

Using the periodic table, find the atomic numbers of the given elements: (a) B - Boron has atomic number 5. (b) Sc - Scandium has atomic number 21. (c) Co - Cobalt has atomic number 27. (d) Se - Selenium has atomic number 34. (e) Ru - Ruthenium has atomic number 44.

Step 2: Electron configuration for B (Boron)

Since Boron has an atomic number 5, it has 5 electrons. We must distribute these electrons in orbitals: 1s² 2s² 2p¹

Step 3: Electron configuration for Sc (Scandium)

Scandium has an atomic number 21, so it has 21 electrons. Distribute these electrons in orbitals: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹

Step 4: Electron configuration for Co (Cobalt)

Cobalt has an atomic number 27, so it has 27 electrons. Distribute these electrons in orbitals: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷

Step 5: Electron configuration for Se (Selenium)

Selenium has an atomic number 34, so it has 34 electrons. Distribute these electrons in orbitals: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴

Step 6: Electron configuration for Ru (Ruthenium)

Ruthenium has an atomic number 44, so it has 44 electrons. Distribute these electrons in orbitals: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁶ Now, we have found the electron configuration of the given elements without using the noble gas abbreviation.

Key Concepts

Atomic Number

The atomic number is a fundamental concept in chemistry and physics. It is defined as the number of protons found in the nucleus of an atom. This number is unique for each element and determines its identity. For example, boron has an atomic number of 5, meaning it contains 5 protons in its nucleus. Consequently, the atomic number also indicates the number of electrons surrounding the nucleus in a neutral atom.
Understanding the atomic number is crucial when determining electron configurations because it tells us exactly how many electrons need to be placed in orbitals. The electron configuration reflects the distribution of these electrons across various energy levels and sublevels within the atom.

• Atomic number = Number of protons = Number of electrons (in a neutral atom)
• Unique identifier for each element
• Determines electron distribution

Orbital Distribution

Orbital distribution is how electrons are spread out in an atom's orbitals. Orbitals are regions around the nucleus where electrons are likely found, and they come in different shapes and sizes. Key orbital types include s, p, d, and f orbitals.
For example, in the electron configuration for boron, which has an atomic number of 5, electrons fill the orbitals as follows:

• 1s²: First fill the 1s orbital with 2 electrons.
• 2s²: Next, fill the 2s orbital with 2 electrons.
• 2p¹: Finally, place the remaining electron in the 2p orbital.

Filling follows the Aufbau principle, which prioritizes filling lower-energy orbitals first. Electrons fill orbitals in order of increasing energy. Other principles like Hund's Rule, stating that every orbital in a subshell should be occupied singly before being doubly occupied, are also at play.

Bohr Model

The Bohr Model is one of the early and significant models in atomic theory developed by Niels Bohr. Although considered somewhat outdated, it provides a simple visualization of atomic structure, especially helpful for beginners. It depicts electrons moving in circular orbits around a positively charged nucleus, somewhat like planets orbiting the sun. In this model:

• Electrons orbit the nucleus in discrete paths or energy levels.
• Each orbit represents a different energy level, which is quantized.
• Electrons can jump between levels by absorbing or emitting energy.

Though the Bohr Model introduces quantization, it does not accurately describe more complex atoms, as it assumes a definitive path for electrons. Nevertheless, it laid the groundwork, later refined by quantum mechanics, for understanding atomic theory.

Quantum Mechanics

Quantum mechanics revolutionized our understanding of atomic structure. It describes electrons not as particles in fixed orbits, but as wave-like entities. This introduces the concept of electron clouds or probability distributions around the nucleus. In quantum mechanics, electron behavior is described by the Schrödinger equation, which defines a wave function for each electron. Instead of definite paths, electrons inhabit orbitals, which are probability zones where an electron is likely to be found.
Principles such as the Heisenberg Uncertainty Principle further clarify that one cannot exactly determine both the position and momentum of an electron at given point in time.

• Considers electrons as wave-like
• Electrons exist in probability distributions, not fixed paths
• Foundation for modern atomic models

Quantum mechanics provides a much more comprehensive framework for understanding the behavior and arrangement of electrons in atoms than models like Bohr's.