Question

Write the predicted electron configuration for each of the following elements: (a) boron (b) argon (c) manganese (d) nickel

Short answer

(a) 1s² 2s² 2p¹; (b) 1s² 2s² 2p⁶ 3s² 3p⁶; (c) 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵; (d) 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸.

Step-by-step solution

Understand Electron Configuration

Electron configuration is a representation of the arrangement of electrons distributed among the atomic orbitals of an atom. Electrons fill orbitals starting from the lowest energy level to higher levels, following the Aufbau principle, Pauli-exclusion principle, and Hund's rule.

Electron Configuration Notation

The electron configuration is written using numbers, letters, and superscripts. The numbers represent the energy level, the letters (s, p, d, f) represent the type of orbital, and the superscripts represent the number of electrons in those orbitals.

Determine Boron's Configuration (a)

The atomic number of boron is 5, which means it has 5 electrons. Start filling from the lowest energy orbitals: 1s², 2s², and then 2p¹. So, the electron configuration for boron is 1s² 2s² 2p¹.

Determine Argon's Configuration (b)

The atomic number for argon is 18. Fill the orbitals as follows: 1s² 2s² 2p⁶ 3s² 3p⁶. Therefore, argon's electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶.

Determine Manganese's Configuration (c)

Manganese has an atomic number of 25. Fill the orbitals up to 3d by remembering that the 4s orbital fills before the 3d orbital: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵. Thus, manganese's electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵.

Determine Nickel's Configuration (d)

Nickel has an atomic number of 28. Fill orbitals similarly to manganese but adding more electrons to the 3d orbital: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸. Therefore, nickel's electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸.

Key concepts

Aufbau principle

The Aufbau principle is the cornerstone for predicting the electron configurations of atoms. It suggests that electrons occupy the lowest energy orbital available. This means that electrons will fill up atomic orbitals, starting from the lowest possible energy level, progressively moving to higher energies.

By following the Aufbau pattern, electrons will first fill the 1s orbital, the lowest on the energy scale, before moving on to 2s, 2p, and so on. The term *Aufbau* comes from a German word that means "building up," which reflects this step-by-step filling process.

• Electrons fill orbitals in order of increasing energy.
• For an atom like boron with five electrons, the filling order would be 1s², 2s², and then 2p¹.

Understanding this principle helps predict the electron configuration of any element, showing the simplest path of electrons as they build up around the nucleus.

Pauli-exclusion principle

The Pauli-exclusion principle sheds light on why electrons within an atom have unique placements. According to this principle, no two electrons can have the same set of four quantum numbers. In simple terms, it means an atomic orbital can hold a maximum of two electrons, and these electrons must have opposite spins.

This principle ensures that electrons are distributed uniquely, avoiding duplication in configuration. When filling orbitals, each electron can be seen as having a unique "address," defined by its energy level, sublevel, orbital, and spin.

• An orbital can accommodate two electrons, each with a different spin.
• Think of it like a twin bed that can only fit two people, one sleeping face up and the other face down.

This principle is essential to understand why electron configurations work as they do, contributing to the atom's overall stability.

Hund's rule

Habits of electrons when occupying orbitals are described by Hund's rule. This principle states that electrons will fill orbitals of a sublevel singly before pairing up. Like riders preferring their own row of seats before sitting with others, electrons aim for unoccupied orbitals first.

By filling orbitals singly, electrons minimize repulsion, maintaining lower energy configurations and maximizing stability.

• Electrons will fill each p, d, or f orbital singly before pairing up.
• In the case of the 2p sublevel of boron, one electron will occupy a different orbital before any pairing occurs.

Following Hund's rule helps predict the configuration of electrons, especially for atoms with partially filled sublevels.

Atomic orbitals

Atomic orbitals describe regions around a nucleus where electrons are most likely found. They come in various shapes and sizes, primarily identified as s, p, d, and f orbitals.

The s orbitals are spherical, p orbitals have a dumbbell shape, while d and f orbitals have more complex forms. Electrons in atoms inhabit these orbitals, according to the principles we've discussed.

• s orbitals can hold up to 2 electrons.
• p orbitals can hold up to 6 electrons, distributed across three p orbitals.
• d and f orbitals can hold 10 and 14 electrons, respectively.

Understanding atomic orbitals is crucial for visualizing how elements keep their electrons arranged.

Electron notation

Electron notation is a shorthand description outlining how electrons fill the atomic orbitals. This notation uses numbers and letters to represent the energy levels and types of orbital that electrons occupy.

In electron notation:

• The number indicates the principal energy level (like 1, 2, 3...).
• The letter identifies the orbital type ( s, p, d, f).
• The superscript shows the number of electrons in that orbital, such as 2p⁶ indicating a full p sublevel.

For example, argon's electron configuration is expressed as 1s² 2s² 2p⁶ 3s² 3p⁶, showing each filled energy level and orbital type in sequence. Electron notation simplifies understanding an atom's electronic structure.