Question

For each of the orbital diagrams given, write out the corresponding electron configurations. (a) \(\mathrm{O}\) (b) \(\mathrm{Ca}\) (c) \(\mathrm{Ar}\) (d) \(\mathrm{Br}\) (e) \(\mathrm{Fe}\)

Short answer

The electron configurations are (a) Oxygen: 1s² 2s² 2p⁴, (b) Calcium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s², (c) Argon: 1s² 2s² 2p⁶ 3s² 3p⁶, (d) Bromine: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵, (e) Iron: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s².

Step-by-step solution

Determine Electron Configuration for Oxygen (O)

Oxygen has an atomic number of 8, which means it has 8 electrons. The electron configuration is written based on the order of filling of orbitals according to the Aufbau principle. The orbitals are filled in the following order: 1s, 2s, 2p. So, oxygen's electron configuration is 1s² 2s² 2p⁴.

Determine Electron Configuration for Calcium (Ca)

Calcium has an atomic number of 20, which means it has 20 electrons. Following the order of filling: 1s, 2s, 2p, 3s, 3p, 4s, calcium fills up to 4s. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².

Determine Electron Configuration for Argon (Ar)

Argon has an atomic number of 18, indicating 18 electrons. The orbitals are filled up to 3p level, giving the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶.

Determine Electron Configuration for Bromine (Br)

Bromine has an atomic number of 35, with 35 electrons. The electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵, as the orbitals are filled up to the 4p level.

Determine Electron Configuration for Iron (Fe)

Iron, with an atomic number of 26, will have 26 electrons. The electron configuration follows as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². Note that the 4s orbital is filled before starting to fill the 3d orbital.

Key concepts

Aufbau Principle

Understanding the Aufbau principle is key to knowing how electrons arrange themselves in an atom. The word 'Aufbau' is German for 'building up', reflecting the idea that electrons fill up orbitals in a way that builds up the atom's electron configuration from the ground up. According to this principle, electrons occupy the lowest energy orbital that can receive them. It's a fundamental guideline for predicting the electron configurations of elements.

Imagine you are organizing books on a shelf. You'd likely start by filling the bottom shelf before moving up to the next one. Similarly, the Aufbau principle tells us to start at the lowest energy level and work our way up. It helps explain why the electron configuration for Oxygen starts with 1s² before moving to 2s² and finally to 2p⁴. The numbering represents energy levels, where '1s' is the lowest energy orbital available to Oxygen's electrons.

Orbital Diagrams

Orbital diagrams visualize how electrons populate an atom's orbitals. They are pictorial descriptions that use arrows to represent electrons. Each arrow in an orbital stands for one electron, with the direction of the arrow (up or down) indicating the electron's spin. A crucial rule here is Hund's rule, which states that electrons will fill orbits singly first, with parallel spins, before pairing up.

When writing electron configurations, orbital diagrams act as a helpful tool to ensure that electron spin and distribution across the orbitals are correctly accounted for. This is important in the case of Iron (Fe), where after filling the 3p orbitals, electrons start to fill the 3d and 4s orbitals. An orbital diagram helps visualize this unique arrangement and ensures students don't miss the subtle differences in electron distribution even within the same principal energy level.

Atomic Number

The atomic number is a fundamental characteristic of an element and is central to the identity of an atom. It can tell you a lot about an element's properties, including its position in the periodic table and the type of chemical reactions it may undergo. The atomic number represents the number of protons in an atom's nucleus and by extension, because atoms are electrically neutral, it also indicates the number of electrons in a neutral atom.

The atomic number is so important that it determines the order in which the periodic table is arranged. For Calcium (Ca), the atomic number is 20 - meaning it has 20 protons and 20 electrons. This atomic number guides us in using the Aufbau principle and Hund's rule to figure out the electron configuration and orbital arrangement for Calcium. The initial steps in solving electron configurations always emphasize finding out the atomic number, because from there, everything else follows.