Electron Configuration: Orbital, Noble-Gas & Electron-Configuration Notation

Instructor: Elizabeth (Nikki) Wyman

Nikki has a master's degree in teaching chemistry and has taught high school chemistry, biology and astronomy.

Discover the complex ways that electrons are organized within an atom. Learn two ways to write electron configurations to show how electrons are organized. Then, test your new knowledge with a quiz.

Electron Orbitals

Electrons are the small, negatively charged particles that buzz around the nucleus of an atom like a swarm of bees. Though electrons are small, discreet particles like bees, their behavior is way more bizarre!

Whereas bees might swarm around the hive however they want, electrons are confined to certain areas around the nucleus based how much energy they have. We can surmise where an electron is likely to be, but it's hard to pinpoint the exact location. To make things even more strange, electrons appear to be everywhere at once, just like the blades of a fan.

A model representing where electrons are likely to be in a helium atom. Electrons are more likely to be found in darker areas.
Electron cloud model

Electrons are principally organized into energy levels based on how much energy they have and how close they are to the nucleus. The closest energy level to the nucleus is simply referred to as the first energy level, followed by the second energy level, then the third energy level and so on. Energy levels are often represented by the letter n and a number. So the first energy level might be referred to as n =1, the second as n = 2.

Each energy level is made up of one or more orbitals. Orbitals are the specific shapes that electrons are likely to inhabit. In total, there are four different kinds of orbitals: s, p, d and f.

Every energy level contains one spherically shaped s orbital. In fact, the first energy level is comprised only of an s orbital. The s orbital is the least energetic orbital of any given energy level and it can contain a maximum of two electrons.

Image of s and p orbitals

Energy levels two and above contain a p orbital. This orbital is made up of three intersecting hour glass shapes. In total, each p orbital can contain up to six electrons. This orbital houses slightly more energetic electrons than the s orbital, but not as much as the d orbital!

The d orbital is a set of five goofy shapes that collectively can contain up to 10 electrons. d orbitals are only present in energy levels three and above.

These five shapes comprise a d orbital.
Image of d orbitals

Lastly, we have the f orbital. This orbital consists of seven wacky shapes capable of holding up to fourteen electrons. The f orbital occurs in energy levels four and above.

We can summarize the types of orbitals present in each energy level in the table below:

Energy Level Orbitals Present Maximum Electron Capacity
1 s 2
2 s, p 8
3 s, p, d 18
4 s, p, d, f 32

Electrons in Orbitals

In their neutral state, every element contains the same number of electrons as protons (the atomic number). For example carbon has an atomic number of 6 and therefore 6 protons and 6 electrons.

Electrons fill up the lowest energy levels first. Within each energy level the lowest energy orbitals are filled first. It's a bit like parking spaces close to the entrance of a building; the spaces closest to the entrance fill first. As more cars arrive, the vacant spots get farther and farther away.

In the case of carbon, the parking spots closest to the nucleus get filled first: two electrons go in 1s, two into 2s and two into 2p. The p orbital is only partially filled and that is totally okay!

Below is a schematic diagram of how orbitals and energy levels are organized. This might help you visualize the energies of the electron parking spaces. Each parking space can hold two electrons.

Representation of orbitals

Note that though some orbitals are lower in energy than orbitals in a higher energy level (4s is lower in energy than 3d). Regardless, the lower energy orbital will always fill first. This is goofy and obnoxious, but we'll go over some mnemonic devices for remembering the order.

Electron Configuration Notation

The organization of electrons within energy levels and orbitals is called the electron configuration. Because every element has a unique number of electrons, every element has a unique electron configuration.

To write the electron configuration, we list all of the orbitals occupied by electrons in order of increasing energy. Each orbital must include three pieces of information: the energy level, the shape of the orbital and the number of electrons inside. The energy level is simply represented by the energy level number (1, 2...n), the orbital shape is represented by the appropriate letter (s, p, d or f) and the number of electrons are written as a superscript immediately following the orbital shape (1-14).

For carbon we would write: 1s^2, 2s^2, 2p^2.

All the superscripts added together should equal the atomic number.

There are a few ways to remember orbital order when writing electron configurations.

  • You can memorize it.
  • You can refer to the schematic diagram above and manually fill in electrons, then write out each orbital in order of increasing energy.
  • You can use the diagram below.

Device for filling in orbitals

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