Orbital Diagrams — Overview & Examples

Orbital Diagrams

• Orbital diagrams help visualize which orbitals the electrons in an atom are

The Basics of Orbital Diagrams

• There are different types of orbitals, that all have different energy levels. These orbitals are filled with electrons (the amount of electrons depends on which element you are looking at).

• S orbitals make up 1 box, and contain a max of 2 electrons
• P orbitals make up 3 boxes, and contain a max of 6 electrons total (2 in each box)
• D orbitals make up 5 boxes, and contain a max of 10 electrons (2 in each box)
• F orbitals make up 7 boxes, and contain a max of 14 electrons (2 in each box)

Here is a cheat sheet to remember the order of the orbital diagrams!

Electron Configuration vs Orbital Diagrams

• The electron configuration is a written out version of the orbital diagram!

The Three Rules for Creating Orbital Diagrams

1. The lowest energy orbitals are filled before the higher energy orbitals (Aufbau Principle)
2. Each orbital gets one electron first, before adding the second electron to the orbital (Hund’s Rule)
3. Only 2 electrons, of opposite spins, can occupy each orbital (Pauli Exclusion Principle)

Practice Problem Walkthrough

What is the orbital diagram for Sulfur?

1. Look at the periodic table to see how many electrons sulfur has

• In this case, sulfur has 16 electrons that need to be placed into orbitals

1. Looking at our cheat sheet, draw the orbitals one at a time, adding electrons as you go, until you reach a total of 16 electrons

(Video) Orbital Diagrams and Electron Configuration - Basic Introduction - Chemistry Practice Problems

By: The Organic Chemistry Tutor

This video covers how to create and fill orbital diagrams.

The first example looks at a nitrogen atom. The diagram is created using the electron configuration. Degenerate orbitals and how to fill them is discussed. The electron pairing is discussed in terms of paramagnetic (unpaired electrons) and diamagnetic (paired electrons).

The next example goes over magnesium. This diagram is filled by knowing the number of electrons and filling from the lowest orbitals first then the high energy levels.

The third part of the video allows the watcher to practice phosphorus on their own. The presenter then goes over the example.

Next, the video goes over an ions with charges $S^{2-}$, $Al^{3+}$, and $Co^{2+}$. The video discusses that transition metals can be tricky and goes over the variation with the cobalt ion.

We've been studying quantum mechanics. In the quantum mechanical model, electrons reside in orbitals. We learned that orbitals are described by quantum numbers. We've also learned how to write electron configurations for neutral atoms and ions. But, an electron configuration does not give us the full picture. Electron configurations do not show orbital energies or electron pairing. That's the first and fourth quantum numbers. To show energies and electron pairing we use an orbital diagram. An orbital diagram is a pictorial representation of how electrons fill atomic orbitals.

Rules for How Electrons fill Orbitals

Remember that we have three rules that determine how electrons fill atomic orbitals.

1. The Aufbau Principle: Electrons fill the lowest energy orbitals first.
2. Hund's Rule: Atomic orbitals maximize the number of electrons with the same spin.
3. The Pauli Exclusion Principle: Electrons will pair with opposite spins.

Steps for Drawing an Orbital Diagram

1. Draw a long vertical arrow that points upward. Label the arrow energy. The arrow shows a qualitative representation of increasing orbital energy.
2. Write out the electron configuration to determine which orbitals are filled. Remember, we can use the periodic table to help us. A neutral atom has an equal number of electrons and protons. So, the total number of electrons equals our atomic number. Also, remember that the periodic table is divided into blocks based on orbitals. So, the alkali and alkaline earth metals are the s-block. The non-metals, metalloids, and noble gases are the p-block. The transition metals are the d-block. The lanthanides and actinides are the f-block.
3. Along the right side of the energy arrow, write each electron shell that is being filled. The 1s electron shell is at the bottom of the arrow. As the electron shells increase in energy place them higher up the arrow. The valence electrons should be in the highest electron shells.
4. Next to each electron shell level, draw a box for each subshell. S-orbitals have one subshell. P-orbitals have three subshells. D-orbitals have five subshells. F-orbitals have seven subshells. The subshells all have equal energy. So, draw each box next to the others.
5. For each electron in a subshell, place an arrow in its box. An up arrow represents a spin-up electron. A down arrow represents a spin-down electron. We start with spin-up arrows. As the electrons pair, we add spin-down arrows.

A Few Things to Watch For

1. Because of Hund's Rule, you may have boxes with unpaired electrons. That's okay! Electrons prefer to be unpaired. Each box that has an unpaired electron should have an up arrow.
2. It is also okay to have some unpaired subshells and some paired subshells in the same energy level.
3. Remember that some of the transition metals, lanthanides, and actinides have unique electron configurations. For unique electron configurations, you have to adjust your orbital diagrams.