Electron Configurations

Lesson Plan - Get It!

Audio:

If you had a map, it would be a lot easier to find your way in a new city.

• What if you didn't have a map?

It would be very challenging to find your way around.

Elements on the periodic table are mapped based on the electrons found in the atom. This organization helps scientists and chemists communicate and compare elements. The map for each element is called the electron configuration. It shows where the electrons are found in the atom.

Surrounding an atomic nucleus are electron orbital sets. These are differently-shaped regions where electrons are frequently found.

Each orbital set can hold a different number of electrons based on the size and shape. The s orbital set is the smallest orbital and is found closest to the nucleus. It can hold two electrons because of the spherical shape.

The p orbital is larger, kind of like two identical balloons tied together in the middle. P orbital sets have three distinct orbitals, each able to hold two electrons, for a total of six electrons.

The d orbital set has more lobes, and can therefore hold more electrons. It is made of five orbitals, and able to hold ten electrons total.

There are f orbital sets, which are far larger in size and can hold up to 16 electrons. You won't be asked to identify or draw them, but it is helpful to know they exist!

Electron orbitals build in layers, with elements at the bottom of the periodic table having more levels of s orbitals.

Notice the numbers on the left-hand side of the image above. These provide the level location for each set of orbitals in an electron configuration. Higher level values mean the atom has many levels of electrons, each one farther from the nucleus.

The electron configuration for Na (sodium) is 1s²2s²2p⁶3s¹. The numbers at the front (1, 2, 2, 3) indicate the electron level. The letters (s, s, p, s) provide the type of orbital electrons are found in. The superscript values (2, 2, 6, 1) give the number of electrons found in that orbital on the electron level. So, sodium has two electrons in the s orbital on level one. It has two electrons in the s orbital on level two, and six electrons in the p orbital on level two.

• How many total electrons does sodium have on level two?

Eight.

Once an electron level has eight electrons, it is full. This is called the octet rule in chemistry. Atoms always want eight electrons in the outer level. Sodium does not have eight electrons in the outer level, so it will bond with other elements to satisfy the octet rule.

The electrons found in the outer layer of an atom are called valence electrons.

• How many valence electrons does sodium have?

Just one, meaning that it needs seven to be considered full. There is one exception to the octet rule, and that is in electron level one. Level one only needs two electrons, because the only orbital is s-shaped, meaning that it is small and only able to hold two electrons.

Look at oxygen (O). The electron configuration for oxygen is 1s²2s²2p⁴. Oxygen has two electrons in the first level.

• How many valence electrons does oxygen have in the outer level?

Add both sets of electrons located in level two, so six. Oxygen has six valence electrons.

The periodic table is organized according to the orbital shapes as shown in the image below:

^{By Sch0013r (Wikipedia) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons}

Now that you have seen how the periodic table is organized, look back at the electron configurations for sodium and oxygen. Notice how the level numbers line up with the orbital letters used in the configurations. Make a prediction for the electron configuration for fluorine (F):

Electron configurations are maps of the atom that help scientists understand where electrons are located. They rely on the levels of electron organization around the nucleus and are based on different shapes of orbitals that electrons are found inside. Atoms are constantly trying to achieve eight electrons in the outer layer, which is an important concept in chemical bonding.

Create a sketch that summarizes what you have learned before moving on.

In the Got It? section, you will watch a video that will help you learn how to write your own electron configurations.