# Ground State Electron Configuration: Definition & Example

The atom’s electron structure is very important because it tells us about an atom’s reactivity, and physical properties as well. In this lesson, we will cover the ground state electron configuration, which determines the electron’s structure.
Electron Configuration Defined
Just like we have a place to live, in the world of subatomic particles, electrons also have their own place. Where they go is dictated by the electron configuration, which describes the electron arrangement within an atom.
For electrons, there is a ground state and an excited state. In this lesson, we’ll be discussing the ground state electron configuration. When we talk about the ground state electron configuration, we’re talking about the electron configuration of an atom at the lowest energy level possible.
In the universe, the natural state of a system is to use the lowest energy possible, so for an atom’s electrons at the ground state, the electron arrangement will be at the lowest energy state that is possible for that atom.
SPDF Notation
The periodic table is divided into s, p, d and f blocks. The s, p, d and f subshells have a maximum number of electrons associated to them, as seen in this table:
Table: s, p, d, f subshells
S-P-D-F Block
The numbers in front of the s, p, d, and f blocks on the periodic table signify the energy levels. Let’s look at the elements sodium (Na), aluminum (Al) and potassium (K). Their positions are indicated on the periodic table seen here:
Al, Na, K: SPDF Blocks
If we count all the way from left to right, and down to where the elements are located on the table, we get the configurations:
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Another guideline to determine the electron configuration is the Diagonal Rule, which shows an spdf chart outlining the exact order that the orbitals are supposed to be filled:
Diagonal Rule
This illustration shows the order of the s, p, d and f orbitals for each energy level and the superscripts (the little numbers) show the maximum number of electrons allowed. This method can also be used to determine the electron configuration.
Looking only at the diagonal spdf chart, we can determine the electron configuration for rubidium (Rb), tellurium (Te) and barium (Ba):
Electron Configuration
Occupancy Rules and Principles
There are rules and principles that must be followed so that the electrons can occupy the orbitals around the atom at the lowest energy arrangement possible. Let’s look at those in more detail.
Aufbau principle: When you think about picking a room at a hotel without an elevator, you will naturally choose a room nearest to you on the ground floor if you have a lot of luggage. Electrons in the ground state behave the same way and this is demonstrated by the Aufbau principle. The Aufbau principle states that electrons occupy the lowest energy orbitals first, before occupying the higher energy orbitals.
Aufbau Diagram
As you go higher, the energy level increases, with 1s having the lowest energy, and 4p having the highest energy, as shown in the illustration.
The Aufbau principle has some exceptions. Fully filled or half filled d orbitals are stable, so, some rearranging is necessary if a d orbital has 4 or 9 electrons. An electron from the s orbital will transfer to the d orbital. A good example is chromium (CR):
Aufbau Principle: Exception
Another example is silver, whose symbol on the periodic table is Ag:
Silver Electron Configuration: Aufbau Exception

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