Electron Configuration Worksheet
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Study Guides
Big Picture
Electrons are tiny, negatively charged particles found in regions called orbitals around the nucleus of an atom. Each
element has a different number of electrons, and each electron in the atom has its own unique set of quantum
numbers. The electrons and the neutron interact and form the most stable arrangement possible. An atom’s electron
configuration is the arrangement of the electrons.
Key Terms
Ground State: Lowest energy state. All electrons are in the lowest energy orbitals.
Electron Configuration: Notation used to describe the way an atom’s electrons are arranged into orbitals. Electrons
are listed in order from lowest energy to highest.
Aufbau Principle: Electrons will fill the lowest energy state available within an atom and only occupy a higher energy
state if all lower states are full.
Pauli Exclusion Principle: Electrons cannot have the same four quantum numbers within the same atom.
Hund’s Rule: Each orbital in a set must have one electron before it gets a second.
Three Rules
There are three rules for determining the ground state electron configuration of an atom: the Aufbau principle, the
Pauli exclusion principle, and Hund’s rule.
1. When placing an electron into an orbital, follow the Aufbau principle (also called the building-up principle): an
electron occupies orbitals in order from lowest to highest energy.
2. According to the Pauli exclusion principle, no more than two electrons can be placed in any orbital.
3. Before a second electron can be placed in any orbital, follow Hund’s rule: all the orbitals of that sub-level must
contain at least one electron before a second electron can be added.
Atoms are not really built by adding protons and electrons one at a time! The Aufbau principle is just a way
to determine the electron configuration.
Orbital Filling Diagram
A convenient visual way to represent the arrangement of electrons in an atom is the orbital filling diagram. In an orbital
filling diagram:
•
Each orbital is represented as a square (or a circle).
•
Electrons are represented as arrows drawn inside the square (or circle).
•
The arrow can point either up or down.
•
Each sublevel is labeled by the principal energy level and sublevel.
•
l
Example: 1s has principal energy level (n) = 1 and sublevel (
) = 0
The Aufbau principle, Pauli exclusion principle, and Hund’s rule can be used to complete an orbital filling diagram.
Aufbau Principle
The diagram to the right shows the energy levels of
various atomic orbitals. The diagram shows that:
Image credit
•
Orbitals of greater energy are higher up on the
diagram.
•
Orbitals in the same sublevel of a principal energy
level are drawn next to each other horizontally and
are of equal energy.
•
The s sublevel within a principal energy level is always
the lowest in energy.
•
The energy levels of one principal energy level can
overlap with the energy levels of another principal
energy level.
•
Example: the 4s sublevel is lower in energy than
the 3d sublevel
Image Credit: CK-12 Foundation, CC-BY-NC-SA 3.0
This guide was created by Steven Lai, Rory Runser, and Jin Yu. To learn more
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about the student authors, visit
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