Atomic Orbitals

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A series of free High School Chemistry Video Lessons.

In this lesson, we will learn

  • Atomic Orbitals
  • Orbital Diagrams
  • Electron Configuration
  • Exception to Electron Configuration
  • Valence Electrons

Atomic Orbitals
Atomic orbitals are regions of space in which electrons can be found. Each orbital can fit two electrons and different orbitals have different shapes. The s sub-level has one spherically shaped orbital, while the p sub-level has three dumbbell shaped orbitals. The arrangement of electrons in orbitals can be depicted using either orbitals diagrams or electron configuration notation.

Understanding the electronic structure of an atom

What are atomic orbitals?
How they are defined, shapes, how they are filled, what they represent

Orbital Diagrams
Orbital diagrams are pictorial descriptions of the electrons in an atom. Three rules are useful in forming orbital diagrams. According to the Auf Bau Principle, each electron occupies the lowest energy orbital. The Pauli Exclusion Principle says that only two electrons can fit into an single orbital. Hund’s rule states that electrons go into different orbitals in the same sub-level before doubling up inside orbitals.

How to depict the electronic configuration of atoms using orbital diagrams

Electron orbital diagrams showing energy levels (n), subshells or sublevels(s, p, d, f), and orbitals

Electron Configuration
Electron configuration is shorthand for the arrangement of electrons in atomic orbitals. It is written out, as opposed to orbital diagrams which are depicted pictorially. For elements with many electrons, noble gas configuration is a useful way to abbreviate the electron configuration.

How to express the electronic structure of atoms using electron configuration notation?
Errata: The Electron Configuration for Cl should be [Ne]3s23p5

Orbital-sublevel arrangement and writing electron configurations
Aufbau principle is used to fill orbitals.

Orbital notation and noble gas configurations
Pauli Exclusion Principle and Hund’s Rule are demonstrated through orbital notation.

Exception to Electron Configuration
There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.

Understanding the exceptions to electron configuration.

Anomalies for electron configurations
Cu and Ag (exceptions to the general rules)

Electron Configuration - Exceptions
(Cr & Mo) (exceptions to the general rules)

Valence Electrons
Valence electrons are the outer electrons that are involved in bonding. Only electrons in the s and p orbitals are valance electrons, so a given atom can have between 0 and 7 valance electrons. Atoms with 0 valence electrons are called noble gases and don’t like form bonds. An atom’s valence electrons can be depicted pictorially using Lewis Dot Diagrams.

How an atom’s outermost electrons contribute to bonding?

Looking at valence electrons to figure out reactivity

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