Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
Organic Chemistry

1.3 Atomic Structure: Electron Configurations

Organic Chemistry1.3 Atomic Structure: Electron Configurations

1.3 • Atomic Structure: Electron Configurations

The lowest-energy arrangement, or ground-state electron configuration, of an atom is a list of the orbitals occupied by its electrons. We can predict this arrangement by following three rules.

The lowest-energy orbitals fill up first, 1s2s2p3s3p4s3d1s2s2p3s3p4s3d, according to the following graphic, a statement called the Aufbau principle. Note that the 4s orbital lies between the 3p and 3d orbitals in energy.

The orbital arrangement featuring orbitals in order 1s; 2s; 2p-3s; 3p-4s; 3d-4p-5s; 4d-5p-6s; 4f-5d-6p; 5f-6d; and 6f. Arrows denote the order in which orbitals are filled with electrons.

Electrons act in some ways as if they were spinning around an axis, somewhat as the earth spins. This spin can have two orientations, denoted as up () and down (). Only two electrons can occupy an orbital, and they must have opposite spins, a statement called the Pauli exclusion principle.

If two or more empty orbitals of equal energy are available, one electron occupies each with spins parallel until all orbitals are half-full, a statement called Hund’s rule.

Some examples of how these rules apply are shown in Table 1.1. Hydrogen, for instance, has only one electron, which must occupy the lowest-energy orbital. Thus, hydrogen has a 1s ground-state configuration. Carbon has six electrons and the ground-state configuration 1s22s22px12py1, and so forth. Note that a superscript is used to represent the number of electrons in a particular orbital.

Table 1.1 Ground-State Electron Configurations of Some Elements
Element Atomic number Configuration
Hydrogen 1 The electron configuration of hydrogen. A 1s orbital contains one electron.
Carbon 6 The electron configuration of carbon. 1s and 2p orbitals contain a pair of electrons. 2p contains two unpaired electrons and a vacant subshell.
Phosphorus 15 The electron configuration of phosphorus. 1s, 2s, 2p, and 3s have paired electrons in their subshells. 3p has three unpaired electrons.
Problem 1-1
What is the ground-state electron configuration of each of the following elements:
Problem 1-2
How many electrons does each of the following biological trace elements have in its outermost electron shell?
Order a print copy

As an Amazon Associate we earn from qualifying purchases.


This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution-NonCommercial-ShareAlike License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at
Citation information

© Jan 9, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.