Difference Between Atom and Ion

The key difference between atom and ion is their charge; atoms are neutral while ions are charged positively or negatively.

Atom is the smallest neutral unit which can form bonds while ion is any charged molecule. Ion may be composed of several atoms or a single atom. Atoms are unique and do not differentiate into various types while ions have two types as positive ions (cations) and negative ions (anions).

CONTENTS

1. Overview and Key Difference
2. What is an Atom 
3. What is an Ion
4. Side by Side Comparison – Atom vs Ion in Tabular Form
5. Summary

What is an Atom?

Atom is the smallest unit of matter, and a certain atom represents the properties of the chemical element to which it belongs. All gases, solid matter, liquids and plasma consist of atoms, which are very small units whose size is around 100 picometers.

When considering the structure of an atom, it contains a nucleus and electrons moving around the nucleus. Furthermore, protons and neutrons (and there are some other subatomic particles as well) make up the atomic nucleus. Typically, the number of neutrons, protons and electrons are equal to each other, but in the case of isotopes, the number of neutrons is different from that of protons. We call both protons and neutrons “nucleons”.

Around 99% of the atom’s mass is centred in the nucleus because the mass of an electron is almost negligible. Among these subatomic particles, a proton has +1 charge; an electron has -1 charge and a neutron has no charge. If the atom has equal numbers of protons and electrons, then the overall charge of the atom is zero; lack of one electron results in a +1 charge and a gain of one electron gives -1 charge to the atom.

What is an Ion?

Ion is a charged chemical species. They always have unequal numbers of electrons and protons. There are two types of ions as cations and anions. Cations have a positive charge due to lack of electrons to balance the charge of protons. Anions, on the other hand, have an excess number of electrons and consist of a negative charge.

Ions are available in all three phases of matter; solid, liquid and gas phases. Some ions are single atoms with a charge, but most of the times, ions are polyatomic.

What is the Difference Between Atom and Ion?

The key difference between atom and ion is the charge. Atom is electrically neutral while ion is electrically charged. Atom always contains an equal number of electrons and protons, but in an ion, the number of electrons and protons are always different. The maximum number of positive charges an ion can have is 6; the maximum number of negative charges is 3. This happens due to two reasons. The first reason is the loss of electrons, which results in positive ions. The other reason is the gain of electrons, resulting in negative ions. Atoms always have atomic orbitals while ions have either atomic orbitals or molecular orbitals or both atomic and molecular orbitals. This is another difference between atom and ion. Furthermore, atoms can be found only in the gaseous phase, but ions can be found in the gaseous phase, liquid phase and as well as in solid phase.

Summary – Atom vs Ion

The key difference between atom and ion is the charge. Atom is electrically neutral while ion is electrically charged. An atom always contains an equal number of electrons and protons, but in an ion, the number of electrons and protons are always different.

Image Courtesy:

1. “Atom” By Svdmolen/Jeanot (converted by King of Hearts) – Image:Atom.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Carbonat-Ion” By NEUROtiker ⇌ – Own work, Public Domain) via Commons Wikimedia