Partial charge

A partial charge is an electric charge on an atom which is smaller in magnitude than the charge of a single electron or proton. Because electrons have the smallest charge of any free particle, partial charges can't exist on large objects, and are only found inside molecules. Partial charges are used to indicate whether a covalent bond between atoms is polar.

Partial charges are usually written using the Greek letter delta, and a symbol to indicate their sign: δ+ for a positive partial charge, and δ- for a negative one. The numeric value of a partial charge is usually less important than its sign, and can be measured in a few different ways, so it's rare that exact numbers are given for partial charges.

Partial charges are formed when two different chemical elements have different electronegativity, a number that measures how much each element wants to gain electrons. Atoms which pull harder on electrons will attract negative charge, and those which have a weaker pull have a positive charge.

In water, H
2O, oxygen wants electrons more than hydrogen does. Hydrogen then has a positive partial charge δ+ and oxygen has a negative partial charge δ-.