# Electric Charge in the Atom

## Atoms contain negatively charged electrons and positively charged protons; the number of each determines the atom's net charge.

#### Key Points

• A proton is a positively charged particle located in the nucleus of an atom. An electron has $\frac{1}{1836}$ times the mass of a proton, but an equal and opposite negative charge.

• An elementary charge -- that of a proton or electron -- is approximately equal to 1.6×10-19 Coulombs.

• Unlike protons, electrons can move from atom to atom. If an atom has an equal number of protons and electrons, its net charge is 0. If it gains an extra electron, it becomes negatively charged and is known as an anion. If it loses an electron, it becomes positively charged and is known as a cation.

#### Terms

• the massive, positively charged central part of an atom, made up of protons and neutrons

#### Figures

1. ##### Planetary Model of an Atom

Small electrons orbit the large and relatively fixed nucleus of protons and neutrons.

2. ##### Electric Charge

A brief overview of atoms, ions, and electrical charge.

## Overview of Atomic Electrical Charges

Atoms, the fundamental building blocks of all molecules, consist of three types of particles: protons, neutrons, and electrons. Of these three subatomic particle types, two (protons and electrons) carry a net electric charge, while neutrons are neutral and have no net charge.

Both protons and electrons have charge that is quantized. That is, the magnitude of their respective charges, which are equal each other, is 1. This standard value is equal to approximately 1.6×10-19 Coulombs.

### Protons

Protons are found in the center of the atom; they, with neutrons, make up the nucleus. Protons have a charge of +1 and a mass of 1 atomic mass unit, which is approximately equal to 1.66×10-24 grams. The number of protons in an atom defines the identity of the element (an atom with 1 proton is hydrogen, for example, and an atom with two protons is helium). As such, protons are relatively stable; their number rarely changes, only in the instance of radioactive decay.

### Electrons

Electrons are found in the periphery of the atom and have a charge of -1. They are much smaller than protons; their mass is $\frac{1}{1836}$ amu. Typically in modeling atoms, protons and neutrons are regarded as stationary, while electrons orbit very rapidly. The patterns in in which electrons orbit is extremely complex and is of no importance to the discussion of electric charge in the atom. More important is the fact that electrons are labile; that is, they can be transferred from one atom to the next. It is through electronic transfer that atoms become charged.

### Ions

In the ground state, an atom will have an equal number of protons and electrons, and thus will have a net charge of 0. However, because electrons can be transferred from one atom to another, it is possible for atoms to become charged. Atoms in such a state are known as ions.

If a neutral atom gains an electron, it becomes negative. This kind of ion is called an anion.

If a neutral atom loses an electron, it becomes positive. This kind of ion is called a cation.

The steady flow of electrons is called current. Current is what flows through electrical wires and powers electronics items, from light bulbs to televisions.

Figure 2

#### Key Term Glossary

atom
The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons.
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coulomb
In the International System of Units, the derived unit of electric charge; the amount of electric charge carried by a current of 1 ampere flowing for 1 second. Symbol: C
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current
The time rate of flow of electric charge.
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decay
to change by undergoing fission, by emitting radiation, or by capturing or losing one or more electrons
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electric charge
A quantum number that determines the electromagnetic interactions of some subatomic particles; by convention, the electron has an electric charge of -1 and the proton +1, and quarks have fractional charge.
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element
Any one of the simplest chemical substances that cannot be decomposed in a chemical reaction or by any chemical means and made up of atoms all having the same number of protons.
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ground state
the stationary state of lowest energy of a particle or system of particles
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light
The natural medium emanating from the sun and other very hot sources (now recognised as electromagnetic radiation with a wavelength of 400-750 nm), within which vision is possible.
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magnitude
A number assigned to a vector indicating its length.
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mass
The quantity of matter which a body contains, irrespective of its bulk or volume. It is one of four fundamental properties of matter. It is measured in kilograms in the SI system of measurement.
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nucleus
the massive, positively charged central part of an atom, made up of protons and neutrons
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particle
A very small piece of matter, a fragment; especially, the smallest possible part of something.
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power
A measure of the rate of doing work or transferring energy.