Chemistry Definitions: What are Electrostatic Forces?

There are several types of forces that relate to science. Physicists deal with the four fundamental forces: gravitational force, weak nuclear force, strong nuclear force, and electromagnetic force. The electrostatic force is associated with the electromagnetic force.

Electrostatic Forces Definition 

Electrostatic forces are attractive or repulsive forces between particles that are caused by their electric charges. This force is also called the Coulomb force or Coulomb interaction and is so named for French physicist Charles-Augustin de Coulomb, who described the force in 1785.

How the Electrostatic Force Works

The electrostatic force acts over a distance of about one-tenth the diameter of an atomic nucleus or 10^-16 m. Like charges repel one another, while unlike charges attract one another. For example, two positively charged protons repel each other as do two cations, two negatively charged electrons, or two anions. Protons and electrons are attracted to each other and so are cation and anions.

Why Protons Don't Stick to Electrons

While protons and electrons are attracted by electrostatic forces, protons don't leave the nucleus to get together with electrons because they are bound to each other and to neutrons by the strong nuclear force. The strong nuclear force is much more powerful than the electromagnetic force, but it acts over a much shorter distance.

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Coulomb's Law Definition in Science

By Anne Marie Helmenstine, Ph.D.

In a sense, protons and electrons are touching in an atom because electrons have properties of both particles and waves. The wavelength of an electron is comparable in size to an atom, so electrons can't get closer than they already are.

Calculating the Electrostatic Force Using Coulomb's Law

The strength or force of the attraction or repulsion between two charged bodies can be calculated using Coulomb's law:

F = kq₁q₂/r²

Here, F is the force, k is proportionality factor, q₁ and q₂ are the two electric charges, and r is the distance between the centers of the two charges. In the centimeter-gram-second system of units, k is set to equal 1 in a vacuum. In the meter-kilogram-second (SI) system of units, k in a vacuum is 8.98 × 109 newton square meter per square coulomb. While protons and ions have measurable sizes, Coulomb's law treats them as point charges.

It's important to note the force between two charges is directly proportional to the magnitude of each charge and inversely proportional to the square of the distance between them.

Verifying Coulomb's Law

You can set up a very simple experiment to verify Coulomb's law. Suspend two small balls with the same mass and charge from a string of negligible mass. Three forces will act upon the balls: the weight (mg), the tension on the string (T), and the electric force (F). Because the balls carry the same charge, they will repel each other. At equilibrium:

T sin θ = F and T cos θ = mg

If Coulomb's law is correct:

F = mg tan θ

The Importance of Coulomb's Law

Coulomb's law is extremely important in chemistry and physics because it describes the force between parts of an atom and between atoms, ions, molecules, and parts of molecules. As the distance between charged particles or ions increases, the force of attraction or repulsion between them decreases and the formation of an ionic bond becomes less favorable. When charged particles move closer to each other, energy increases and ionic bonding is more favorable.

Additional References

• Coulomb, Charles Augustin (1788) [1785]. "Premier mémoire sur l'électricité et le magnétisme." Histoire de l’Académie Royale des Sciences. Imprimerie Royale. pp. 569–577.
• Stewart, Joseph (2001). "Intermediate Electromagnetic Theory." World Scientific. p. 50. ISBN 978-981-02-4471-2
• Tipler, Paul A.; Mosca, Gene (2008). "Physics for Scientists and Engineers." (6th ed.) New York: W. H. Freeman and Company. ISBN 978-0-7167-8964-2.
• Young, Hugh D.; Freedman, Roger A. (2010). "Sears and Zemansky's University Physics: With Modern Physics." (13th ed.) Addison-Wesley (Pearson). ISBN 978-0-321-69686-1.