IB Chemistry home > Syllabus 2016 > Fundamental concepts > The forces of nature

There are four fundamental forces in nature that can act over a distance. We are very familiar with gravity, for example, and accept that it acts on any object in a gravitational field.

Two of the other forces are applicable only to the nuclei of atoms and, as such, do not concern us here. The fourth force is the electromagnetic force.

This has various manifestations, such as a magnetic field acting on magnetic materials. One other manifestation of this force is the electrostatic field that is associated with charged particles. This is the force responsible for the structure of all matter.

Electrical charge

Some of the fundamental sub-atomic particles carry electrical charges. These are static electrical charges; they are a characteristic of the particle itself and cannot be lost.

The words 'positive' and 'negative' are just conventions to describe the opposite nature of the two types of charge.


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Electrostatic field

An electrically charged particle has an associated electrostatic 'field'. This means that any other charged particle entering that region of space experiences a force. If the approaching particle has the same electrical charge, then it feels a repulsive force. If it has an opposite electrical charge it feels an attraction.

An electrostatic field cannot be seen (unlike the demo), but it is there nevertheless and any other charged particle entering this region of space feels a corresponding force due to this field.


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Electrostatic force

The forces created by electrostatic fields interacting are very straightforward. Positively charged particles attract negatively charged particles, and vice versa. This force of attraction acts along an imaginary line joining the centres of the two charges.

Particles with like charges, i.e. both negative, or both positive, repel one another.

This effect is the fundamental force behind the formation of all matter. Atoms are held together by electrostatic forces, atoms are bonded to one another by electrostatic forces, molecules are attracted to one another by electrostatic forces, metals are held together by electrostatic forces and finally ionic compounds are held together by electrostatic forces.

You could say that without this force there would be no universe.


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Forces in atoms

Atoms have protons in the nucleus and electrons in regions of space around the outside of the atom. The nucleus of atoms is positively charged and the individual electrons each have a single negative charge. Atoms are always neutral, meaning that the number of protons, and the magnitude of the positive charge, is always balanced by the same number of electrons and negative charge.

Example: The hydrogen atom.

1 proton, 1 electron= 1 positive charge and 1 negative charge

Overall charge  1 + 1- = 0


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Forces between atoms

When there is a force of attraction between positive and negative charges from different atoms, it draws the atoms together and holds them in position. This is called a chemical bond. The bonded atoms have lower overall energy than the individual component atoms, so the bonded situation is more stable and preferred.

Even though the positive nucleus has its charge balanced by the electron cloud, a single electron approaching from one side will experience the repulsion from the electrons that are nearest, but will be more powerfully attracted by the nucleus. This also applies to electrons in different atoms; they are attracted to neighbouring atoms.

It is this force of attraction between the nucleus of one atom and the the electrons of another that is the basis of chemical bonding. These forces have the effect of holding the nucleus of one atom to the nucleus of another atom, i.e. bonding the two atoms together.

In reality, these bonding forces take slightly different forms in different situation, but it is true that we are always dealing with some kind of electrostatic force between atoms.


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