The electric charge is a physical quantity that determines the intensity of electrostatic interactions.

Simplified scheme of a Helium atom. The electrons are represented by the red spheres that orbit the kernel, constituted of protons and neutrons (blue and green spheres). Electrons, because they are on the periphery, are "easier" to be "ripped out". While the kernel is more strongly connected and is difficult to be dismembered. There are more modern models of atoms developed in the theory known as quantum mechanics, but for many applications, this simpler model is enough to describe well several physical phenomena.

Electrical charge

Types of electric charges
There are only two types, positive and negative.
Du Fay's Principle
Two bodies electrified with different charges (one positive and one negative) attracts each other. Bodies with the same type of charges (both positive or both negative) repel each other.
Illustration of forces between electrified bodies. a) oppositely charged bodies attract each other and b) bodies with the same charges repel each other.
Conservation of Electric Charges
The total amount of electrical charges does not change in any process performed within an isolated system.
Quantization of Electric Charge
All charges that are observed in nature are equal or multiple of the elementary charge \(e\).
Elementary Electric Charge
Electron: \(-e\) (negative elementary charge)
Proton: \(+e\) (positive elementary charge)
where \(e = 1,6 \times 10^{-19} C\) .
The electric charge unit in \(IS\) is the Coulomb (\(C\)).

The net amount of charge\((Q)\)

The net charge a body possesses is equal to the number of excess of elementary charges (positive or negative) times the elementary charge, i.e., \begin{equation} Q = ne, \end{equation} where \(n\) is the number of electrons transferred or received, and \(e\) is the value of the elementary charge.

Every atom is electrically neutral if its number of protons is equal to the number of electrons.