Before showing you what electric charge is , a discussion of what electrical forces are is important. Keep reading carefully. In the end, you will under why your finger received an electric shock.
Beside the force of gravity acting on you, imagine also another pair of forces that are very powerful acting on you called electrical attracting force and electrical repelling force.
See the electrical attracting force as coming from the earth and the electrical repelling force as coming from your body.
Why don't you feel the effect of this pair of forces?
You don't feel anything because the two forces balance each other.
In the end, you only feel the force of gravity.
Now that you are aware of the presence of electrical forces, where does these force come from?
Electrical forces come from particles in atoms.
Particles in atoms are called electrons, protons, and neutrons.
The model of an oxygen atom is shown below.
In an oxygen atom, there are 8 protons, 8 neutrons, and 8 electrons.
The 8 protons and 8 neutrons form what we call the nucleus.
The nucleus is surrounded by electrons and the electrons are shown in red.
Although it is not clearly shown on the picture above, the mass of a proton is far greater than that of an electron. the mass of a proton is almost 2000 times the mass of an electrons.
It is commonly accepted that an electron carries a negative charge and a proton carries a positive charge. The charge of an electron is equal in magnitude to the charge of an electron.
The protons attract the electrons and hold them in orbit. However, electrons repel other electrons.
Basically, opposite charges attract, but like charges repel.
Under normal condition, there are as many electrons as protons in an atom. we say that the atom has a zero net charge.
If an atom happens to have more electrons or more protons, we call this phenomenon charge or electric charge.
If the number of electrons exceeds the number of protons, the atom is negatively charged.
On the other hand, If the number of protons exceeds the number of electrons, the atom is positively charged.
A neutral atom is an atom that has the same number of electrons as protons.
In the atom shown above, the 2 innermost negatively electrons are attracted a lot to the positively charged nucleus. However, it is not the same of the other 6 outermost electrons. They can easily be cut loose by outside forces.
If an electron is removed or lost, the atom is no longer neutral, it is electrically charged.
Rubber does not easily lose its electrons while this happen a lot easier with silk or human skin. We say that rubber has more electron affinity.
So if you rub silk against rubber, the rubber will gain the electrons lost by the silk.
If you brush electrons onto your feet while walking across a rug, you will be become negatively charged. If you touch a door handle with your finger, you may sometimes experience a small electric shock.
This happened because your body was not neutral, but negatively charged and the door handle was positively charged with less electrons.
The door handle wanted the extra electron(s) from your body.
As the extra electrons transferred from your body to the door handle, you experienced a tiny shock. This is an example of static electricity or electricity at rest since no wires are involved here.
When an atom is electrically charged, the atom has a net charge. An atom that is electrically charged is called an ion. A positive ion has a net positive charge while a negative ion has a net negative charge.
Whenever objects carry a net positive or negative charge, there is an imbalance in electrical charge. As a result, electrical forces will arise that will either cause objects with this imbalance to either attract or repulse each other.