|  | 4.1 | Basics of Electricity
| 4.1.1 | A helium atom

All matter is composed of atoms. "The Periodic Table of Elements" , lists all known types of atoms and their properties. The names of the parts of the atom are:

- nucleus - the center part of the atom, formed by protons and neutrons
- protons - particles have a positive charge , and along with neutrons, form the nucleus
- neutrons - particles have no charge (neutral), and along with protons, form the nucleus
- electrons - particles have a negative charge, and orbit the nucleus

To help you understand the electrical properties of elements/materials, locate "helium" on the periodic chart. It has an atomic number of 2, which means that it has 2 protons and 2 electrons. It has an atomic weight of 4. By subtracting the atomic number (2) from the atomic weight (4) you learn that helium also has 2 neutrons .

The Danish physicist, Niels Bohr, developed a simplified model to illustrate atoms. This illustration shows the model for a helium atom. Notice the scale of the parts. If the protons and neutrons of this atom were the size of a soccer ball, in the middle of a soccer field, the only thing smaller than the ball would be the electrons. They would be the size of cherries, and would be orbiting near the outer-most seats of the stadium. The only thing larger would be the space inside the atom, which would be the size of the soccer field.

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