The atom is the basic unit of matter, which consists in a dense central nucleus, surrounded by electrons negatively charged. The central nucleus contains a mix of protons positively charged and neutral neutrons.
An atom can be:
- Electrically neutral – has an equal number of protons and electrons;
- Positive electrical charge – has less electrons than protons (it is also known as “electron deficiency”)
- Negative electrical charge – has less protons than electrons (it is also known as “electron excess”).
The atom which is positively or negatively charged is known as ion.
A group of atoms, which are bound together, form a molecule.
An atom is classified according to the number of protons and neutrons in its nucleus:
- The number of protons determines the chemical element;
- The number of neutrons determines the isotope of the element.
Atoms are minuscule objects with proportionately tiny masses and can be observed just with special instruments. Most of the mass of an atom is concentrate in the nucleus.
Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element.
The number of protons and neutrons in the atomic nucleus can be modified by nuclear fission, causing a nucleus to split into two smaller nuclei.
The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force.