KEY POINTS
- For the first time the idea of an atom was given by a Greek philosopher “Democritus”.
- In 19th century, John Dalton from England presented the first atomic model.
- According to John Dalton atom neither be created nor destroyed.
- There are three sub-particles of atoms i.e. proton, electron and neutron, these are called fundamental particles.
- The center of the atom is known as “Nucleus”.
- Electron has negative charge, proton has positive charge and neutron has no charge.
- Electron always in constant motion around the nucleus.
- Electrons revolve around the nucleus in particular paths called orbits or shells.
- Atom is a neutral particle i.e. the number of proton just equal to the number of electron.
- The number of protons in the nucleus or the number of electron of an atom is called Atomic number, represented by “Z”.