Structure of the atom
All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. are very small, they have a radius of around 1 Ă— 10-10 metres.
The modern view of the atom is of a The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. containing Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. and Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. with smaller electrons orbiting outside the nucleus.
The nucleus has a diameter of around 1 Ă— 10-15 metres
Each particle has its own charge and its own mass.
| Relative charge | Relative mass | |
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1840 (Close to 0) |
| Proton | |
| Relative charge | +1 |
| Relative mass | 1 |
| Neutron | |
| Relative charge | 0 |
| Relative mass | 1 |
| Electron | |
| Relative charge | -1 |
| Relative mass | 1/1840 (Close to 0) |
Mass number A and atomic number Z
Protons and neutrons are the heaviest particles in an atom and as a result they make up most of its mass.
The mass of electrons is very small and often not considered to be significant.
The number of protons is what defines the element, ie an atom with six protons in its nucleus will always be carbon, and uranium will always have 92 protons.
An atom is neutral and so the number of electrons is always the same as the number of protons.
If the atom becomes To ionise is to convert an uncharged atom or molecule into a charged particle by adding or removing electrons. however, the number of electrons will change.
An ion is an atom that has lost or gained one or more electron.