Structure of the atom
Protons, neutrons and electrons
Atoms are very small, they have a radius of around 1 脳 10-10 metres.
The modern view of the The smallest part of an element that can exist. 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 Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. orbiting outside the nucleus.
Each particle has its own charge and its own mass.
| Relative charge | Relative mass | |
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | Close to 0 (1/2,000) |
| Proton | |
|---|---|
| Relative charge | +1 |
| Relative mass | 1 |
| Neutron | |
|---|---|
| Relative charge | 0 |
| Relative mass | 1 |
| Electron | |
|---|---|
| Relative charge | -1 |
| Relative mass | Close to 0 (1/2,000) |
Mass number and atomic number
Protons and neutrons are the heaviest particles in an atom and as a result they make up most of the The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of the atom. The mass of electrons is often not considered to be significant.
The number of protons is what defines the A substance made of one type of atom only., ie an atom with six protons in its nucleus will always be carbon, and uranium will always have 92 protons.
In a neutral atom, 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.
Using atomic symbols
Mass number and atomic number are two important pieces of information about an atom.
An atom can be represented using the symbol notation:
\(_{Z}^{A}\textrm{X}\)
Where:
- A is the mass number
- Z is the atomic number
- X is the symbol
For example, chlorine (Cl) can be shown as:
This symbol shows that chlorine has 35 particles in the nucleus (protons and neutrons), 17 of which are protons. It also tells us that chlorine has 18 neutrons (35 - 17) and, as the number of electrons and protons are equal in a neutral atom, chlorine also has 17 electrons.