A chemical element is a species of atoms with a defined amount of protons in its nuclei.
There are currently (as of early 2017) 118 discovered chemical elements (with 1-118 protons in their nuclei).
To describe a chemical element, each have a number, a name, and a chemical symbol. Below, you can see some examples of this:
|Number of protons||Name||Chemical symbol|
The full list of chemical symbols can be found in the periodic system.
When writing a chemical symbol, it's possible to attach different kind of information to it.
- In the bottom left corner, the atomic number is entered. The atomic number is equal to the number of protons. This is often excluded since the chemical symbol is connected to a specific atomic number.
- In the top left corner, the atomic mass is entered (the sum of protons and neutrons).
- In the top right corner, the electrical charge is entered if it's an ion. The charge entered is a net charge in case there are several charged atoms with the same chemical symbol.
- In the bottom right, the number of atoms is entered (if there are several atoms with the same chemical symbol). If the number is equal to 1, it is omitted.
Note that all of this information is not entered at the same time. If you look at individual atoms or ions, the information to the left about atomic mass and atomic number may be included. If we instead look at chemical compounds (which contain two or more different atoms), only the information to the right is relevant (charge and number of atoms).