| particle | mass | charge | ||
| kg | amu | coulomb | e | |
| electron | 9.109 x 10-31 | 0 | -1.602 x 10-19 | -1 |
| proton | 1.673 x 10-27 | 1 | +1.602 x 10-19 | +1 |
| neutron | 1.675 x 10-27 | 1 | 0 | 0 |
The number of each type of particle in a given atom can be found from the atomic symbol. To accomplish this, there is a standard notation to indicate the atomic number, the mass number and the charge of the atom. These numbers are indicated by the location of the number in the atomic symbol.
The atomic number is indicated in the lower left-hand corner:
This indicates carbon which has an atomic number of 6. The atomic number indicates the number of protons in the atom.
The mass number is given in the upper left-hand corner:
This indictates a fluorine atom which weighs 19 atomic mass units (amu). The mass number indicates the total number of protons plus neutrons. (Since both protons and nuetrons weigh 1 amu each, it should be clear why the mass number gives the mass in atomic mass units!)
The charge is indicated in the upper right-hand corner:
This indicates an oxygen atom which has an electrical charge of twice that of an electron. Recall that electrons have a negative charge. This is why a charge of twice that of an electron is conveniently indicated as "-2". The charge number is simply the number of protons minus the number of electrons.
Here are some samples:
Patrick E. Fleming
Department of Chemistry and Biochemistry
California State University, East Bay
patrick.fleming@csueastbay.edu