Properties of Atoms
Particles
Proton, relative charge = +1, relative mass = 1
Neutron, relative charge = 0, relative mass = 1
Electron, relative charge = -1, relative mass = negligible
Atoms are neutral, because the number of protons is equal to the number of electrons.
The atomic number of an element is determined by the number of protons in an atom.
An atom is very small, having a radius of approximately 0.1 nm.
The radius of the nucleus is approximately 1/10,000th of the atom.
The mass number tells you the total number of protons and neutrons in an atom.
Mass number – atomic number = number of neutrons
The video below explains the properties of atoms.
Isotopes
Some atoms can have different numbers of neutrons. These atoms are called isotopes. The existence of isotopes results in the relative atomic mass of some of the elements, e.g. chlorine, not being whole numbers.
Chlorine exists as two isotopes. Chlorine-35 makes up 75% of all chlorine atoms. Chlorine-37 makes up the other 25%. The abundance of chlorine-35 is 75%.
(mass of isotope 1 x abundance) + (mass of isotope 2 x abundance) / 100
(35 x 75) + (37x25) / 100 = 35.5
Glossary of terms
Mass number: The total number of protons and neutrons in an atom.
Atomic number: The number of protons in the nucleus of the atom.
Isotopes: Atoms of the same element that have the same number of protons but different numbers of neutrons.
