Key words

Dobereiners triads

a triad is a group of three elements with similar chemical properties, in which the atomic weight of the middle element is approximately equal to the average of the other two atomic weights

Newlands octaves

groups of 8 elements arranged in order of increasing atomic weight, in which every eight element has similar properties

Mendeleevs Periodic Law

elements are arranged in order of increasing weight and the properties vary periodically

Atomic number

is the number of protons in the nucleus of the atom

Relative Atomic Mass

the average mass of an atom of the element relative to one twelfth of the mass of a carbon-12 atom