|
|
|
|
Lothar MeyerIn 1870, Lothar Meyer, a German chemist, made a chart that plotted atomic volumes
against atomic weight. That plot is shown here using data from the "Periodic Chart of
the Atoms" (1979 Edition, Sargent-Welch Scientific Company). |
|
Distance Learning questions Clackamas Community College |
He
measured the volume of one atomic weight's worth of each element--that is, one mole--and
figured that since the number of atoms in each amount was the same, the volumes measured
must represent the relative volumes of the individual atoms. By plotting those volumes
against the atomic weights you can see that there is a recurring pattern--sort of like
waves with the crests and the troughs, or hills and valleys. We can start with the element
at the top of each one of those peaks. They are lithium, sodium, potassium, rubidium, and
cesium. Following each of those there is a repeating pattern. An important observation
that Meyer made was the change in length of that repeating pattern. Unlike Newslands’
octaves, these groups were not all the same length. Hydrogen was sort of a group all by
itself, lithium through fluorine was another group, sodium through chlorine was another,
potassium through bromine, and so on. Notice that there are small groups at the beginning
and then larger groups afterwards. In summary, there is repeating periodicity of the
atomic volume, but the periods changed in size. The first period is one element in
length--hydrogen. The second and third periods are seven in length. The fourth and fifth
periods are seventeen elements in length. Subsequent to Meyer's work we discovered all of
the inert gases, so we now have one more element in each period--making 2, 8, 8, 18, 18.
