The development of the Periodic Table (pre-16)

Julius Lothar Meyer – the first identifier of periodicity?

Most people regard Mendeleev as the initial formulator of the Periodic Table with the work of his contemporaries often ignored. One such chemist was the German Julius Lothar Meyer, (1830 - 1895), who was just four years older than the Russian.

In 1864, five years before the first announcement of a Periodic System by Mendeleev, Meyer had produced a table of just 28 elements which he listed by their valence. [The term valence is now called valency and represents ‘combining power’ of an element. For example sodium forms a chloride NaCl and has a valency of one; magnesium forms MgCl2 and has a valency of two and so on.] The 28 elements were almost entirely main group elements. He incorporated transition metals in another table in 1868 which listed the elements in increasing weight order with elements with the same valence in a given column. This was earlier than Mendeleev's table (1869) but unfortunately Meyer's was not published until 1870.

Mendeleev and Meyer were unaware of each other’s work until after this. Later, Meyer admitted that the Russian had first published about the Periodic System by saying that his ideas matched those of Mendeleev.

However Meyer’s main contribution was his recognition of periodic behaviour, ie a repeating pattern of a property shown on a graph. In the case of Meyer, the property he chose was the atomic volume of an element and he plotted against its atomic weight.

The graph below clearly shows a periodic pattern as the atomic volume rises to peaks and then falls again.


Atomic volume is the volume of a mole of atoms (using modern terminology) and is therefore a measure of the size of an atom of a particular element provided that the element is in the solid state where the atoms are packed closely together.

Activity

You can investigate Meyer’s graph using a spreadsheet. The data on the spreadsheet is modern and is therefore more accurate than that which Meyer had. It also includes the elements discovered since Meyer’s time. You could eliminate these by using the interactive Periodic Table to find which elements were known in Meyer’s time (1868). You can use the spreadsheet to calculate the atomic volume of each element and then to plot this quantity against relative atomic mass. You should also omit from your graph elements that are not in the solid state at room temperature. This is because in liquids and especially in gases, the atoms are not packed closely together so the volume of a mole of atoms does not tell us much about the size of the atoms of an element (it actually tells us about the spacing between them).

Questions

Q 1.     What is the valency of the metal in the following compounds: CrCl2, CrCl3, TiCl2, TiCl4?

Q 2      What sorts of elements are at the peaks of Meyer’s graph?

Q 3.     Explain why oxygen, nitrogen and fluorine are missing from Meyer’s graph.

Click here to see the answers