Henry Moseley (1887 - 1915)

Studied Rutherford's discoveries that an atom has positive particles and empty space.

Arranged the periodic table in orber based on the atomic number of the elements and discovered isotopes of elements. He discovered the relationship between atomic number and x-ray frequencies.  He then developed the use of X-ray specra to study atomic structure. 

Discovered the mass of a proton which was 1 amu by analyzing the results of his x-ray experiment.

Moseley discovered the wavelengths of the X-ray spectral lines. He published his measurements of wavelengths of the X-ray, which he then used to order the elements in order by atomic number.