Henry Moseley

Problems with Bohr’s Model Only valid for Hydrogen Bohr’s Model was the first to connect energy to the Atomic Model, but it fails to explain the spectra of larger atoms. In particular, it falls apart when the atom has more than one electron in its outermost orbit.

Moseley’s Experimental Design X-ray Diffraction Nearly every element from Al to Au I used x-ray diffraction to study the relationship between the atomic number of an element and its x-ray spectroscopy. I focused specifically on the shortest wavelength line found in the spectrum. I used other scientists’ techniques and designs, as well as some of my own, to develop x-ray spectrometry equipment that can be used to study the elements. I studied the data for nearly every element from aluminum to gold.

Supporting Evidence K alpha lines In particular Cobalt and Nickel The shortest wavelength line in the x-ray spectra is called the K alpha line. I discovered a correlation between this line and the atomic number of an element. The energy associated with this line corresponds to a value of Z-1, or the atomic number of the element minus one. At first, I couldn’t explain why this happened. Other scientists determined that this occurred when one electron was knocked out of the lowest orbital, leaving only one electron left in that orbital. Electrons in the second orbital, or n=2, have an effective charge of Z-1 due to the one electron left in the first orbital. When the n=2 electron drops to the first orbital, the energy emitted corresponds to the K alpha line.

Modifications to Atomic Model Defined the nuclear charge of an element as equal to its atomic number. My work led to evidence supporting the idea that an element’s nuclear charge equals its atomic number. Prior to this, atomic number had been an arbitrary number linked to its location on the Periodic Table.

Supporting Mendeleev The atomic number now had meaning, rather than being arbitrarily assigned. Mendeleev initially organized the Periodic Table by putting elements in order based on their atomic weights. However, when doing this, he switched Iodine and Tellurium because he felt they belonged in different locations based on their properties. My work supports Mendeleev’s switch because Iodine’s atomic number is larger than Tellurium’s. In addition, after my work, the locations of Cobalt and Nickel were switched on the Periodic Table. My discoveries directly led to the development of the Periodic Law.

Fun Facts I was a well respected scientist that many expected great things from. However, when WWI broke out in 1914, I enlisted in the Royal Engineers. In 1915, I was shot by a sniper and killed. Some said my death was the single most costly death of the war to mankind. It was due to my death that the British and other world governments no longer allowed their scientists to go to war. And, I should have won the Nobel Prize!

Resources Wikipedia – Henry Moseley Blabberize.com Chemistry Encyclopedia – Henry Moseley www.chemistryexplained.com