Moseley investigated systematically, the characteristic radiations emitted by different targets. Based on his experiments, he has concluded that the frequency of the spectral line in the characteristic X-ray spectrum is directly proportional to the square of the atomic number (Z) of the element considered. This is known as Moseley's law. i.e ν α Z2 or rt(ν) = a ( Z − b)
where a and b are constants depending upon the particular spectral line.
Applications of Moseley's law
(i) Any discrepancy in the order of the elements in the periodic table can be removed by Moseley's law by arranging the elements according to the atomic numbers and not according to the atomic weights.
(ii) Moseley's law has led to the discovery of new elements like hafnium (72), technetium (43), rhenium (75) etc.
(iii) This law has been helpful in determining the atomic number of rare earths, thereby fixing their position in the periodic table.
A German scientist, Wilhelm Roentgen, in 1895, discovered X-rays when he was studying the phenomenon of discharge of electricity through gases.
After performing a series of experiments, Roentgen concluded that when a beam of fast moving electrons strike a solid target, an invisible penetrating radiation is produced. Due to the unknown nature of the radiation, Roentgen called these radiations as X - rays.
X-rays are electromagnetic waves of short wavelength in the range of 0.5 Å to 10 Å. Roentgen was awarded Nobel prize in 1901 for the discovery of X-rays.