The frequency of X-rays is typically 3 x 1017s-1. This corresponds to a wavelength of approximately 0.01 to 10 nanometers. X-rays have a typical energy of 1.2x105 kJ/mol.
X-rays were discovered on November 8, 1895, by the German physicist Wilhelm Conrad Rontgen. He named his discovery "X-radiation" to show that the radiation type was unknown. X-rays produce electromagnetic energy at wavelengths that are about 1,000 shorter than the ultraviolet rays from light. They are a form of ionizing radiation because they cause an atom or molecule to lose an electron. X-rays allow physicians to see inside the human body without the need for surgery, but carry a risk of radiation exposure, which can lead to cancer.