The lowest energy shell is filled up with two electrons. This explains the chemical inertness of the helium atom. Hydrogen Lightest of the chemical elements, consisting of one proton and one electron besteht. The isotopes deuterium . Ion Electrically charged atom , that lacks one or more electrons .
Ionisation can occur by impact of an energetic electron or photon .
An atom can also be ionised by contact with excited atoms or with a hot surface. Ionosphere Most upper layer of the atmosphere between 60km and 500km altitude, which is ionised by ultraviolet radiation from the Sun. Since the ionosphere represents an electrically conducting plasma . The existence of the ionosphere was deduced from the reflection of radio waves, which allows transatlantic short-wave communication. Isotope Atomic nuclei with same number of protons but different number of neutrons are called isotopes.