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Electromagnetic radiation is absorbed or emitted as electrons move out or in among the shells respectively. Electrons in the higher shells have a higher energy level than those in the inner shells.

A radioactive element has an unstable nucleus. the unstable nucleus will Decay by emitting particles until it becomes stable.

Four types of nuclear radiation, defined by the type of particle emitted from the nucleus.

• Alpha particle, same structure as a helium nucleus.
• Beta particle, Electron, formed when a neutron splits into a proton and an electron
• Gamma rays, a type of electromagnetic radiation
• Neutron

Naming systems

Why the word hydrogen?