atoms and isotopes

• an atom has no overall charge, because the total positive charge equals the total negative charge, because the number of protons equals the number of electrons
• an atom that loses an electron is called an ion and has an overall positive charge
• alpha particles consist of two protons and two neutrons, they consist of a helium nucleus, they are poorly penetrating and can only travel a few cm in the air. Alpha particles can be absorbed by skin and paper
• beta particles are electrons, they can travel several metres in the air and can pass through aluminium and are medium penetrating
• alpha particles and beta particles are deflected in opposite directions in an electric field
• mass is both protons and neutrons added together
• alpha particles can be used to detect smoke for smoke alarms
• fusion happens in a star, chain reactions happen in a nuclear reactor, alpha decay happens in the nucleus of an atom