Protons, neutrons and electrons

• Atom


  The smallest particle of an element that can exist on its own in a stable environment
• Subatomic particles


  • Protons
  • Neutrons
  • Electrons
• Subatomic particles


  • Relative mass
  • Relative charge
  • Position in the atom
• The mass is given relative to the mass of a proton
• The nucleus contains protons and neutrons
• Atomic number


  The number of protons in an atom
• Mass number


  The total number of protons and neutrons in an atom
• The atomic number equals the number of electrons in an atom
• Calculating the number of protons, neutrons and electrons in an atom


  1. Number of protons = atomic number

  2. Number of electrons = atomic number

  3. Number of neutrons = mass number - atomic number
• Radioactive decay occurs when unstable nuclei spontaneously change into more stable ones by emitting particles or energy.
• Isotopes are atoms with the same number of protons but different numbers of neutrons.
• Proton number = atomic number
• The mass number of an atom is the sum of the number of protons and neutrons in the nucleus.
• The atomic number of an element is equal to the number of protons in the nucleus of an atom.