Atomic structure, isotopes & electron shells

• Relative mass of a proton

  1
• Relative mass of a neutron

  1
• Overall charge of an atom

  Neutral (0)

  If it isn’t neutral then it’s an ion not an atom
• Why are atoms neutral

  Same number of protons and electrons so the charges cancel out
• Atomic number

  Number of protons.

  Number of electrons if it has a neutral atom
• Mass number

  Total number of protons + total number of neutrons
• Isotopes

  Different forms of the same element that have the same number of protons but a different number of neutrons
• What happens if electrons gain energy

  They increase their energy level

  If they gain enough energy they could leave the atom turning the atom into a +1 ion
• Ionising radiation

  Radiation that has enough energy to knock electrons off atoms