Atomic structure

• Atoms are neutral because they have equal numbers of positive and negative charges.
• The atomic number is the number of protons in an atom
• The number of protons is the atomic number (Z).
• The mass number (A) is the sum of the proton and neutron masses.
• Isotopes are atoms with different masses but the same number of protons
• Ions are charged particles formed when electrons are lost or gained by an atom, resulting in either a positive charge (cation) or a negative charge (anion)
• In one shell there can only have 2 electrons and the others can only have 8
• Electrons move around the nucleus in energy levels called electron shells
• Atoms that lose electrons become positively charged cations