L1 Atoms

• Elements are made up of atoms.
• Atoms are made up of three sub-atomic particles.
• • protons: positive charge (nucleus)
  • neutrons: no charge (nucleus)
  • electrons: negative charge (orbit around outside of nucleus)
• All atoms are neutral because they contain the same number of protons and electrons; therefore, their charges cancel out.
• Atomic number is the number of protons (and therefore equal to the number of electrons) in an atom of an element.
• The mass number is the sum of the protons (or electrons) and neutrons in an atom.
• Isotopes: atoms of the same element, with the same mass number, with different numbers of neutrons.