Atomic Structure

• Atoms

  Tiny particles that make up all matter
• Dalton's atomic theory: all matter is made up of tiny particles called atoms, atoms are tiny hard spheres that cannot be broken down, atoms cannot be created or destroyed, atoms of the same element are identical
• Experiments in the late 19th century suggested atoms contain even smaller particles
• Structure of atoms

  • Made up of electrons, protons and neutrons
  • Protons and neutrons in the nucleus, electrons in shells around the nucleus
• Atoms have equal numbers of protons and electrons, so have no overall charge
• Relative mass and charge of subatomic particles

  • Proton mass = 1, charge = +1
  • Electron mass = 1/1835, charge = -1
  • Neutron mass = 1, charge = 0
• Most of the mass of an atom is in its nucleus
• Atomic number


  The number of protons in the nucleus of an atom, defines the element
• Moseley's experiments confirmed the periodic table should be ordered by atomic number, not atomic mass
• Mass number


  The total number of protons and neutrons in the nucleus of an atom
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Isotopes of an element are chemically identical but have different masses
• Relative atomic mass (RAM) is the mean mass of an atom of an element compared to carbon-12, taking into account all the isotopes and their abundances