SC3 - Atomic Structure

• Isotopes are atoms of the same element with the same number of protons but a different number of neutrons. They have the same atomic number but different mass numbers.
• Atoms are made up of 3 subatomic particles:

  • Protons - positively charged and have a relative mass of 1
  • Neutrons - neutral and have a relative mass of 1
  • Electrons - negatively charged and have a relative mass if 1/1835 (negligible)
• The nucleus of an atom contains protons and neutrons so is positively charged and where most of the mass is concentrated.
• Atoms are neutral as they have the same number of protons and electrons.
• The mass number of an atom is the number of protons and neutrons in the nucleus.
• The atomic number of an atom is the number of protons in the nucleus of an atom.
• The relative atomic mass of an element is its average mass of 1 atom of all its isotopes.
• Relative Atomic Mass (Ar) = (Isotope 1 abundance X Isotope 1 mass) + (Isotope 2 abundance X Isotope 2 Mass) / Sum of abundances