Each element has a unique # of protons. So…EVERY SINGLE ATOM of that element MUST HAVE the SAME number of protons, ALWAYS! This is the reason why each element has a unique Atomic Number that never changes! Isotopes are atoms with the same # of protons (making them the SAME ELEMENT), but have a different # of neutrons. Having different # of neutrons for the same element means that the isotopes will have different mass numbers, too! There are 3 isotopes of oxygen: 8 8 8 O8 O9 O10 neutronsOxygen neutronsOxygen neutronsOxygen ALL oxygen16 isotopes 17have an atomic 18# of 8, so they all have 8 protons! How many protons does each isotope have? How many neutrons does each isotope have? There are 3 isotopes of carbon: 6 6 6 C6 C7 C8 neutronsCarbon neutronsCarbon neutronsCarbon ALL carbon12 isotopes 13have an atomic #14 of 6, so they all have 6 protons! How many protons does each isotope have? How many neutrons does each isotope have? Atomic Masses on the periodic table are normally decimals. WHY?? Atomic Masses are decimals because it is an AVERAGE mass of all of the element’s isotopes. Some isotopes are more common than others, so this is a weighted average. 5 So the Mass # from the periodic table is B always closest to the most common Boron isotope’s mass. 10.81 In the universe, there are MUCH more carbon-12 atoms that exist than carbon-13 and carbon-14 atoms. 6 C Carbon- 12 Carbon 12.01 When you find the weighted average of the masses of the carbon isotopes, the average will be closest to 12! The Atomic Mass of calcium is 40.08. 20 20 20 20 Ca Ca Ca Ca Calcium Calcium Calcium Calcium 40 42 43 44 Which one is the most common calcium isotope? This is because 40.08 rounded to a whole # is closest to calcium-40! The Atomic Mass of lithium is 6.94. 3 3 3 3 Li Li Li Li Lithium Lithium Lithium Lithium 5 6 7 8 Which one is the most common lithium isotope? This is because 6.94 rounded to a whole # is closest to lithium-7! • Hyphen Notation: • Element name – Mass # • Ex: Carbon – 14 • Nuclear Notation: Mass # Ex: 14 Atomic # X 6c Element Symbol.