How We Know What We Can’t See Looks Like Day 4 Average Atomic Mass Atom’s Story How We Know What We Can’t See Looks Like Day 4 Average Atomic Mass

Relative masses on the P. Table are weighted averages of the isotopes. Atoms of the same element (they have the same number of protons) that have different masses because they have different numbers of neutrons. C C 13 C 14 C 11 12 Carbon – 12 makes up the greatest % of carbon in the universe MASS # 12 C 6 ATOMIC # Relative masses on the P. Table are weighted averages of the isotopes.

Composition of the nucleus Atomic Masses Atomic mass is the average of all the naturally isotopes of that element. Isotope Symbol Composition of the nucleus % in nature Carbon-12 12C 6 protons 6 neutrons 98.88% Carbon-13 13C 7 neutrons 1.11% Carbon-14 14C 8 neutrons <0.01% Average Atomic Mass = Mass Number1 * %1 + Mass Number2 * %2 + … Average atomic Mass Carbon = 12 * .9888 + 13 * 0.0111 + 14 * 0.0001 Carbon = 12.011