How We Know What We Can’t See Looks Like

Day 4 Average Atomic Mass

IsotopesAtoms of the same element (they have the same

number of protons) that have different masses because they have different numbers of neutrons.

C C C C11 12 13 14

C12

6

Carbon – 12 makes up the greatest % of carbon in the universe

MASS #

ATOMIC #

Relative masses on the P. Table are weighted averages of the isotopes.

Atomic Masses

Isotope Symbol Composition of the nucleus

% in nature

Carbon-12

12C 6 protons6 neutrons

98.88%

Carbon-13

13C 6 protons7 neutrons

1.11%

Carbon-14

14C 6 protons8 neutrons

<0.01%

Atomic mass is the average of all the naturally isotopes of that element.

Carbon = 12.011

Average Atomic Mass = Mass Number1 * %1 + Mass Number2 * %2 + …

Average atomic Mass Carbon = 12 * .9888 + 13 * 0.0111 + 14 * 0.0001