1. 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

2. 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.

3. 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 * * *
Carbon =