The atomic mass of a chemical element is the number of protons + number of neutrons in each atom of that element—electrons are ignored. Examples The atomic mass of hydrogen (H) is 1 (1 proton) and that of helium (He) is 4 (2 protons + 2 neutrons). The gram atomic mass of a chemical element is the atomic mass of that element in grams. Example The gram atomic mass of H is 1 gram and that for He is 4 grams.

Astounding Fact There are approximately 6 x 1023 atoms in the gram atomic mass of every known chemical element. Examples There are 6 x 1023 atoms in 1 gram of H and in 4 grams of He. Hence, there are 12 x 1023 atoms, or 1.2 x 1024 atoms, in 2 grams of H and in 8 grams of He.

Standard carbon is Carbon 12, abbreviated C-12. Its atomic number is 12 (6 protons and 6 neutrons) and its gram atomic mass is therefore 12 grams.

How many atoms are there in 96 grams of C-12? (Read the exponents carefully.)

(a) 1.2 x 1024 atoms (b) 12 x 1023 atoms (c) 4.8 x 1023 atoms

(d) 4.8 x 1024 atoms (e) 96 x 1024 atoms (f) none of the above