CHEM 1127Q Lecture Notes - Lecture 3: Natural Abundance, Unified Atomic Mass Unit, Mass Number

• School: UConn
• Department: Chemistry
• Course: CHEM 1127Q
• Professor: Cady

Document Summary

Mass number is the number of protons plus the number of electrons. The bottom number is the amount of protons, top number is the mass number. (ie) 57fe has 26 protons, (doesn"t change) 31 neutrons (57-26) and because theres no charge the amount of electrons is equal to the number of protons. Isotopes are atoms with the same number of protons but a different number of neutrons. 12c is . 989323 of all carbon or 98. 93% We can tell where things come from depending on their isotopes. Mass numbers are always whole numbers but the mass on the periodic table is a decimal. The mass on the periodic table is the average mass, you calculate it from the mass number of all of the isotopes and their natural abundance. Atomic mass = (fraction of isotope 1 x mass of isotope 1) + (fraction of isotope 2 x mass of isotope 2) Remember it"s the fraction of the isotope 1.