1.9-1.10 Average Atomic Mass, The Mole Concept and Molar Mass

isotopes

atoms that are different forms of the same chemical element with the same number of protons but different number of neutrons (thus slightly different masses)

mass number (A)

number of protons+neutrons

natural abundance

the relative amount of an isotope in a naturally occurring sample of an element; usually given as percentages

atomic mass

a weighted average of the masses of the isotopes that compose that element
the number underneath the symbol

how to calculate the average atomic mass of an element in general

average atomic mass = [(abundance %)(mass)]+[(abundance %)(mass)]
all percent abundances add up to 100%

the Mole (mol)

unit of amount

avogadro’s number (N_A)

6.022×10²³ atoms, molecules, units, etc… can be used as a conversation factor (number of entities to moles of entities)

Molar Mass of an element

the mass of one mole of a substance
equal to atomic mass
can be used as a conversion factor (mass to moles)

grams to moles conversion

mass (g) / molar mass (g/mol)

grams to atoms

mass (g) / molar mass (g/mol) *6.022×10²³ atoms

symbolizing isotopes