Moles and Stoichiometry Lecture Notes

Vocabulary terms and fundamental definitions from the lecture on Moles and Stoichiometry, including isotopic mass, atomic mass, molecular mass, and the mole concept.

Isotopes

Atoms of the same element that have the same number of protons and electrons but a different number of neutrons, resulting in different masses but the same electronic configuration.

Relative Isotopic Mass

The mass of an isotope as compared to $\frac{1}{12}$ the mass of a Carbon-12 atom.

Carbon-12

The specific isotope of carbon used as a standard for calculations of relative mass in chemistry.

Relative Atomic Mass ($A_r$)

The average mass of an element's isotopes compared to $\frac{1}{12}$ the mass of a Carbon-12 atom, calculated using mass and percentage abundance.

Relative Molecular Mass ($M_r$)

The mass of a molecule as compared to $\frac{1}{12}$ the mass of a Carbon-12 atom, calculated by adding the relative atomic masses ($A_r$) of all atoms in one molecule.

Relative Formula Mass

The mass of a formula unit of an ionic compound as compared to $\frac{1}{12}$ the mass of a Carbon-12 atom, symbolized as $M_r$ and used for substances in an ionic lattice.

Formula Unit

The simplest ratio between ions in an ionic lattice, used to determine the mass of ionic compounds since they do not exist as simple molecules.

Mole

The amount of a substance that contains Avogadro's number of particles.

Avogadro's Number ($L$)

A constant value of $6.02 \times 10^{23}$ representing the number of particles in one mole, proposed by Amedeo Avogadro.

Molar Mass

The mass of one mole ($6.02 \times 10^{23}$ particles) of a substance, expressed in grams ($g$).

Calculation of Moles (by mass)

The formula defined as $\text{Moles (n)} = \frac{\text{Given mass (m)}}{\text{Molar mass (Mr)}}$.

Calculation of Moles (by particles)

The formula defined as $\text{Moles (n)} = \frac{\text{Number of Particles}}{\text{Avogadro's Number (L)}}$.

Number of Atoms in a Sample

A value determined by multiplying the number of particles in a sample by the number of atoms present in one particle.