Stoichiometry, Molecular Masses, and the Mole

Vocabulary flashcards reviewing fundamental stoichiometry concepts including molecular mass, Avogadro's number, molar mass, mass percent, and chemical formula interconversions.

Molecular mass

The sum of the atomic masses of the atoms in a molecule, calculated using values from the periodic table.

Formula mass

The mass of a formula unit of an ionic compound, calculated as the sum of its atomic masses because ionic compounds do not consist of discrete molecules.

Water representations and models

Methods of representing a water molecule, including its molecular formula ($H_2O$), structural formulas ($H-O-H$), ball-and-stick model ($104.5^\text{o}$ bond angle), and space-filling model.

Mole

The amount of a substance that contains the same number of entities as there are atoms in exactly $12\text{ g}$ of carbon-12.

Avogadro's number

The number of chemical entities contained in one mole of a substance, equal to $6.022 \times 10^{23}$ entities.

Chemical entities

The structural units counted in mole conversions, which can include atoms, ions, molecules, formula units, or electrons.

Molar mass

The mass in grams of one mole of a substance's entities, expressed in units of $\text{g/mol}$.

Monatomic element molar mass

The molar mass of an element consisting of single uncombined atoms, which is numerically equal to its atomic mass in atomic mass units ($\text{amu}$).

Mass-mole conversion formula

The calculation used to find mass in grams from amount in moles: $\text{Mass (g)} = n \times \text{Molar Mass}$, where $n$ is the amount in moles.

Mole-entity conversion formula

The calculation used to find the total number of particles: $\text{Number of entities} = n \times N_A$, where $N_A$ is Avogadro's number.

Mass percent

The percentage by mass of an element $X$ in a compound: $\text{Mass}\text{\%} = \frac{\text{moles of } X \text{ in formula} \times \text{molar mass of } X}{\text{mass of } 1\text{ mol of compound}} \times 100\text{\%}$.

Mass fraction

The ratio of the mass of a specific element in one mole of a compound to the total mass of one mole of that compound.

Tetraphosphorous trisulfide

A compound with the chemical formula $P_4S_3$ and a molecular mass of $220.06\text{ amu}$.

Ammonium nitrate

An ionic compound with the chemical formula $NH_4NO_3$ and a formula mass of $80.05\text{ amu}$, commonly used as a nitrogen-rich fertilizer.

Binary molecular depictions (a) and (b)

Microscopic representations illustrating (a) sodium fluoride ($NaF$), an ionic lattice with a $1:1$ ratio of $Na^+$ to $F^-$ ($41.99\text{ amu}$), and (b) nitrogen trifluoride ($NF_3$), a covalent compound with a $1:3$ ratio of $N$ to $F$ ($71.01\text{ amu}$).

Mass-mole-number relationships for elements

A conversion flow diagram showing how amount in moles ($n$) connects mass in grams to the total number of atoms or molecules using molar mass ($\text{Molar Mass}$) and Avogadro's number ($N_A$).

Amount-mass-number relationships for compounds

A roadmap showing relationships and conversions between compound mass, amount of compound in moles, constituent elements in moles, and total molecules or formula units.