Stoichiometry, Molecular Masses, and the Mole Concept

Vocabulary flashcards generated from lecture material on molecular mass, chemical formulas, Avogadro's number, molar mass conversions, mass percentages, and empirical/molecular formulas.

Molecular Mass

The sum of the atomic masses of the atoms in a molecule, expressed in atomic mass units ($amu$).

Formula Mass

The mass of a formula unit of an ionic compound, calculated by summing the atomic masses of its constituent atoms in atomic mass units ($amu$).

Mole (mol)

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

Avogadro's Number ($N_A$)

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

Molar Mass ($M$)

The mass of one mole of a substance's entities (atoms, molecules, or formula units), expressed in $g\,mol^{-1}$.

Empirical Formula

The simplest chemical formula for a compound that shows the lowest whole-number ratio of moles of each element present.

Molecular Formula

A chemical formula that shows the actual number of atoms of each element in a single molecule of a compound.

Structural Formula

A chemical representation that shows the relative placement and covalent connections between atoms in a molecule.

Mass Percent (Mass %)

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

Ball-and-stick Model

A 3D molecular depiction representing atoms as spheres and bonds as rods, displaying structural geometry such as the $104.5^\circ$ bond angle in water.

Space-filling Model

A 3D molecular model showing the relative sizes of atoms and how their electron clouds overlap in a molecule.

Binary Ionic vs. Binary Covalent Molecular Depictions

Representation (a) shows the continuous three-dimensional crystal lattice of sodium fluoride ($NaF$), an ionic compound, while representation (b) shows individual discrete molecules of nitrogen trifluoride ($NF_3$), a covalent compound.

Mass-Mole-Number Relationships for Elements

A roadmap where mass ($g$) is divided by molar mass ($M$) to yield amount ($mol$), which is then multiplied by Avogadro's number ($N_A$) to find the total number of atoms or molecules.

Ammonium Nitrate

A common agricultural fertilizer compound with the chemical formula $(NH_4)_2CO_3$ or $NH_4NO_3$, having a molar mass of $80.05\,g\,mol^{-1}$ and containing $35.00\,\text{mass \% } N$.

Lactic Acid

A muscle-soreness compound with a molar mass of $90.08\,g\,mol^{-1}$, an empirical formula of $CH_2O$, and a molecular formula of $C_3H_6O_3$.

Tetraphosphorus Trisulfide

A binary compound with the molecular formula $P_4S_3$ and a molecular mass of $220.06\,amu$.