Unit 1: Chemical Thinking - Distinguishing Substances, Modeling Matter, Analyzing Particles, and Determining Composition

Flashcards covering key vocabulary, definitions, definitions of properties, chemical classification, thermodynamic models, and compositional analysis techniques from Unit 1.

Mixture

A system containing two or more pure substances that can be either homogeneous or heterogeneous in composition.

Pure Substance

A sample of matter that possesses a constant chemical composition throughout.

Extensive Property

A physical or chemical property that depends on the amount of substance present, doubling when two identical samples are combined (e.g., mass, length).

Intensive Property

A property that does not depend on the amount of substance present, remaining unchanged when two identical samples are combined (e.g., density, boiling point).

Differentiating Characteristic

An intensive and specific property unique to a substance that is used to detect, identify, separate, or quantify it.

Volatility

A measure of how easily a liquid converts into a gas; highly volatile liquids evaporate readily and exhibit high vapor pressures.

Boiling Point

The temperature at which a liquid's vapor pressure equals the prevailing atmospheric pressure.

Filtration

A physical separation method used to separate solid particles from liquids based on differences in particle size.

Fractional Distillation

A separation process that isolates components of a liquid or liquefied mixture based on differences in their boiling points.

Phase Diagram

A pressure-temperature graph defining the specific conditions under which solid, liquid, and gas phases exist, coexist, or undergo phase transitions.

Particulate Model of Matter

A model assuming that any macroscopic sample is composed of a large number of very small particles (typically nanometer size) moving constantly and randomly through empty space.

Temperature (Particulate Definition)

A macroscopic measure of the average kinetic energy per particle in a system, expressed as $\langle K \rangle = \frac{1}{2} m \langle v^2 \rangle$.

Boltzmann Constant ($k_B$)

The fundamental physical constant in the ideal gas expression $P = k_B \frac{N T}{V}$, equal to $1.380 \times 10^{-23}\,J\,K^{-1}$.

Potential Energy ($E_p$)

Energy stored in a system of interacting particles due to intermolecular forces, whose value changes as particles approach or separate from each other.

PEC Diagram

A graphical representation comparing Potential Energy ($E_p$) and the Number of Configurations of particles to predict phase transitions and state stability under varying temperature and pressure.

Elementary Substance

The simplest form of matter in nature, composed of identical particles made of free or bonded atoms of the exact same chemical type.

Chemical Compound

A substance composed of identical particles containing bonded atoms of two or more different chemical elements.

Molecular Compound

A class of compounds composed of discrete molecules containing fixed numbers and arrangements of bonded atoms.

Ionic Compound

A chemical compound composed of cations and anions held in extended three-dimensional lattice networks rather than individual molecules.

Formula Unit

The chemical formula of an ionic compound that establishes the lowest whole-number ratio of cations to anions in the crystal lattice.

Avogadro's Number ($N_A$)

The proportionality constant representing the number of particles in one mole of any substance, defined as $6.022 \times 10^{23}\,particles$.

Mole ($n$)

The SI unit for amount of substance, containing exactly Avogadro's number ($6.022 \times 10^{23}$) of specified particles.

Molar Mass ($M$)

The mass of one mole of a substance expressed in units of $g\,mol^{-1}$, equal in magnitude to the relative mass of its constituent particles.

Mass Spectrometry

An analytical technique that vaporizes particles, converts them into charged ions, accelerates them, and separates them by their mass-to-charge ratio ($m/z$) using a magnetic field.

Atomic Number ($Z$)

The number of protons in the nucleus of an atom, which characterizes each distinct chemical element.

Mass Number ($A$)

The total count of protons and neutrons within the nucleus of an atom ($A = \# p^+ + \# n^0$).

Isotopes

Atoms of the same chemical element that possess the same number of protons (atomic number $Z$) but different numbers of neutrons (mass number $A$).

Molecular Ion Peak

The peak in a mass spectrum that corresponds to the unfragmented ionized parent molecule, indicating its molecular mass.

Major Peak

The tallest peak in a mass spectrum, normalized to 100% relative abundance, representing the most abundant ion formed.

Fragment Peaks

Peaks in a mass spectrum with smaller mass-to-charge ratios ($m/z$) than the molecular ion peak, produced when parent molecules break apart during ionization.

Empirical Formula

The chemical formula representing the simplest whole-number ratio of atoms of each element present in a compound.

Molecular Formula

The chemical formula detailing the actual exact number of atoms of each element present in a single molecule of a compound.