AP Chemistry Unit 3: Intermolecular Forces, Solutions, and Spectroscopy

Vocabulary practice flashcards covering AP Chemistry Unit 3 lecture topics, including gas deviations, solution formation, representations of solutions, chromatography, distillation, spectroscopy regions, the photoelectric effect, and the Beer-Lambert Law.

Beer-Lambert Law

The law stating that the absorbance of a solution is directly proportional to the molar absorptivity constant, the path length, and the concentration, expressed by the equation $A = \varepsilon b c$.

Molar Absorptivity Constant ($\varepsilon$)

A constant describing how intensely a sample of molecules or ions absorbs light of a specific wavelength; mathematically equal to the slope of an absorbance versus concentration calibration plot, with units of $1/(\text{M}\cdot\text{cm})$.

Path Length ($b$)

The internal width of the cuvette holding the sample in a spectrophotometer through which light passes, with a standard value held constant at $1\,\text{cm}$.

Spectrophotometric Blank

A cuvette containing only the pure solvent (usually water) used to calibrate the spectrophotometer so that absorbance from the solvent is removed, analogous to using the tare button on a digital balance.

Complementary Colors in Spectroscopy

The wavelength relationship where a colored solution primarily absorbs light of its opposite complementary color; for example, a red solution absorbs green light in the range of $560-520\,\text{nm}$.

Photoelectric Effect

The emission of electrons from the surface of a metal when electromagnetic radiation of sufficient frequency strikes it, demonstrating both wave-like and particle-like behaviors of light.

Work Function (Binding Energy, $\Phi$)

The minimum energy required to remove an electron from a specific metal's surface, calculated by $\Phi = \frac{hc}{\lambda_{\text{MAX}}} = h\nu_0$.

Threshold Frequency ($\nu_0$)

The minimum frequency that incident light must possess to eject electrons from the surface of a metal in the photoelectric effect.

Threshold Wavelength ($\lambda_{\text{MAX}}$)

The longest wavelength of light capable of providing enough energy to eject an electron from a metal surface; any wave shorter than this threshold will eject electrons.

Photoelectric Current

The rate of emission of photoelectrons from a metal surface, which is directly proportional to the intensity of the incident light.

Planck's Constant ($h$)

A fundamental constant of proportionality relating the energy of a photon to its frequency ($E = h\nu$), with a value of $6.626 \times 10^{-34}\,\text{J}\cdot\text{s}$.

Microwave Rotational Spectroscopy

A spectroscopic technique utilizing microwave radiation, which interacts with the permanent dipoles of molecules to cause transitions in molecular rotational energy levels.

Infrared (IR) Vibrational Spectroscopy

A spectroscopic technique that measures molecular absorption, emission, or reflection to observe transitions in molecular vibrational energy levels and identify functional groups.

Ultraviolet-Visible (UV-Vis) Spectroscopy

A spectroscopic technique using radiation in the $\sim 50-700\,\text{nm}$ range to promote electrons from their ground state to higher-energy excited electronic states, commonly used to determine solution concentration.

Translational Motion

The movement of an entire molecule through space from one physical location to another.

Rotational Motion

The movement of a molecule spinning around its own center of mass in place.

Vibrational Motion

The internal movement of atoms within a molecule relative to one another, including stretching and bending modes.

Steps of Solution Formation

The thermodynamic three-step process: 1) solute particles separate (energy required), 2) solvent particles separate (energy required), and 3) solute and solvent particles come together (energy released).

Miscible

The property of two liquids that have the ability to mix together uniformly in all proportions without separating into distinct phases, such as vinegar and water.

Immiscible

The property of two liquids that cannot mix together and separate into distinct layers, such as oil and water.

Hydration

The process in which water molecules surround dissolved ions, orienting partially positive hydrogens toward negative anions and partially negative oxygens toward positive cations via ion-dipole interactions.

Retention Factor ($R_f$)

A characteristic value in chromatography calculated as the ratio of the distance traveled by a solute dye ($d_{\text{dye}}$) to the distance traveled by the solvent front ($d_{\text{solvent}}$).

Paper Chromatography

A separation method utilizing paper as the stationary phase and a liquid solvent as the mobile phase to separate components of a mixture based on differences in polarity and intermolecular forces.

Thin Layer Chromatography (TLC)

A chromatography technique where separation takes place on a thin layer of polar adsorbent (such as silica or alumina) adhered to a plastic sheet, frequently analyzed using UV light or ninhydrin spray for amino acids.

Column Chromatography

A preparative separation technique where a mixture is loaded at the top of a burette packed with a polar stationary phase (silica or alumina gel over steel wool) and eluted with a solvent, separating components by polarity rate.

Distillation

A physical separation technique that separates liquid mixture components based on differences in boiling points, vapor pressures, and intermolecular forces.

Fractional Distillation

A specialized distillation process utilizing a fractionating column (such as a Vigreux column) that enables multiple condensation and revaporization cycles to purify liquids with close boiling points.

Solution (Homogeneous Mixture)

A uniform solid, liquid, or gas mixture whose macroscopic properties do not vary by location, cannot be separated by filtration, and lacks particles large enough to scatter visible light.

Molarity ($M$)

The laboratory concentration unit defined as moles of solute divided by liters of solution ($M = \frac{n_{\text{solute}}}{L_{\text{solution}}}$).

Ion Concentration Dissociation Stoichiometry

The principle that ionic compound dissociation affects individual ion concentrations; for example, a $1\,\text{M}$ solution of $\text{CaCl}_2$ dissociates to give $1\,\text{M}\,\text{Ca}^{2+}$ and $2\,\text{M}\,\text{Cl}^-$.

Ideal Gas Law Deviation at High Pressure

The deviation from ideal gas behavior occurring at high pressures ($P > 5\,\text{atm}$) where gas particle volume occupies a significant fraction of the container and can no longer be ignored, requiring subtraction from total container volume.

Ideal Gas Law Deviation at Low Temperature

The deviation from ideal gas behavior occurring as temperature drops, causing gas particles to move slower and experience significant intermolecular attractions, leading to clumping and decreased container wall collisions.

Ion-Dipole Interaction

An intermolecular attraction between a fully charged ion and a polar molecule, with interaction energies typically ranging between $40-600\,\text{kJ/mol}$.

Ion-Induced Dipole Interaction

An intermolecular attraction between an ion and a nonpolar molecule whose electron cloud is distorted by the electric field of the ion, having typical interaction energies of $3-15\,\text{kJ/mol}$.

Dipole-Induced Dipole Interaction

An intermolecular attraction between a permanent dipole of a polar molecule and a temporary dipole induced in a nearby nonpolar species, with energies typically ranging from $2-10\,\text{kJ/mol}$.