Armenia Chemistry Unified Exam flashcards
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- Isotopes
- Atoms of the same element with the same number of protons (atomic number) but different numbers of neutrons, thus different mass numbers and physical properties.
- Hund's rule
- In a subshell, electrons fill degenerate orbitals singly with parallel spins before any orbital receives a second electron, minimizing electron repulsion.
- Effective nuclear charge
- The net positive charge experienced by an electron, equal to the actual nuclear charge minus the shielding by inner electrons; increases across a period.
- VSEPR theory
- Valence Shell Electron Pair Repulsion model predicts molecular geometry: electron domains around a central atom arrange to minimize repulsion, with lone pairs occupying more space than bonding pairs.
- Hydrogen bonding
- A strong intermolecular force between a hydrogen atom bonded to N, O, or F and a lone pair on another electronegative atom; explains water's high boiling point.
- Hybridization
- The mixing of atomic orbitals to form new equivalent hybrid orbitals (sp, sp², sp³) that determine molecular geometry and bonding.
- Ionization energy
- The minimum energy required to remove an electron from a gaseous atom or ion; generally increases across a period and decreases down a group.
- Amphoteric oxide
- An oxide that reacts with both acids and bases to form salts and water, such as Al₂O₃ and ZnO.
- Halogen displacement
- A more reactive halogen displaces a less reactive halide ion from solution; reactivity order is F₂ > Cl₂ > Br₂ > I₂.
- Ligand
- An ion or molecule that donates one or more electron pairs to a central metal ion to form a coordinate covalent bond in a complex.
- Crystal field splitting
- The energy difference (Δ) between lower and higher energy d orbitals when ligands approach a metal ion; determines color and magnetic properties of complexes.
- Coordination number
- The number of donor atoms directly bonded to the central metal ion in a coordination compound.
- Limiting reactant
- The reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can be formed.
- Molar mass
- The mass of one mole of a substance in grams per mole; numerically equal to the sum of atomic masses of all atoms in the formula.
- Empirical formula
- The simplest whole-number ratio of atoms of each element in a compound, derived from percent composition or experimental mass data.
- Rate law
- An equation relating reaction rate to reactant concentrations raised to experimentally determined powers (orders), with a rate constant k.
- Activation energy
- The minimum energy that colliding molecules must possess for a chemical reaction to occur; lowered by a catalyst.
- First-order half-life
- For a first-order reaction, the time required for reactant concentration to halve; t₁/₂ = 0.693/k, independent of initial concentration.
- Hess's law
- The enthalpy change of a reaction is the same whether it occurs in one step or several steps, allowing calculation from known enthalpy changes.
- Gibbs free energy
- ΔG = ΔH − TΔS; a negative ΔG indicates a spontaneous process at constant temperature and pressure, positive nonspontaneous, zero equilibrium.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts to counteract the change and restore equilibrium.
- Molality
- The number of moles of solute per kilogram of solvent; unlike molarity, it is independent of temperature because it uses mass.
- Colligative properties
- Properties of solutions that depend on the number of solute particles, not their identity: vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure.
- Dilution equation
- M₁V₁ = M₂V₂; the number of moles of solute remains constant when a solution is diluted with solvent.
- Brønsted–Lowry acid
- A substance that donates a proton (H⁺) to another substance; its conjugate base is formed after losing the proton.
- pH
- The negative base-10 logarithm of the hydrogen ion concentration: pH = −log[H⁺]; at 25 °C, pH + pOH = 14.
- Buffer solution
- A solution containing a weak acid and its conjugate base (or weak base and conjugate acid) that resists significant pH changes upon addition of small amounts of acid or base.
- Oxidation
- The loss of electrons by a substance, resulting in an increase in its oxidation number; occurs at the anode in electrochemical cells.
- Standard cell potential
- E°_cell = E°_cathode − E°_anode; a positive value indicates a spontaneous redox reaction under standard conditions.
- Faraday's law
- The mass of substance deposited or dissolved at an electrode is proportional to the quantity of electric charge passed: m = (M·I·t)/(n·F).
- Functional group
- A specific group of atoms within a molecule that determines its characteristic chemical properties and reactivity, such as –OH, –CHO, –COOH, –NH₂.
- Esterification
- The acid-catalyzed reaction of a carboxylic acid with an alcohol to form an ester and water, often reversible.
- Titration endpoint
- The point in a titration at which the indicator changes color, signaling that the amount of titrant added is stoichiometrically equivalent to the analyte.
- Significant figures
- The digits in a measurement that carry meaningful information about its precision; rules govern rounding in calculations involving measured quantities.