Bagrut Chemistry flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Aufbau principle

Electrons fill orbitals in order of increasing n+ℓ energy; for equal n+ℓ, the lower n fills first, giving configurations such as 1s²2s²2p⁶3s².

Hund's rule

Within a subshell, electrons occupy separate orbitals with parallel spins before pairing; this maximizes total spin and minimizes electron–electron repulsion.

Effective nuclear charge

The net positive charge experienced by an electron after shielding by other electrons; it increases across a period, shrinking atomic radius and raising ionization energy.

VSEPR theory

Electron domains around a central atom repel and arrange to minimize repulsion; lone pairs repel more strongly than bonds, reducing bond angles from ideal values.

Hydrogen bond

A strong dipole–dipole attraction between H bonded to N, O, or F and a lone pair on a nearby N, O, or F atom; it raises boiling points and structures water and ice.

Hybridization

Mixing of atomic orbitals to form equivalent hybrid orbitals; steric number 2 gives sp, 3 gives sp², and 4 gives sp³ geometry.

Limiting reagent

The reactant that is completely consumed first, determined by dividing each reactant's moles by its stoichiometric coefficient; it sets the maximum product yield.

Molarity

Concentration expressed as moles of solute per liter of solution, c = n/V; dilutions obey c₁V₁ = c₂V₂ when no reaction occurs.

Empirical formula

The simplest whole-number ratio of atoms in a compound, found by dividing mass percentages by atomic masses and reducing to the smallest integer ratio.

Ideal gas law

PV = nRT relates pressure, volume, moles, and absolute temperature; R = 0.08206 L·atm/(mol·K), and the gas is most ideal at low P and high T.

Dalton's law

The total pressure of a nonreacting gas mixture equals the sum of the partial pressures; each partial pressure is the mole fraction times the total pressure.

Critical point

The temperature and pressure above which a substance cannot be liquefied by pressure alone; the liquid and gas phases become indistinguishable at this point.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partially offsets the disturbance.

Reaction quotient Q

The same ratio as the equilibrium constant but using current concentrations; Q < K shifts forward, Q > K shifts reverse, and Q = K means equilibrium.

Equilibrium constant K

The ratio of product to reactant activities at equilibrium, each raised to its stoichiometric coefficient; it depends only on temperature, not on initial concentrations.

Henderson–Hasselbalch equation

pH = pKa + log([A⁻]/[HA]) gives the pH of a buffer from the weak acid's pKa and the conjugate base-to-acid concentration ratio.

Buffer solution

A mixture of a weak acid and its conjugate base (or weak base and conjugate acid) that resists pH change on adding small amounts of strong acid or base.

Solubility product Ksp

The equilibrium constant for dissolving a sparingly soluble salt, equal to the product of ion concentrations raised to their stoichiometric coefficients; a precipitate forms when Q > Ksp.

Hess's law

The enthalpy change of a reaction is independent of the pathway; summing the ΔH values of steps that add to the target reaction gives its ΔH.

Standard enthalpy of formation

The enthalpy change when one mole of a compound forms from its elements in their standard states; elements in standard states have ΔH°f = 0.

Gibbs free energy

ΔG = ΔH − TΔS determines spontaneity: ΔG < 0 means spontaneous, ΔG = 0 means equilibrium, and ΔG° = −RT ln K.

Oxidation number

A bookkeeping charge assigned to an atom assuming ionic bonding; oxidation is an increase and reduction a decrease in oxidation number.

Standard cell potential

E°cell = E°cathode − E°anode using reduction potentials; a positive value means the cell reaction is spontaneous with ΔG° = −nFE°cell.

Faraday's law of electrolysis

The amount of substance deposited or dissolved is proportional to the charge passed; moles of electrons equal It/F, with F ≈ 96,485 C/mol.

Arrhenius equation

k = A·e^(−Ea/RT) shows that the rate constant rises with temperature and falls with activation energy; ln k vs 1/T has slope −Ea/R.

Rate-determining step

The slowest elementary step in a mechanism; it controls the overall reaction rate, and its reactants appear in the overall rate law.

Catalyst

A substance that speeds a reaction by providing a lower-activation-energy pathway without being consumed; it does not change ΔH or the equilibrium constant.

Markovnikov's rule

In addition of HX to an alkene, the hydrogen adds to the carbon bearing more hydrogens, and the halogen adds to the more substituted carbon.

Functional group

An atom or group of atoms that gives a molecule its characteristic chemical reactivity, such as –OH in alcohols or –COOH in carboxylic acids.

Structural isomer

Molecules with the same molecular formula but different connectivity of atoms, giving different physical and chemical properties.

Chiral carbon

A carbon bonded to four different groups; it makes the molecule non-superimposable on its mirror image and produces enantiomers.

Esterification

The reversible, acid-catalyzed reaction of a carboxylic acid with an alcohol to form an ester and water; hydrolysis reverses it.

Half-life

The time required for half of a reactant to be consumed; for first-order reactions t₁/₂ = 0.693/k and is independent of initial concentration.