Armenia Chemistry Unified Exam key terms

A region of space around a nucleus where the probability of finding an electron is high, described by quantum numbers and holding at most two electrons of opposite spin.

One of a set of integers or half-integers (principal, azimuthal, magnetic, spin) that specifies the energy, shape, orientation, and spin state of an electron in an atom.

The arrangement of electrons among the orbitals of an atom or ion, usually written in order of increasing energy and governed by the Aufbau principle and Hund's rule.

The rule stating that no two electrons in the same atom can share all four quantum numbers, so one orbital holds at most two electrons with paired spins.

The statement that properties of the elements vary periodically with increasing atomic number because outer electron configurations repeat in a regular pattern.

The minimum energy needed to remove one electron from a gaseous atom or ion; it generally increases across a period and decreases down a group.

A measure of the effective size of an atom, usually half the distance between nuclei of bonded or touching atoms; it decreases across a period and increases down a group.

A relative measure of how strongly an atom in a bond attracts shared electrons; values rise across a period and fall down a group, with fluorine highest.

The electrostatic attraction between oppositely charged ions formed when electrons are transferred from a metal to a nonmetal with a large electronegativity difference.

A bond formed when two atoms share one or more pairs of electrons, typically between nonmetals with similar electronegativities.

A covalent bond in which shared electrons are unequally attracted by the two atoms, producing partial positive and negative charges and often a molecular dipole.

A strong intermolecular attraction between a hydrogen atom bonded to N, O, or F and a lone pair on a nearby electronegative atom; it raises boiling points and stabilizes water structure.

The regular three-dimensional array of ions, atoms, or molecules held in fixed positions by attractive forces, giving crystalline solids characteristic shapes and high melting points.

The existence of an element in two or more structural forms in the same physical state, such as diamond and graphite for carbon or dioxygen and ozone for oxygen.

A hydroxide that reacts with both acids and bases to form salts, typical of certain metals such as aluminum and zinc.

The amount of substance containing as many elementary entities as there are atoms in 12 g of carbon-12, equal to Avogadro's number, about 6.02 x 10^23.

The mass of one mole of a substance in grams per mole, numerically equal to its relative molecular mass.

The volume occupied by one mole of any gas under specified conditions, approximately 22.4 L at standard temperature and pressure for an ideal gas.

The reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can form.

The actual mass of product obtained expressed as a percentage of the theoretical mass calculated from stoichiometry.

The change in concentration of a reactant or product per unit time; it increases with temperature, concentration, surface area, and the presence of a catalyst.

The minimum energy that colliding particles must possess for a reaction to occur, corresponding to the energy barrier between reactants and products.

A substance that speeds up a reaction by providing an alternative pathway with lower activation energy while remaining chemically unchanged at the end.

The state of a reversible reaction in which forward and reverse rates are equal, so concentrations of reactants and products remain constant over time.

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

The heat exchanged with the surroundings at constant pressure during a chemical reaction; it is negative for exothermic and positive for endothermic processes.

The principle that the total enthalpy change of a reaction is the same regardless of the route taken, allowing calculation from known formation or combustion enthalpies.

The process in which solvent molecules surround and interact with dissolved particles, stabilizing them in solution and often releasing or absorbing heat.

The amount of solute in moles divided by the volume of solution in liters, expressed in moles per liter (mol/L).

A substance that conducts electric current when dissolved or molten because it dissociates into mobile ions; strong electrolytes ionize completely, weak ones only partly.

A logarithmic scale of hydrogen ion activity, defined as the negative base-10 logarithm of the hydrogen ion concentration; values below 7 are acidic.

The reaction between an acid and a base producing a salt and water, in which hydrogen ions and hydroxide ions combine.

A quantitative procedure in which a solution of known concentration is added from a burette to a measured volume of analyte until an indicator signals the equivalence point.

The loss of electrons by a species, accompanied by an increase in oxidation state; it occurs at the anode in an electrochemical cell.

The gain of electrons by a species, accompanied by a decrease in oxidation state; it occurs at the cathode in an electrochemical cell.

The use of an external electric current to drive a nonspontaneous redox reaction in an electrolyte, producing chemical change at the electrodes.

A family of organic compounds with the same functional group and general formula, whose members differ by one CH2 unit and show gradually changing properties.

An atom or group of atoms within a molecule that determines its characteristic chemical reactions, such as hydroxyl, carboxyl, or amino groups.

The occurrence of compounds with the same molecular formula but different arrangements of atoms, giving distinct structures and properties.