UAE TLS Chemistry Test key terms

The amount of a substance that contains exactly 6.022 × 10^23 representative particles, such as atoms, molecules, or ions. It links the mass of a sample to the number of particles it contains.

The number of particles in one mole of a substance, approximately 6.022 × 10^23 per mole. It allows conversion between counted particles and measurable amounts of substance.

The mass of one mole of a substance, expressed in grams per mole. Numerically it equals the sum of atomic masses of all atoms in the formula unit.

The reactant that is fully consumed first in a chemical reaction and therefore determines the maximum amount of product that can form. Other reactants remain in excess.

The quantitative relationship between amounts of reactants and products in a balanced chemical equation. It uses mole ratios from coefficients to predict masses or volumes involved.

The simplest whole-number ratio of atoms of each element present in a compound. It is derived from percentage composition or experimental mass data.

The maximum mass of product predicted from a balanced equation when the limiting reactant is completely consumed. It serves as the reference for calculating percentage yield.

An atom of the same element that has a different number of neutrons and therefore a different mass number. Isotopes share chemical properties but differ in mass and nuclear stability.

The number of protons in the nucleus of an atom, which uniquely identifies the element. In a neutral atom it also equals the number of electrons.

The total number of protons and neutrons in the nucleus of an atom. It is written as a superscript before the element symbol and distinguishes isotopes of the same element.

The minimum energy required to remove the most loosely bound electron from a gaseous atom or ion. It generally increases across a period and decreases down a group.

A measure of the size of an atom, usually taken as half the distance between nuclei of two bonded atoms of the same element. It decreases across a period and increases down a group.

A measure of how strongly an atom attracts shared electrons in a chemical bond. Large differences between bonded atoms lead to polar or ionic bonding.

The electrostatic attraction between oppositely charged ions formed when electrons are transferred from one atom to another. It typically occurs between metals and nonmetals and creates lattice structures.

A chemical bond formed when two atoms share one or more pairs of electrons. It is typical between nonmetals and can be single, double, or triple.

A covalent bond in which shared electrons are unequally attracted by the two atoms, creating partial positive and partial negative charges. It arises from a moderate difference in electronegativity.

A relatively strong intermolecular attraction between a hydrogen atom bonded to oxygen, nitrogen, or fluorine and a lone pair on a nearby electronegative atom. It explains many unusual properties of water.

Attractive forces between separate molecules, including dispersion forces, dipole-dipole interactions, and hydrogen bonds. They are weaker than covalent bonds but determine boiling points and physical states.

A model stating that electron pairs around a central atom arrange themselves as far apart as possible to minimize repulsion. It predicts molecular shapes such as linear, tetrahedral, and trigonal planar.

The equation PV = nRT relating pressure, volume, amount in moles, and absolute temperature of a gas. It assumes negligible particle volume and no intermolecular attractions.

A model describing gases as particles in constant random motion that collide elastically and exert pressure through collisions with container walls. It explains temperature as average kinetic energy.

The pressure that one component of a gas mixture would exert if it alone occupied the whole container. The total pressure is the sum of all partial pressures.

The pressure exerted by a vapor in equilibrium with its liquid or solid at a given temperature. It increases with temperature and with weaker intermolecular forces.

The temperature at which the vapor pressure of a liquid equals the external pressure applied to it, allowing boiling throughout the liquid. It rises with stronger intermolecular forces.

A thermodynamic quantity representing the heat content of a system at constant pressure. The change in enthalpy measures heat absorbed or released during a reaction.

A principle stating that the total enthalpy change of a reaction is the same regardless of the pathway taken, because enthalpy is a state function. It allows calculation of unknown enthalpy changes from known ones.

The minimum energy that colliding particles must possess for a chemical reaction to occur. It determines the reaction rate and is lowered by a catalyst.

A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy, without being consumed. It does not change the position of equilibrium.

A rule stating that when a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts to counteract the change. It predicts the direction of equilibrium adjustment.

The ratio of product concentrations to reactant concentrations, each raised to its coefficient power, at equilibrium for a given temperature. Its magnitude indicates whether products or reactants are favored.

A logarithmic scale from 0 to 14 measuring hydrogen ion concentration, where pH = -log[H+]. Values below 7 are acidic, 7 is neutral, and above 7 are basic.

A substance that donates protons or accepts electron pairs, and which increases hydrogen ion concentration in water. Acids neutralize bases to form salt and water.

A substance that accepts protons or donates electron pairs, and which increases hydroxide ion concentration in water. Bases neutralize acids to form salt and water.

A solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists large pH changes on addition of small amounts of acid or base.

The loss of electrons by a substance during a redox reaction, accompanied by an increase in oxidation state. It is always paired with reduction.

The gain of electrons by a substance during a redox reaction, accompanied by a decrease in oxidation state. It is always paired with oxidation.

A number assigned to an atom in a compound that reflects its apparent electron loss or gain relative to the free element. It helps identify oxidation and reduction in reactions.

The process of driving a nonspontaneous chemical reaction by passing an electric current through an electrolyte. It is used for electroplating and extracting reactive metals.

A specific group of atoms within a molecule that gives the compound characteristic chemical properties and reactivity, such as hydroxyl, carboxyl, or carbonyl groups.

One of two or more compounds that have the same molecular formula but different arrangements of atoms and therefore different properties. Structural isomers differ in connectivity.

A family of organic compounds with the same functional group and similar chemical properties, in which successive members differ by one CH2 unit.

A quantitative procedure in which a solution of known concentration is added gradually to a measured volume of another solution until the reaction reaches its endpoint, allowing concentration to be calculated.

The point in a titration at which the indicator changes color, signaling that the reaction is complete. It should closely match the equivalence point for accurate results.

Information obtained through direct observation or measurement rather than reasoning alone. In chemistry it supports or refutes hypotheses about matter and reactions.