AP Chem Vocab

Matter

Anything that occupies space and has mass; the physical material of the universe.

Chemical Change

Processes in which a substance is transformed into a chemically different substance; also called chemical reactions.

Physical Change

Changes in physical appearance (such as a phase change) that occur with no change in chemical composition.

Intensive Property

A property that does not depend on the amount of sample being examined, for example, density.

Extensive Property

A property that depends on the amount of sample considered; for example, mass or volume.

Physical Property

Properties that can be measured without changing the composition of a substance, for example, color and freezing point.

Chemical Property

Properties that describe the way a substance may change, or react, to form other substances.

Element

A substance that cannot be decomposed into simpler substances through chemical means.

Compound

A substance composed of two or more elements united chemically in definite proportions.

Mixture

A combination of two or more substances in which each substance retains its own chemical identity.

Pure Substance

Matter that has a fixed composition and distinct properties.

Homogeneous Mixture

A mixture in which the components are evenly distributed throughout, making it look the same everywhere.

Heterogeneous Mixture

A mixture in which the components are not evenly distributed, so different parts of the mixture look different.

Distillation

A separation process that depends on the different abilities of substances to form gases.

Filtration

A separation process used to remove solid particles from a liquid or gas by passing the mixture through a filter.

Paper Chromatography

Separate different substances in a mixture by moving them along a piece of paper with the help of a solvent.

John Dalton

Known for developing atomic theory.

J.J. Thomson

Known for discovering the electron and the structure of the atom.

Robert Millikan

Known for developing the oil-drop experiment (charge of an electron).

Henri Becquerel

Known for discovering radioactivity.

Ernest Rutherford

Known for discovering the nucleus.

James Chadwick

Known for discovering the neutron.

Atom

The smallest representative particle of an element. The almost infinitesimally small building blocks of matter.

Nucleus

The very small, very dense, positively charged portion of an atom; it is composed of protons and neutrons.

Atomic Number

The number of protons in the nucleus of an atom of an element.

Mass Number

The sum of the number of protons and neutrons in the nucleus of a particular atom.

Isotopes

Atoms of the same element containing different numbers of neutrons and therefore having different masses.

Atomic Mass Unit (amu)

A unit based on the value of exactly 1/12 of a Carbon-12 isotope.

Atomic Mass

The average mass of all the isotopes of an element.

Proton

A positively charged subatomic particle found in the nucleus of an atom.

Neutron

An electrically neutral particle found in the nucleus of an atom; it has approximately the same mass as a proton.

Electron

A negatively charged subatomic particle found outside the atomic nucleus; it is a part of all atoms.

Periodic Table

The arrangement of elements in order of increasing atomic number, with elements having similar properties placed in vertical columns.

Molecule

A chemical combination of two or more atoms.

Ionic Compound

A compound composed of cations and anions.

Ions

Electrically charged atom or group of atoms; can be positively or negatively charged, depending on whether electrons are lost (positive) or gained (negative) by the atoms.

Empirical Formula

A chemical formula that shows the kinds of atoms and their relative numbers in a substance in the smallest possible whole-number ratios.

Molecular Formula

A chemical formula that indicates the actual number of atoms of each element in one molecule of a substance.

Monatomic Ion

An ion consisting of exactly one atom.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Polyatomic Ion

An electrically charged group of two or more atoms.

Binary Acid

Certain molecular compounds in which hydrogen is combined with a second nonmetallic element.

Stoichiometry

The relationships among the quantities of reactants and products involved in chemical reactions.

Chemical Reaction

Processes in which a substance is transformed into a chemically different substance; also called chemical changes.

Chemical Equation

A representation of a chemical reaction using the chemical formulas of the reactants and products; a balanced chemical equation contains equal numbers of atoms of each element on both sides of the equation.

Reactant

A starting substance in a chemical reaction; it appears to the left of the arrow in a chemical equation.

Product

A substance produced in a chemical reaction; it appears to the right of the arrow in a chemical equation.

Composition (Synthesis Reaction)

A reaction in which two or more substances combine to form a new compound.

Decomposition

A reaction in which a single compound breaks down to form two or more simpler substances.

Combustion

A chemical reaction that proceeds with evolution of heat and usually also a flame; involves reaction with oxygen, as in the burning of a match.

Avogadro’s Number

The number of particles in a mole. 6.02×10²³

Mole

A base unit that is used to measure the amount of a substance, it is Avogadro’s Number.

Molar Mass

The mass of one mole of a substance in grams; it is numerically equal to the formula weight in atomic mass units.

Percent Composition

The percentage by mass of each element in a compound.

Hydrate

Any compound that contains H₂O molecules.

Limiting Reactant

The reactant that is completely consumed in a reaction; the amount of product that can form is limited by the complete consumption of it.

Excess Reactant

The reactant that is not completely used up in a chemical reaction.

Theoretical Yield

The quantity of a product that is calculated to form when all of the limithing reagent reacts.

Actual Yield

The actual measured amount of product obtained from a reaction.

Percent Yield

The ratio of the actual (experimental) yield of a product to its theoretical (calculated) yield, multiplied by 100.

Hygroscopic

Hydrates and other compounds that remove moisture from the air.

Deliquescent

The process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution.

Efflorescent

The spontaneous loss of water by a hydrated salt.

Electromagnetic Radiation

A form of energy that has wave characteristics and that propagates through a vacuum at the characteristic speed of 3.00 × 10^8 m/s.

Wavelength

The distance between identical points (such as two adjacent peaks or two adjacent troughs) on successive waves.

Frequency

The number of times per second that one complete wavelength passes a given point.

Electromagnetic Spectrum

The range of wavelengths or frequencies over which electromagnetic radiation extends.

Visible Spectrum

The portion of the electromagnetic spectrum that humans can see.

Quantum

The smallest increment of radiant energy that may be absorbed or emitted; the magnitude of radiant energy is hv.

Photon

The smallest increment (a quantum) of radiant energy; a photon of light with frequency (v) has an energy equal to (hv). They are quantized packets of energy.

Speed of Light

3.00 × 10^8 m/s

Emission Spectrum

A spectrum of the electromagnetic radiation emitted by a source.

Uncertainty Principle

A principle stating there is an inherent uncertainty in the precision with which we can simultaneously specify the position and momentum of a particle. This uncertainty is significant only for particles of extremely small mass, such as electrons.

Pauli Exclusion Principle

A rule stating that no two electrons in an atom may have the same four quantum numbers (n, l, m_l, and m_s). As a reflection of this principle, there can be no more than two electrons in any one atomic orbital.

Orbital

An allowed energy state of an electron in the quantum-mechanical model of the atom; the term is also used to describe the spatial distribution of the electron. Defined by the values of three quantum numbers: n, l, and m_l.

Electron Configuration

The arrangement of electrons in the orbitals of an atom or molecule.

Paramagnetic

A property that a substance possesses if it contains one or more unpaired electrons. This substance is drawn into a magnetic field.

Diamagnetic

A type of magnetism that causes a substance with no unpaired electrons to be weakly repelled from a magnetic field.

Ground State

The lowest-energy, or most stable, state.

Excited State

A higher energy state than the ground state.

Valence Electrons

The outermost electrons of an atom; used in bonding.

Core Electrons

The electrons in the inner shells of an atom; these electrons are not involved in forming bonds.

Effective Nuclear Charge

The net positive charge experienced by an electron in a many-electron atom; this charge is not the full nuclear charge because there is some shielding of the nucleus by the other electrons in the atom.

Shielding Effect

The reduction of the attractive force between a nucleus and its outer electrons due to the blocking effect of inner electrons.

Atomic Radius

One-half the distance between the nuclei of two atoms of the same element when the atoms are joined.

First Ionization Energy

The energy required to remove the first electron from ground state of a gaseous atom.

Second Ionization Energy

The energy required to remove the second electron from ground state of a gaseous atom.

Electron Affinity

The energy change that occurs when an electron is added to a gaseous atom or ion.

Metal

Elements that are usually solids at room temp, exhibit high electrical and heat conductivity and appear lustrous. Most of the elements in the periodic table are this.

Nonmetal

Elements in the upper right corner of periodic table; are poor conductors and not malleable.

Alkali Metals

Group 1, very active elements which form basic solutions and hydrogen gas when added to water.

Alkaline Earth Metals

Group 2, generally active elements which form basic solutions.

Allotrope

Different forms of the same element having different molecular structures, in the same physical state.

Halogens

Group 17, active elements which readily form ionic salts with metals, variable oxidation states.

Noble Gases

Group 18, generally unreactive nonmetals with completely filled s and p orbitals.

Joule

The SI unit of energy, 1 kg-m²/s².

1st Law of Thermodynamics

Energy cannot be created or destroyed.

Exothermic

A process in which a system releases heat to its surroundings.

Endothermic

A process in which a system absorbs heat from its surroundings.