Visionlearning Glossary

The theoretical lowest temperature possible at which all molecular motion ceases. Absolute zero, 0 K or -273.15°C, has never been reached.

Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different scientists (listed in parentheses). 1) (Arrhenius) a compound that releases hydrogen ions (H+) in solution; 2) (Brønsted-Lowry) a compound capable of donating hydrogen ions, 3) (Lewis) a compound that can accept a pair of electrons from a base.

Rain with a pH less than 5.

The energy required to initiate a chemical reaction or process, abbreviated E_a. For example, a cigarette lighter requires activation energy (provided in the form of a spark) to initiate the reaction of fuel with oxygen.

To adhere in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the surfaces of solid bodies or liquids with which a substance is in contact.

The semi-molten layer of the earth which starts at ~70-200 km depth and ends at 660 km depth. The aesthenosphere is part of the mantle, and is composed primarily of the rock peridotite. The aesthenosphere can flow very slowly, allowing rigid pieces of the lithosphere to move around on top of it.

An organic compound containing a hydroxyl group. Common examples include methanol (CH₃OH) and ethanol (CH₃CH₂OH).

A group of hydrocarbons with the general formula C_nH_(2n+2). Alkanes contain no carbon-carbon multiple bonds; common examples include methane and propane.

A group of hydrocarbons with the general formula C_nH_(2n). Alkenes contain at least one carbon-carbon double bond; common examples include ethylene.

A group of hydrocarbons with the general formula C_nH_(2n-2). Alkynes contain at least one carbon-carbon triple bond; common examples include ethyne also known as acetylene.

A variation of a genetic element, usually resulting in a distinct trait.

A type of particle that is ejected from radioactive nuclei. Alpha particles consist of two protons and two neutrons and thus are equivalent to helium nuclei.

Pertaining to an alveolus.

The plural of alveolus.

A small sac-like structure in the body, especially common in the lung. A lung alveolus has extremely thin walls that aid in the exchange of gases including O₂ and CO₂.

Biochemical molecules that contain at least one amine group (-NH₂) and at least one carboxylic acid group (-COOH) and conform to the general formula NH₂-R-COOH, where R is an organic molecule. Amino acids are essential basic building blocks of proteins.

Having the ability to live both on land and in water.

A convergent plate boundary, where oceanic crust is being subducted beneath continental crust. Named after the Andes Mountains in South America, which are the classic example of a continent-ocean convergence.

An extrusive igneous rock of intermediate composition, often gray in color. The main minerals present in andesite are plagioclase and hornblende. The word “andesite” comes from the Andes Mountains in South America, where this rock type is common. Around the world, andesitic magma erupts out of volcanoes along convergent boundaries, and its intrusive equivalent is diorite.

A unit of length equivalent to 10^-10 meters. 1Å = 0.0000000001 m.

An ion that migrates to the anode in an electrical cell; a negatively charged ion.

A positively charged terminal in an electrical cell.

Male part of a flowering plant that holds pollen.

A porous and permeable body of rock or sediment through which groundwater flows.

The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in combinations with other atoms forming molecules.

The average mass of an atom of an element, usually expressed in atomic mass units. The term is often used interchangeably with atomic weight.

One atomic mass unit (amu or u) is defined as 1/12 the mass of the standard carbon-12 isotope, or 1.66 × 10^-27 kg.

The number of protons in an atomic nucleus.

Compare with Bohr radius and hartree.A system of non-SI units used in quantum chemistry to simplify calculations and mathematical expressions. The definitions of atomic units include physical constants (like the speed of light, the rest mass of the electron, and other quantities that never change), so that all constants drop out of expressions when atomic units are used.

As listed on the periodic table, the atomic weight is a weighted average of the masses of stable isotopes of an element that occur in nature. Given in grams, the atomic weight is the weight of one mole of atoms of an element. Atomic weight is often used interchangeably with atomic mass.

The behavior of waves as they radiate out from a source. As distance from the source increases, intensity of the waves decreases. Attenuation occurs because the same amount of energy is being spread out over a larger area.