| A | B |
|---|
| acid | A substance that increases the hydrogen ion concentration in a solution. |
| acid precipitation | Rain, snow, or fog with a pH below 5.6. |
| adhesion | The attraction between different kinds of molecules. |
| aqueous solution | A solution in which water is the solvent. |
| atom | The small unit of matter that retains the properties of an element. |
| atomic mass | The approximate total mass of an atom; also called atomic weight. Given as a whole number, the atomic mass approximately equals the mass number. |
| atomic number | The number of protons in each atom of a particular element. |
| base | A substance that decreases the hydrogen ion (H) concentration in a solution. |
| buffer | A chemical substance that resists changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions. |
| chemical bond | An attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells. |
| chemical reaction | The making and breaking of chemical bonds, leading to changes in the composition of matter. |
| cohesion | The binding together of like molecules, often by hydrogen bonds. |
| compound | A substance containing two or more elements in a fixed ratio. For example, table salt (NaCl) consists of one atom of the element sodium (Na) for every atom of chlorine (Cl). |
| covalent bond | An attraction between atoms that share one or more pairs of outer-shell electrons; symbolized by a single line between the atoms. |
| double bond | A type of covalent bond in which two atoms share two pairs of electrons; symbolized by a pair of lines between the bonded atoms. |
| electron | A subatomic particle with a single negative electrical charge. One or more electrons move around the nucleus of an atom. |
| electron shell | An energy level representing the distance of an electron from the nucleus of an atom. |
| electronegativity | The attraction of a given atom for the electrons of a covalent bond. |
| element | A substance that cannot be broken down to other substances by chemical means. |
| heat | Thermal energy; the amount of energy associated with the movement of the atoms and molecules in a body of matter. Heat is energy in its most random form. |
| hydrogen bond | A type of weak chemical bond formed when the partially positive hydrogen atom participating in a polar covalent bond in one molecule is attracted to the partially negative atom participating in a polar covalent bond in another molecule (or in another part of the same macromolecule). |
| ion | An atom that has gained or lost one or more electrons, thus acquiring a charge. |
| ionic bond | A chemical bond resulting from the attraction between oppositely charged ions. |
| isotope | A variant form of an atom. Isotopes of an element have the same number of protons but different numbers of neutrons. |
| mass number | The sum of the number of protons and neutrons in an atom's nucleus. |
| matter | Anything that occupies space and has mass. |
| molecule | A group of two or more atoms held together by covalent bonds. |
| neutron | An electrically neutral particle (a particle having no electrical charge), found in the nucleus of an atom. |
| nonpolar covalent bond | A covalent bond in which electrons are shared equally between two atoms of similar electronegativity. |
| nucleus | (plural, nuclei) (1) An atom's central core, containing protons and neutrons. (2) The genetic control center of a eukaryotic cell. |
| pH scale | A measure of the relative acidity of a solution, ranging in value from 0 (most acidic) to 14 (most basic). The letters pH stand for potential hydrogen and refer to the concentration of hydrogen ions (H). |
| polar covalent bond | A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive. |
| polar molecule | A molecule containing polar covalent bonds. |
| product | An ending material in a chemical reaction. |
| proton | A subatomic particle with a single positive electrical charge, found in the nucleus of an atom. |
| radioactive isotope | An isotope whose nucleus decays spontaneously, giving off particles and energy. |
| reactant | A starting material in a chemical reaction. |
| salt | A compound resulting from the formation of ionic bonds; also called an ionic compound. |
| solute | A substance that is dissolved in a solution. |
| solution | A liquid consisting of a homogeneous mixture of two or more substances, consisting of a dissolving agent, called the solvent, and a substance that is dissolved, called the solute. |
| solvent | The dissolving agent of a solution. Water is the most versatile solvent known. |
| surface tension | A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules. |
| temperature | A measure of the intensity of heat in degrees, reflecting the average kinetic energy or speed of molecules. |
| trace element | An element that is essential for life but required in extremely minute amounts. |
