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anything that occupies space and has mass |
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a substance that cannot be broken down to other substances by chemical means. Scientists recognize 92 chemical elements occurring in nature. |
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| an element that is essential for the survival of an organism but only in minute quantities. |
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| 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). |
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| the smallest unit of matter that retains the properties of an element. |
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| a subatomic particle with a single positive electrical charge, found in the nucleus of an atom. |
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| a subatomic particle with a single negative electrical charge. One or more electrons move around the nucleus of an atom. |
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| an electrically neutral particle (a particle having no electrical charge), found in the nucleus of an atom. |
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(1) an atom's central core, containing protons and neutrons. (2) the genetic control center of a eukaryotic cell. |
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| the number of protons in each atom of a particular element. |
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the sum of number of protons and neutrons in an atom's nucleus |
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| the approximate total mass of an atom; also called atomic weight. Given as a whole number, the atomic mass approximately equals the mass number. |
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| a variant form of an atom. Isotopes of an element have the same number of protons but different numbers of neutrons. |
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| an isotope whose nucleus decays spontaneously, giving off particles and energy. |
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| an energy level representing the distance of an electron from the nucleus of an atom. |
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| 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. |
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| an atom or molecule that has gained or lost one or more electrons, thus acquiring an electrical charge. |
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| an attraction between two ions with opposite electrical charges. The electrical attraction of the opposite charges holds the ions together. |
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| a compound resulting from the formation of ionic bonds; also called an ionic compound. |
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| an attraction between atoms that share one or more pairs of outer-shell electrons; symbolized by a single line between the atoms. |
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| a group of two or more atoms held together by covalent bonds. |
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| a type of covalent bond in which two atoms share two pairs of electrons; symbolized by a pair of lines between the bonded atoms. |
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| the tendency for an atom to pull electrons toward itself. |
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| an attraction between atoms that share one or more pairs of electrons equally because the atoms have similar electronegativity. |
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| an attraction between atoms that share electrons unequally because the atoms differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it partially negative and the other atom partially positive. |
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| a molecule containing polar covalent bonds. |
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| 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). |
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| the attraction between molecules of the same kind. |
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| a measure of how difficult it is to stretch or break the surface of a liquid. |
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| 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. |
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| a measure of the intensity of heat, reflecting the average kinetic energy or speed of molecules. |
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| 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. |
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| the dissolving agent in a solution. Water is the most versatile known solvent. |
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| a substance that is dissolved in a solution. |
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| a solution in which water is the solvent. |
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| a substance that increases the hydrogen ion concentration in a solution. |
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| a substance that decreases the hydrogen ion (H+) concentration in a solution. |
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| 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 ocncentration of hydrogen ions (H+). |
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| a chemical substance that resists changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions. |
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| rain, snow, sleet, hail, drizzle, and so on, with a pH below 5.6. Acid precipitation can damage or destroy organisms by acidifying lakes, streams, and possibly land habitats. |
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| a process leading to changes in the composition of matter; involves the making and/or breaking of chemical bonds. |
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| a starting material in a chemical reaction. |
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