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| Anything that occupies space and has mass.Matter, in forms as diverse as rock, water, gases, and living organisms, is composed of chemical elements |
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| A substance that cannot be broken down to other substances by chemical means. |
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| An element that is essential for life but required in extremely minute amounts. |
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| Which four chemical elements are most abundant in living matter? |
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| Oxygen, carbon, hydrogen, and nitrogen |
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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 small 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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| (plural, nuclei) (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. All atoms of a particular element have the same unique number of protons. |
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| The sum of the 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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| 1) An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons. |
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| Why are radioactive isotopes useful as tracers in research on the chemistry of life? |
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| Organisms incorporate radioactive isotopes of an element into their molecules just as they do nonradioactive isotopes, and researchers can use special scanning devices to detect the presence of the radioactive isotopes. |
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| Only electrons are directly involved in the chemical activity of an atom. The farther an electron is from the nucleus, the greater its energy |
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| By transferring or sharing electrons, atoms complete their outer shells. These interactions between atoms create chemical bonds. |
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| An atom that has gained or lost one or more electrons, thus acquiring a charge. |
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| A chemical bond resulting from the attraction between oppositely charged ions. |
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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 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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| Two or more atoms held together by covalent bonds. |
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| The attraction of a given atom for the electrons of a covalent bond. The more electronegative an atom, the more strongly it pulls shared electrons toward its nucleus. |
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| A covalent bond in which electrons are shared equally between two atoms of similar electronegativity. |
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| 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. |
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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 binding together of like molecules, often by hydrogen bonds. |
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| The attraction between different kinds of molecules. |
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| 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. |
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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 in degrees, 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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| 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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| 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 concentration 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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| An acid is any substance that increases the H+ concentration of a solution. A base is any substance that reduces the H+ concentration of a solution. Move your cursor up or down in the pH scale to add acid or base to our solution. |
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| Rain, snow, or fog with a pH below 5.6. |
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| The making and breaking of chemical bonds, leading to changes in the composition of matter. |
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| A starting material in a chemical reaction. |
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| An ending material in a chemical reaction. |
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