| A | B |
|---|
| element | pure substance that cannot be broken down into other substances by chemical or physical means |
| compound | substance containing two or more elements chemically combined in a fixed ratio |
| trace element | element critical to health that makes up less than 0.01 percent of body mass |
| matter | anything that occupies space and has mass |
| atom | smallest particle of an element |
| atomic number | number of protons in an atom's nucleus |
| electron | subatomic particle with a single unit of negative electric charge |
| isotope | one of several forms of an element, each containing the same number of protons in their atoms but a different number of neutrons |
| neutron | neutral particle in nucleus of an atom |
| nucleus | in an atom, the central core that contains protons and neutrons |
| proton | subatomic particle with a single unit of positive electric charge |
| radioactive isotope | isotope in which the nucleus decays (breaks down) over time, giving off radiation in the form of matter and energy |
| chemical reaction | breaking of old and formation of new chemical bonds that result in new substances |
| covalent bond | chemical bond that forms when two atoms share electrons (Concept 4.3) |
| ion | atom that has become electrically charged as a result of gaining or losing an electron |
| ionic bond | chemical bond that occurs when an atom transfers an electron to another atom |
| molecule | two or more atoms held together by covalent bonds |
| product | material created as a result of a chemical reaction |
| reactant | starting material for a chemical reaction |
| acid | compound that donates H+ ions to an aqueous solution and measures less than 7 on the pH scale |
| adhesion | attraction between unlike molecules |
| aqueous solution | solution in which water is the solvent |
| base | compound that removes H+ ions from an aqueous solution and that measures more than 7 on the pH scale |
| buffer | substance that maintains a fairly constant pH in a solution |
| cohesion | tendency of molecules of the same kind to stick to one another |
| hydrogen bond | bond created by the weak attraction of a slightly positive hydrogen atom to a slightly negative portion of another molecule |
| pH scale | a range of numbers used to describe how acidic or basic a solution is; ranges from 0 (most acidic) to 14 (most basic) |
| polar molecule | molecule in which opposite ends have opposite electric charges |
| solute | substance in a solution that is dissolved and is present in a lesser amount |
| solution | uniform mixture of two or more substances |
| solvent | substance in a solution that dissolves the other substance and is present in the greater amount |
| temperature | measure of the average energy of random motion of particles in a substance |
| theory | well-tested explanation that makes sense of a great variety of scientific observations |
| thermal energy | total amount of energy associated with the random movement of atoms and molecules in a sample of matter |
