| Term | Definition |
| matter | Anything that occupies space and has mass. |
| Mass | A measurement of the amount of matter an object contains. |
| Atom | The smallest particle that can contain the chemical properties of an element. |
| Element | A substance composed of atoms that cannot be broken down into smaller, simpler components. |
| Periodic table | A chart of all chemical elements currently known, organized by their properties. |
| Molecule | A particle that contains more than one atom. |
| Compound | A molecule containing more than one element. |
| Atomic number | The number of protons in the nucleus of a particular element. |
| Mass number | A measurement of the total number of protons and neutrons in an element. |
| Isotopes | Atoms of the same element with different numbers of neutrons. |
| Radioactive decay | The spontaneous release of material from the nucleus of radioactive isotopes. |
| Half-life | The time it takes for one-half of an original radioactive parent atom to decay. |
| Covalent bond | The bond formed when elements share electrons. |
| Ionic bond | A chemical bond between two ions of opposite charges. |
| Hydrogen bond | A weak chemical bond that forms when hydrogen atoms that are covalently bonded to one atom are attracted to another atom on another molecule. |
| Polar molecule | A molecule in which one side is more positive and the other side is more negative. |
| Surface tension | A property of water that results from the cohesion of water molecules at the surface of a body of water and that creates a sort of skin on the water’s surface. |
| Capillary action | A property of water that occurs when adhesion of water molecules to a surface is stronger than cohesion between the molecules. |
| Acid | A substance that contributes hydrogen ions to a solution. |
| Base | A substance that contributes hydroxide ions to a solution. |
| pH | The number that indicates the relative strength of acids and bases in a substance. |
| Chemical reaction | A reaction that occurs when atoms separate from molecules or recombine with other molecules. |
| Law of conservation of matter | A law of nature stating that matter cannot be created or destroyed; it can only change form. |
| Inorganic compound | A compound that does not contain the element carbon or contains carbon bound to elements other than hydrogen. |
| Organic compound | A compound that contains carbon-carbon and carbon-hydrogen bonds. |
| Carbohydrate | A compound composed of carbon, hydrogen, and oxygen atoms. |
| Protein | A critical component of living organisms made up of a long chain of nitrogen-containing organic molecules known as amino acids. |
| Nucleic acid | Organic compounds found in all living cells. |
| DNA (deoxyribonucleic acid) | A nucleic acid, the genetic material that contains the code for reproducing the components of the next generation, and which organisms pass on to their offspring. |
| RNA (ribonucleic acid) | A nucleic acid that translates the code stored in DNA, which makes possible the synthesis of proteins. |
| Lipid | A smaller organic biological molecule that does not mix with water. |
| Cell | A highly organized living entity that consists of the four types of macromolecules and other substances in a watery solution, surrounded by a membrane. |
| Energy | The ability to do work or transfer heat. |
| Joule | The amount of energy used when a 1-watt electrical device is turned on for 1 second. |
| Power | The rate at which work is done. |
| Electromagnetic radiation | A form of energy emitted by the Sun that includes, but is not limited to, visible light, ultraviolet light, and infrared energy. |
| Photon | A massless packet of energy that carries electromagnetic radiation at the speed of light. |
| Potential energy | Stored energy that has not been released. |
| Chemical energy | Potential energy stored in chemical bonds. |
| Kinetic energy | The energy of motion. |
| Temperature | The measure of the average kinetic energy of a substance. |
| First law of thermodynamics | A physical law which states that energy can neither be created nor destroyed but can change from one form to another. |
| Second law of thermodynamics | The physical law stating that when energy is transformed, the quantity of energy remains the same, but its ability to do work diminishes. |
| Energy efficiency | The ratio of the amount of energy expended in the form you want to the total amount of energy that is introduced into the system. |
| Energy quality | The ease with which an energy source can be used for work. |
| Entropy | Randomness in a system. |
| Open system | A system in which exchanges of matter or energy occur across system boundaries. |
| Closed system | A system in which matter and energy exchanges do not occur across boundaries. |
| Input | An addition to a system. |
| Output | A loss from a system. |
| Systems analysis | An analysis to determine inputs, outputs, and changes in a system under various conditions. |
| Steady state | A state in which inputs equal outputs, so that the system is not changing over time. |
| Negative feedback loop | A feedback loop in which a system responds to a change by returning to its original state, or by decreasing the rate at which the change is occurring. |
| Positive feedback loop | A feedback loop in which change in a system is amplified. |
