Elements: any of the substances that cannot be chemically interconverted or broken down into simpler substances and are primary constituent of matter. (Oxford)

A substance that contains atoms of only one variety. The basic materials that make up all matter. Some matter may be made up of only one element, but most matter is made up of more than one element. (Shultz, 7-8) Just four elements - oxygen, carbon, hydrogen, and nitrogen, account for the vast majority of atoms in living organisms. Much of the hydrogen and oxygen occur in the form of water, which accounts for approximately 60% of the mass of most animals and 95% or more in some plants. (Booker, 27)

Atom(s): the smallest component of an element that has the chemical properties of the element. All "matter" is composed of atoms. (Brooker, 4) Cannot be further broken down into other substances by ordinary chemical or physical means. (Brooker, 21) Adjective - 'atomic.'

Atomic Number: number of protons in an element. (Norman, 6/11/09)

Electron: subatomic particle found within atoms. (Brooker, 21) An elementary particle which carries a negative electric charge. (Chapple, 77) Positively charged electrons are called ‘positrons.’ The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. (NCIt)

Mass: a coherent body of matter of unspecified shape. A solid, physical object. (Oxford) The amount of matter in an object. (NCIt) Editor’s note - ‘atomic mass’ is the weight of protons and neutrons. Each weighs 1 atomic mass unit.

Matter: anything that has mass and occupies space. Examples are solids, liquids, gas. (Norman, 6/11/09)

Neutron: subatomic particle found in the cell "nucleus” that has no electrical charge. (Brooker, 21) An elementary particle with a mass almost the same as that of a hydrogen atom. (Chapple, 163) An elementary particle with zero charge and a mass about equal to that of a proton. (NCIt)

Orbital: physical location of an electron 90% of the time. (Norman, 6/11/09)

Proton: subatomic particle with one unit of positive charge. (Brooker, 21) An elementary particle whose mass is almost equal to that of a hydrogen atom. A hydrogen atom has just a proton for its nucleus. (Chapple, 191)

Shells: the main energy levels in atoms. (Hunt, 314) 

Electron Valence Shell: the highest energy level of an electron. Contains electrons involved in chemical bonds. The goal of atoms is to fill their valence shell with as many electrons as that shell holds in order to generate the most stable molecule possible. Depending on the element, electron valence shells have a capacity of 2, 8, 18 ... electrons. Electrons will pair up when half of the shell capacity is full. (Norman, 6/11/09) 

Subatomic Particles: particles inside the atom. These include protons, neutrons, and electrons. (Norman, 6/11/09)

Van der Waals Forces: the weak attraction of atoms within molecules at an optimal distance apart. Can contribute to protein folding and stability. (Brooker, 54) Of importance of forming and maintaining the three-dimensional structure of proteins and in interactions between proteins. (Lawrence)

Carbon: non-metal element found in all forms of life. (Brooker, 41) Major building block of of all living matter. (Booker, 27) One of the properties of the carbon atom that makes life possible is its ability to form four "covalent bonds" with other atoms including carbon. Carbon atoms can bond to several biologically important "functional groups." Carbon-containing molecules may exist in multiple forms (called “isomers”). (Brooker, 42-44) A non-metallic element with symbol ‘C,’ atomic number 6, and atomic weight 12. (NCIt)

Alpha-Carbon: a carbon atom which is part of the structure of an “amino acid.” Linked to an “amino” group. Linked to a hydrogen atom. Linked to a amino acid side chain. (Brooker, 50)

Carbon Dioxide: a colorless, odorless, un-reactive gas. A gas from the air that is critically important to the growth and mass of plants. (Brooker, 150) It is a waste product made by the body. Carbon dioxide travels in the blood from the body's tissues to the “lungs.” Breathing out clears carbon dioxide from the lungs. (NCIt)

Carbon Footprint: the amount of carbon dioxide emitted due to the activities, especially the consumption of fossil fuels, of a particular person, group, etc. (Oxford) A measure of the total greenhouse gas emissions produced by an individual, organization, event, or product. It is measured in units of equivalent kilograms of carbon dioxide generated in a given time frame. (MeSH)

Carbon Monoxide: a colorless gas with no smell, formed by the incomplete combustion of fuels containing carbon. The gas is highly poisonous because it is held much more strongly by blood “hemoglobin” than “oxygen.” Death results when most of the hemoglobin is blocked (inhibited) by carbon monoxide. (Hunt, 73) A poisonous gas that has no color or odor. It is given off by burning fuel (as in exhaust from cars or household heaters) and tobacco products. Carbon monoxide prevents red blood cells from carrying enough oxygen for cells and tissues to live. (NCIt)

Hydrocarbons: compounds which consist of just carbon and hydrogen. (Hunt, 184) 

Chlorine: a powerful oxidizing agent which reacts directly with most elements. Forms "chlorides" with most nonmetals but it does not react directly with carbon, oxygen or nitrogen. Dissolves in water. (Hunt, 86) An extremely pungent gaseous element with antiseptic and bleaching properties. It is widely used to sterilize drinking water and purify swimming pools. In high concentrations it is toxic. (OxfordMed) A chemical used in manufacturing, as a bleach, and to kill bacteria and other organisms in water. An element with atomic symbol ‘Cl,’ atomic number 17, and atomic weight 35.05. (NCIt)

Chloride: a compound of chlorine. (Oxford)

Hydrogen: the commonest element in the universe. Hydrogen atoms are the smallest of all atoms consisting, normally, of one proton and one electron. (Hunt, 184) The first chemical element in the periodic table. It exists, under normal conditions, as a colorless, odorless, tasteless, diatomic gas. Hydrogen “ions” are protons. Besides the common ‘H1 isotope,’ hydrogen exists as the stable isotope ‘deuterium’ and the unstable, radioactive isotope ‘tritium.’ It has the atomic symbol ‘H,’ atomic number 1, and atomic weight 1.00784. (MeSH)

Isotope: a form of a chemical element in which the atoms have the same number of protons but with a different number of neutrons. For example, carbon 12, carbon 13, and carbon 14 are isotopes of carbon. They all have six protons in the nucleus, but each has a different number of neutrons. Isotopes may be used in certain medical tests and procedures. (NCI1)

Radioisotope: an unstable form of a chemical element that releases radiation as it breaks down and becomes more stable. Radioisotopes may occur in nature or be made in a laboratory. In medicine, they are used in imaging tests and in treatment. (NCI1) Also referred to as ‘radionuclide.’

Metals: elements on the left-hand side of the “periodic table” with one, two or three electrons in the outer “shell” which take part in “bonding” and “chemical reactions.” (Hunt, 231)

Gold: a yellow metallic element with the atomic symbol 'Au,' atomic number 79, and atomic weight 197. It is used in jewelry, gold-plating of other metals, as currency, and in dental restoration. Many of its clinical applications are in the form of its salts. (MeSH)

Silver: a precious metal which is characterized by its lustrous color and great malleability and ductility. (Oxford) A soft metal that is used medically in surgical instruments, dental prostheses, and alloys. An element with the atomic symbol ‘Ag,’ atomic number 47, and atomic weight 107.87. (MeSH)

Minerals: inorganic ions required by a living organism. (Booker, G-23) Important for (the) body to stay healthy. (The) body uses minerals for many different jobs, including building bones, making hormones and regulating heartbeat. (MedlinePlus)

Calcium: a mineral needed for healthy teeth, bones, and other body tissues. It is the most common mineral in the body. A deposit of calcium in body tissues, such as breast tissue, may be a sign of disease. (NCIt) A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of “metals” with the atomic symbol ‘Ca,’ atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with “phosphorus” to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of “nerves” and “muscles” and plays a role in blood (clotting) and in many enzyme processes. (MeSH)

Macrominerals: minerals (the) body needs in larger amounts. They include calcium, phosphorus, magnesium, sodium, potassium, chloride and sulfur. (MedlinePlus)

Phosphorus: a nonmetallic element that is found in the blood, muscles, nerves, bones, and teeth and is a component of adenosine triphosphate (the primary energy source for the body's cells). (NCIt) Phosphorus compounds are major constituents in the tissues of both plants and animals. In humans, phosphorus is mostly concentrated in bone. Certain phosphorus containing compounds, for example ATP, play an important part in energy conversions and storage in the body. In a pure state, phosphorus is toxic. (OxfordMed) A highly reactive element and important nonmetal. (Includes) 'white phosphorus' which has to be stored under water otherwise it catches fire in air, and 'red phosphorus' which is more stable and does not catch fire in air. (Hunt, 276) An essential element that takes part in a broad variety of biochemical reactions. A non-metal element that has the atomic symbol ‘P’, atomic number 15, and atomic weight 31. (MeSH)

Potassium: a soft light pinkish-white, highly reactive chemical element which is present in numerous minerals, and whose salts are essential to biological processes. (Oxford) A metallic element that is important in body functions such as regulation of “blood pressure” and of water content in cells, transmission of nerve “impulses,” "digestion," muscle contraction, and "heartbeat." (NCIt) Stored in oil, floats on water, and is an essential nutrient for plants. (Hunt, 287) (A nutrient found in) meats, fruits, vegetables, dairy foods, and grains. (Booker, 866) An element that is in the "alkali" group of metals. It is the chief “cation” in the "intracellular" fluid of muscle and other cells. A potassium ion is a strong “electrolyte” and plays a significant role in the regulation of fluid volume and maintenance of the 'water-electrolyte balance.' It has an atomic symbol ‘K’, atomic number 19, and atomic weight 39.10. (MeSH)

Sodium: a soft wax-like silvery-white highly reactive chemical element present in seawater as common salt and in numerous minerals, and whose salts are essential to biological processes. (Oxford) Soft, shiny metal which rapidly tarnishes in moist air. (Hunt, 319) A member of the alkali group of metals. Minerals like sodium and potassium are key regulators of water movement and electrical currents that occur across the surfaces of many cells. (Booker, 27) A mineral needed by the body to keep body fluids in balance. Sodium is found in table salt and in many processed foods. Too much sodium can cause the body to retain water. (NCIt) It has the atomic symbol ‘Na’, atomic number 11, and atomic weight 23. (MeSH)

Trace Minerals: the body needs just small amounts of trace minerals. These include iron, manganese, copper, iodine, zinc, cobalt, fluoride and selenium. (MedlinePlus) Essential for normal growth and function. (Booker, 27)

Nitrogen: a gaseous element and a major constituent of air. Obtained by animals in the form of protein-containing foods (symbol N). (OxfordMed) A vital element in all proteins. (Booker, 27) Forms part of the molecules which make up "amino acids," proteins, and nucleic acids. (Indge, 185) Nitrogen exists as a diatomic gas and makes up about 78% of the earth's atmosphere by volume. Found in all living cells. An element with the atomic symbol ’N,’ atomic number 7, and atomic weight 14.00643. (MeSH)

Ammonia: a colorless inorganic compound of nitrogen and hydrogen with the formula NH3, usually in gaseous form with a characteristic pungent odor. Ammonia is irritating to the skin, eyes, nose, throat, and lungs. It is essential for many biological processes and has various industrial applications. (NCIt)

Oxygen: an odorless colorless gas that makes up one-fifth of the atmosphere. Essential to most forms of life in that it combines chemically with “glucose” to provide energy for “metabolic” processes. It is absorbed into the “blood” from air breathed into the "lungs." (OxfordMed) It is needed for animal and plant life. Oxygen that is breathed in enters the blood from the lungs and travels to the tissues. (NCIt) Green plants produce oxygen by photosynthesis in sunlight. Combines with most other elements to form 'oxides.' Particularly important is water, the oxide of hydrogen. (Hunt, 262) It is the most abundant element on earth and essential for “respiration.” An element with atomic symbol ‘O’, atomic number 8, and atomic weight 15.99903. (MeSH) Adjective - 'oxygenated.'

Oxides: compounds of elements with oxygen. The compounds of metals with oxygen are ‘basic oxides.’ The compounds with nonmetals with oxygen are either ‘acidic oxides’ or ‘neutral oxides.’ (Hunt, 260)

Ozone: gas formed from oxygen under the action of short-wavelength ultraviolet radiation in the ‘stratosphere’ where it forms the ‘ozone layer.’ This absorbs considerable “ultraviolet radiation” and shields the Earth’s surface from its harmful effects. (Lawrence) The unstable form of oxygen, O3. It is a powerful oxidant that is produced for various chemical and industrial uses. Its production is also catalyzed in the atmosphere by (ultraviolet radiation) of oxygen or other ozone “precursors” such as volatile organic compounds and nitrogen oxides. About 90% of the ozone in the atmosphere exists in the stratosphere. (MeSH)

Periodic Table: a table of the elements arranged in order of “atomic number.” (Hunt, 268)