alpha particle Positively charged matter, consisting of two neutrons and two protons, that is emitted as a form of radioactivity from the nuclei of some radioisotopes. See also beta particle, gamma rays.

atom Minute unit made of subatomic particles that is the basic building block of all chemical elements and thus all matter; the smallest unit of an element that can exist and still have the unique characteristics of that element. Compare ion, molecule.

atomic number Number of protons in the nucleus of an atom. Compare mass number.

beta particle Swiftly moving electron emitted by the nucleus of a radioactive isotope. See also alpha particle, gamma rays.

Biodegradable pollutant Material that can be broken down into simpler substances (elements and compounds) by bacteria or other decomposers. Paper and most organic wastes such as animal manure are biodegradable but can take decades to biodegrade in modern landfills. Compare degradable pollutant, nondegradable pollutant, slowly degradable pollutant.

calorie Unit of energy; amount of energy needed to raise the temperature of 1 gram of water 1 degree C (unit on Celsius temperature scale). See also kilocalorie.

CFCs See chlorofluorocarbons.

chain reaction Multiple nuclear fissions, taking place within a certain mass of a fissionable isotope, that release an enormous amount of energy in a short time. See nuclear.

chemical One of the millions of different elements and compounds found naturally and synthesized by humans. See compound, element.

chemical change Interaction between chemicals in which there is a change in the chemical composition of the elements or compounds involved. Compare nuclear change, physical change.

chemical formula Shorthand way to show the number of atoms (or ions) in the basic structural unit of a compound. Examples are H2O, NaCl, and C6H12O6.

chemical reaction See chemical change.

chlorinated hydrocarbon Organic compound made up of atoms of carbon, hydrogen, and chlorine. Examples are DDT and PCBs.

chlorofluorocarbons (CFCs) Organic compounds made up of atoms of carbon, chlorine, and fluorine. An example is Freon-12 (CCl2F2), used as a refrigerant in refrigerators and air conditioners and in making plastics such as Styrofoam. Gaseous CFCs can deplete the ozone layer when they slowly rise into the stratosphere and their chlorine atoms react with ozone molecules.

chromosome Grouping of various genes and associated proteins in plant and animal cells that carry certain types of genetic information. See genes.

closed system System in which energy but not matter is exchanged between the system and its environment. Compare open system.

compound Combination of atoms, or oppositely charged ions, of two or more different elements held together by attractive forces called chemical bonds. Compare element.

concentration Amount of a chemical in a particular volume or weight of air, water, soil, or other medium.

consensus science Scientific data, models, theories, and laws that are widely accepted by scientists considered experts in the area of study. These results of science are very reliable. Compare frontier science.

critical mass Amount of fissionable nuclei needed to sustain a nuclear fission chain reaction.

deductive reasoning Using logic to arrive at a specific conclusion based on a generalization or premise. It goes from the general to the specific. Compare inductive reasoning.

degradable pollutant Potentially polluting chemical that is broken down completely or reduced to acceptable levels by natural physical, chemical, and biological processes. Compare iodegradable pollutant, nondegradable pollutant, slowly degradable pollutant.

deuterium (D; hydrogen-2) Isotope of the element hydrogen, with a nucleus containing one proton and one neutron and a mass number of 2.

electromagnetic radiation Forms of kinetic energy traveling as electromagnetic waves. Examples are radio waves, TV waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays. Compare ionizing radiation, nonionizing radiation.

electron (e) Tiny particle moving around outside the nucleus of an atom. Each electron has one unit of negative charge and almost no mass. Compare neutron, proton.

element Chemical, such as hydrogen (H), iron (Fe), sodium (Na), carbon (C), nitrogen (N), or oxygen (O), whose distinctly different atoms serve as the basic building blocks of all matter. There are 92 naturally occurring elements. Another 23 have been made in laboratories. Two or more elements combine to form compounds that make up most of the world's matter. Compare compound.

energy Capacity to do work by performing mechanical, physical, chemical, or electrical tasks or to cause a heat transfer between two objects at different temperatures.

energy efficiency Percentage of the total energy input that does useful work and is not converted into low-quality, usually useless heat in an energy conversion system or process. See energy quality, net energy. Compare material efficiency.

energy productivity See energy efficiency.

energy quality Ability of a form of energy to do useful work. High-temperature heat and the chemical energy in fossil fuels and nuclear fuels are concentrated high quality energy. Low-quality energy such as low-temperature heat is dispersed or diluted and cannot do much useful work. See high-quality energy, low-quality energy.

experiment Procedure a scientist uses to study some phenomenon under known conditions. Scientists conduct some experiments in the laboratory and others in nature. The resulting scientific data or facts must be verified or confirmed by repeated observations and measurements, ideally by several different investigators.

feedback loop Circuit of sensing, evaluating, and reacting to changes in environmental as a result of information fed back into a system; it occurs when one change leads to some other change, which eventually reinforces or slows the original change. See negative feedback loop, positive feedback loop.

first law of energy See first law of thermodynamics.

first law of thermodynamics In any physical or chemical change, no detectable amount of energy is created or destroyed, but in these processes energy can be changed from one form to another; you cannot get more energy out of something than you put in; in terms of energy quantity, you cannot get something for nothing (there is no free lunch). This law does not apply to nuclear changes, in which energy can be produced from small amounts of matter. See also Second law of thermodynamics.

fissionable isotope Isotope that can split apart when hit by a neutron at the right speed and thus undergo nuclear fission. Examples are uranium-235 and plutonium-239. See nuclear fission.

flows See throughputs.

Freons See chlorofluorocarbons.

frontier science Preliminary scientific data, hypotheses, and models that have not been widely tested and accepted. Compare consensus science.

gamma rays Form of ionizing electromagnetic radiation with a high energy content emitted by some radioisotopes. They readily penetrate body tissues. See also alpha particle, beta particle.

genes Coded units of information about specific traits that are passed on from parents to offspring during reproduction. They consist of segments of DNA molecules found in chromosomes.

half-life Time needed for one-half of the nuclei in a radioisotope to emit its radiation. Each radioisotope has a characteristic half-life, which may range from a few millionths of a second to several billion years. See radioisotope.

heat Total kinetic energy of all the randomly moving atoms, ions, or molecules within a given substance, excluding the overall motion of the whole object. Heat always flows spontaneously from a hot sample of matter to a colder sample of matter. This is one way to state the second law of thermodynamics. Compare temperature.

high-quality energy Energy that is concentrated and has great ability to perform useful work. Examples are high-temperature heat and the energy in electricity, coal, oil, gasoline, sunlight, and nuclei of uranium-235. Compare low-quality energy.

high-quality matter Matter that is concentrated and contains a high concentration of a useful resource. Compare low-quality matter.

high-throughput economy Situation in most advanced industrialized countries, in which ever-increasing economic growth is sustained by maximizing the rate at which matter and energy resources are used, with little emphasis on pollution prevention, recycling, reuse, reduction of unnecessary waste, and other forms of resource conservation. Compare low-throughput economy, matter-recycling economy.

high-waste society See high-throughput economy.

hydrocarbon Organic compound of hydrogen and carbon atoms. The simplest hydrocarbon is methane (CH4), the major component of natural gas.

inductive reasoning Using observations and facts to arrive at generalizations or hypotheses. It goes from the specific to the general and is widely used in science. Compare deductive reasoning.

inorganic compounds All compounds not classified as organic compounds. See organic compounds.

input Matter, energy, or information entering a system. Compare output, throughput.

ion Atom or group of atoms with one or more positive (1) or negative (2) electrical charges. Compare atom, molecule.

ionizing radiation Fast-moving alpha or beta particles or high-energy radiation (gamma rays) emitted by radioisotopes. They have enough energy to dislodge one or more electrons from atoms they hit, forming charged ions in tissue that can react with and damage living tissue. Compare nonionizing radiation.

isotopes Two or more forms of a chemical element that have the same number of protons but different mass numbers because they have different numbers of neutrons in their nuclei.

kilocalorie (kcal) Unit of energy equal to 1,000 calories. See calorie.

kinetic energy Energy that matter has because of its mass and speed or velocity. Compare potential energy.

law of conservation of energy See first law of thermodynamics.

law of conservation of matter In any physical or chemical change, matter is neither created nor destroyed but merely changed from one form to another; in physical and chemical changes, existing atoms are rearranged into different spatial patterns (physical changes) or different combinations (chemical changes).

low-quality energy Energy that is dispersed and has little ability to do useful work. An example is low-temperature heat. Compare high-quality energy.

low-quality matter Matter that is dilute or dispersed or contains a low concentration of a useful resource. Compare high-quality matter.

low-throughput economy Economy based on working with nature by (1) recycling and reusing discarded matter, (2) preventing pollution, (3) conserving matter and energy resources by reducing unnecessary waste and use, (4) not degrading renewable resources, (5) building things that are easy to recycle, reuse, and repair, (6) not allowing population size to exceed the carrying capacity of the environment, and (7) preserving biodiversity. See environmental worldview. Compare high-throughput economy, matter-recycling economy.

low-waste society See low-throughput economy.

mass Amount of material in an object.

mass number Sum of the number of neutrons (n) and the number of protons (p) in the nucleus of an atom. It gives the approximate mass of that atom. Compare atomic number.

material efficiency Total amount of material needed to produce each unit of goods or services. Also called resource productivity. Compare energy efficiency.

matter Anything that has mass (the amount of material in an object) and takes up space. On the earth, where gravity is present, we weigh an object to determine its mass.

matter quality Measure of how useful a matter resource is, based on its availability and concentration. See high-quality matter, low-quality matter.

matter-recycling economy Economy that emphasizes recycling the maximum amount of all resources that can be recycled. The goal is to allow economic growth to continue without depleting matter resources and without producing excessive pollution and environmental degradation. Compare high-throughput economy, low-throughput economy.

metabolism Ability of a living cell or organism to capture and transform matter and energy from its environment to supply its needs for survival, growth, and reproduction.

mixture Combination of one or more elements and compounds.

model Approximate representation or simulation of a system being studied.

molecule Combination of two or more atoms of the same chemical element (such as O2) or different chemical elements (such as H2O) held together by chemical bonds. Compare atom, ion.

natural ionizing radiation Ionizing radiation in the environment from natural sources. See ionizing radiation.

natural law See scientific law.

natural radioactive decay Nuclear change in which unstable nuclei of atoms spontaneously shoot out particles (usually alpha or beta particles) or energy (gamma rays) at a fixed rate.

negative feedback loop Situation in which a change in a certain direction provides information that causes a system to change less in that direction. Compare positive feedback loop.

neutron (n) Elementary particle in the nuclei of all atoms (except hydrogen-1). It has a relative mass of 1 and no electric charge. Compare electron, proton.

Nondegradable pollutant Material that is not broken down by natural processes. Examples are the toxic elements lead and mercury. Compare biodegradable pollutant, degradable pollutant, slowly degradable pollutant.

nonionizing radiation Forms of radiant energy such as radio waves, microwaves, infrared light, and ordinary light that do not have enough energy to cause ionization of atoms in living tissue. Compare ionizing radiation.

nonpersistent pollutant See degradable pollutant.

nuclear change Process in which nuclei of certain isotopes spontaneously change, or are forced to change, into one or more different isotopes. The three principal types of nuclear change are natural radioactivity, nuclear fission, and nuclear fusion. Compare chemical change, physical change.

nuclear energy Energy released when atomic nuclei undergo a nuclear reaction such as the spontaneous emission of radioactivity, nuclear fission, or nuclear fusion.

nuclear fission Nuclear change in which the nuclei of certain isotopes with large mass numbers (such as uranium-235 and plutonium-239) are split apart into lighter nuclei when struck by a neutron. This process releases more neutrons and a large amount of energy. Compare nuclear fusion.

nuclear fusion Nuclear change in which two nuclei of isotopes of elements with a low mass number (such as hydrogen-2 and hydrogen-3) are forced together at extremely high temperatures until they fuse to form a heavier nucleus (such as helium-4). This process releases a large mount of energy. Compare nuclear fission.

nucleus Extremely tiny center of an atom, making up most of the atom's mass. It contains one or more positively charged protons and one or more neutrons with no electrical charge (except for a hydrogen-1 atom, which has one proton and no neutrons in its nucleus).

open system System, such as a living organism, in which both matter and energy are exchanged between the system and the environment. Compare closed system.

organic compounds Compounds containing carbon atoms combined with each other and with atoms of one or more other elements such as hydrogen, oxygen, nitrogen, sulfur, phosphorus, chlorine, and fluorine. All other compounds are called inorganic compounds.

output Matter, energy, or information leaving a system. Compare input, throughput.

persistence How long a pollutant stays in the air, water, soil, or body. See also inertia.

persistent pollutant See slowly degradable pollutant.

pH Numeric value that indicates the relative acidity or alkalinity of a substance on a scale of 0-14, with the neutral point at 7. Acid solutions have pH values lower than 7, and basic or alkaline solutions have pH values greater than 7.

physical change Process that alters one or more physical properties of an element or a compound without altering its chemical composition. Examples are changing the size and shape of a sample of matter (crushing ice and cutting aluminum foil) and changing a sample of matter from one physical state to another (boiling and freezing water). Compare chemical change, nuclear change.

plasma An ionized gas consisting of electrically conductive ions and electrons. It is known as a fourth state of matter.

positive feedback loop Situation in which a change in a certain direction provides information that causes a system to change further in the same direction. Compare negative feedback loop.

potential energy Energy stored in an object because of its position or the position of its parts. Compare kinetic energy.

precision Measure of reproducibility, or how closely a series of measurements of the same quantity agree with one another. Compare accuracy.

proton (p) Positively charged particle in the nuclei of all atoms. Each proton has a relative mass of 1 and a single positive charge. Compare electron, neutron.

radiation Fast-moving particles (particulate radiation) or waves of energy (electromagnetic radiation). See alpha particle, beta particle, gamma rays.

radioactive decay Change of a radioisotope to a different isotope by the emission of radioactivity.

radioactive isotope See radioisotope.

radioactivity Nuclear change in which unstable nuclei of atoms spontaneously shoot out

"chunks" of mass, energy, or both at a fixed rate. The three principal types of radioactivity are gamma rays and fast-moving alpha particles and beta particles.

radioisotope Isotope of an atom that spontaneously emits one or more types of radioactivity (alpha particles, beta particles, gamma rays).

resource productivity See material efficiency.

science Attempts to discover order in nature and use that knowledge to make predictions about what should happen in nature. See consensus science, frontier science, scientific data, scientific hypothesis, scientific law, scientific methods, scientific model, scientific theory.

scientific data Facts obtained by making observations and measurements. Compare scientific hypothesis, scientific law, scientific methods, scientific model, scientific theory.

scientific hypothesis Educated guess that attempts to explain a scientific law or certain scientific observations. Compare scientific data, scientific law, scientific methods, scientific model, scientific theory.

scientific law Description of what scientists find happening in nature repeatedly in the same way, without known exception. See first law of thermodynamics, law of conservation of matter, second law of thermodynamics. Compare scientific data, scientific hypothesis, scientific methods, scientific model, scientific theory.

scientific methods Ways that scientists gather data and formulate and test scientific hypotheses, models, theories, and laws. See scientific data, scientific hypothesis, scientific law, scientific model, scientific theory.

scientific model Simulation of complex processes and systems. Many are mathematical models that are run and tested using computers.

scientific theory Well-tested and widely accepted scientific hypothesis. Compare scientific data, scientific hypothesis, scientific law, scientific methods, scientific model.

second law of thermodynamics In any conversion of heat energy to useful work, some of the initial energy input is always degraded to a lower-quality, more dispersed, less useful energy, Usually low-temperature heat that flows into the environment; you cannot break even in terms of energy quality. See first law of thermodynamics.

slowly degradable pollutant Material that is slowly broken down into simpler chemicals or reduced to acceptable levels by natural physical, chemical, and biological processes. Compare biodegradable pollutant, degradable pollutant, nondegradable pollutant.

storage area Place within a system where energy, matter, or information can accumulate for various lengths of time before being released. Compare input, output, throughput.

subatomic particles Extremely small particles--electrons, protons, and neutrons--that make up the internal structure of atoms.

sustainability Ability of a system to survive for some specified (finite) time.

Synergistic interaction Interaction of two or more factors or processes so the combined effect is greater than the sum of their separate effects.

synergy See synergistic interaction.

system Set of components that function and interact in some regular and theoretically predictable manner.

temperature Measure of the average speed of motion of the atoms, ions, or molecules in a substance or combination of substances at a given moment. Compare heat.

throughput Rate of flow of matter, energy, or information through a system. Compare input, output.

throwaway society See high-throughput economy.

time delay Time lag between the input of a stimulus into a system and the response to the stimulus.