A
absolute zero The temperature defined as 0 K on the Kelvin scale and –273.15 °C on the Celsius scale. Considered to be the lowest possible temperature that matter can reach. (p. 279)
absorption Of light, not being transmitted because certain colors are removed by an object. Absorption transfers energy back to the object. (p. 579)
acid A substance that adds hydrogen ions, H+, to an aqueous solution; a substance that donates a proton to another substance in solution. (p. 430)
actinides A series of elements that follow actinium in Period 7 of the periodic table and that are typically placed separately at the bottom of the periodic table. (p. 44)
activation energy The minimum amount of energy required to initiate a chemical process or reaction. (p. 537)
activity series A table showing elements in order of their chemical activity, with the most easily oxidized at the top of the list. (p. 564)
actual yield The amount of a product obtained when a reaction is run (as opposed to the theoretical yield). (p. 473)
air mass A large volume of air that has consistent temperature and water content. (p. 288)
alkali metals The elements in Group 1A on the periodic table, except for hydrogen. (p. 44)
alkaline earth metals The elements in Group 2A on the periodic table. (p. 44)
G-2
alpha decay A nuclear reaction in which an atom emits an alpha particle consisting of two protons and two neutrons. Alpha decay decreases the atomic number of an atom by 2 and the mass number by 4. (p. 72)
alpha particle A particle made of two protons and two neutrons, equivalent to the nucleus of a helium atom. (p. 72)
amino acid A molecule that contains both an amine (–NH2) and a carboxylic acid (–COOH) functional group. (p. 247)
anion An ion that has a negative charge. (p. 96)
aqueous solution A solution in which water is the dissolving medium or solvent. (p. 25)
Arrhenius theory of acids and bases An acid-base theory that defines an acid as a substance that adds hydrogen ions, H+, to an aqueous solution, and a base as a substance that adds hydroxide ions, OH–, to an aqueous solution. (p. 434)
atmosphere (atm) A unit of measurement for gas pressure. One atmosphere is equivalent to 14.7 pounds of pressure per square inch or a barometric reading of 760 millimeters of mercury. (p. 301)
atmospheric pressure Pressure exerted by the weight, or force, of the air pressing down on a surface. Air pressure is a result of air molecules colliding with the surfaces of objects on Earth. At sea level, atmospheric pressure equals approximately 1 atm or 14.7 lb/in2. (p. 301)
atom The smallest unit of an element that retains the chemical properties of that element and can exist as a separate particle. (p. 51)
atomic mass The mass of a single atom (or isotope) of an element. (p. 38)
atomic mass unit (amu) The unit used for expressing atomic mass. 1 amu = 1.66 × 10–24 g, the mass of one hydrogen atom. This is 1/12 the mass of a carbon-12 atom. (p. 38)
G-3
atomic number The consecutive whole numbers associated with the elements on the periodic table. The atomic number is equal to the number of protons in the atomic nucleus of an element. (p. 41)
atomic theory A theory that states that all matter is made up of individual particles called atoms. (p. 52)
average atomic mass The weighted average of the mass of the isotopes of an element. (p. 62)
Avogadro’s law A scientific law stating that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. (p. 333)
Avogadro’s number A number equal to 6.02 × 1023. It is the number of particles (atoms, ions, molecules, or formula units) present in one mole of a substance. (p. 332)
B
ball-and-stick model A three-dimensional representation of a molecule that uses color-coded balls to represent atoms and sticks to represent bonds. (p. 186)
base A substance that adds hydroxide ions OH–, to an aqueous solution, or a substance that accepts protons, H+ ions, from another substance in solution. (p. 430)
bent shape The nonlinear shape around a bonded atom with two lone pairs of electrons. (p. 194)
beta decay A nuclear reaction in which a neutron changes into a proton and an electron, and the atom emits a beta particle, which is the electron. Beta decay increases the atomic number of the atom without changing the mass. (p. 72)
beta particle An electron emitted from the nucleus of an atom during beta decay. (p. 72)
boiling point (boiling temperature) The temperature at which both liquid and gas phases of a single substance are present and in equilibrium; the temperature at which equilibrium is established between a liquid and its vapor at a pressure of 1 atm.
G-4
(p. 274)
bond energy The amount of energy that is required to break a specific chemical bond. (p. 531)
bonded pair A pair of electrons that are shared in a covalent bond between two atoms. (p. 163)
Boyle’s law The scientific law that states that the volume of a given sample of gas at a given temperature is inversely proportional to its pressure. (p. 306)
Brønsted-Lowry theory of acids and bases An acid-base theory that defines an acid as a substance that donates a proton to another substance, and a base as a substance that accepts a proton from another substance. (p. 434)
C
calorie (cal) A unit of measurement for thermal energy. The amount of heat required to raise the temperature of 1 gram of water by 1 Celsius degree. A kilocalorie, 1000 calories, is equal to one food Calorie. (p. 497)
calorimetry A procedure used to measure the heat transfer that occurs as a result of chemical reactions or physical changes. (p. 517)
catalyst A substance that accelerates a chemical reaction but is itself not permanently consumed or altered by the reaction. (p. 181)
cation An ion that has a positive charge. (p. 96)
Charles’s law The law that states that the volume of a given sample of gas is proportional to its Kelvin temperature if the pressure is unchanged. (p. 284)
chemical bond An attraction between atoms that holds them together. (p. 129)
chemical change See chemical reaction.
chemical equation A representation of a chemical reaction written with chemical symbols and formulas. (p. 179)
chemical equilibrium A dynamic state in which opposing processes occur at the same time and the rate of the forward process is equal to the rate of the reverse process. (p. 620)
G-5
chemical formula A combination of element symbols and numbers representing the composition of a chemical compound. (p. 24)
chemical reaction (chemical change) A transformation that alters the composition of one or more substances such that one or more new substances with new properties are produced. (p. 28)
chemical symbol A one- or two-letter representation of an element. The first letter is always uppercase. If there is a second letter, it is lowercase. (p. 24)
chemistry The study of substances, their properties, and how they can be transformed; the study of matter and how it can be changed. (p. 8)
coefficients The numbers in front of the chemical formulas of the reactants and products in a balanced chemical equation. They indicate the correct ratio in which the reactants combine to form the products. (p. 372)
combination reaction A reaction in which two or more reactants combine to form a single product. (p. 375)
combined gas law The law that describes the proportional relationship among the pressure, temperature, and volume of a gas. It states that the value of PV/T will be constant for a given sample of any gas. (p. 318)
combustion An exothermic chemical reaction between a fuel and oxygen, often producing flames; burning. (p. 513)
complete ionic equation A chemical equation that shows all of the soluble ionic compounds as independent ions. (p. 459)
compound A pure substance that is a chemical combination of two or more elements in a specific ratio. (p. 24)
concentration A measure of the amount of solute dissolved per unit of volume of solution, often expressed as moles of solute per liter of solution, mol/L. (p. 410)
G-6
conductivity A property that describes how well a substance transmits electricity, heat, or sound. (p. 125)
core electrons All electrons in an atom that are not valence electrons. (p. 93)
covalent bonding A type of chemical bonding in which one or more pairs of valence electrons are shared between the atoms. (p. 130)
D
daughter isotope An isotope that is formed as a result of a nuclear reaction. (p. 78)
decomposition reaction A chemical change in which a single substance is broken down into two or more simpler substances. (p. 376)
density The measure of the mass of a substance per unit of volume, often expressed as grams per milliliter, g/mL, or grams per cubic centimeter, g/cm3. (p. 17)
diatomic molecule A molecule consisting of two atoms. (p. 228)
dilution The process of adding solvent to a solution to lower the concentration of solute. (p. 442)
dipole A molecule or covalent bond with a nonsymmetrical distribution of electrical charge that makes the molecule or bond polar. (p. 224)
dissociate To break apart to form ions in solution. (p. 433)
dissolve To disperse a substance homogeneously into another substance at the molecular, ionic, or atomic level. (p. 125)
double bond A covalent bond where four electrons are shared between two atoms. (p. 166)
double exchange reaction (double displacement reaction) A chemical change in which both reactants break apart and then recombine to form two new products; chemical change where there is an exchange of ions between reactants to form new products. (p. 377)
G-7
E
electrochemical cell A device used for generating electrical energy from chemical reactions. The electrical current is caused by substances releasing and accepting electrons in oxidation-reduction reactions. (p. 570)
electrolyte solution A solution that contains ions and can conduct electricity. (p. 569)
electromagnetic radiation A large range of waves, some visible, some invisible, all traveling at the speed of light, in a vacuum, and at widely varying wavelengths and frequencies. (p. 586)
electron An elementary particle with a negative charge that is located outside of the nucleus of an atom. It has a mass of about 1/1838 amu. (p. 54)
electron configuration A notation for keeping track of where the electrons in an atom are distributed among the shells and subshells in an atom. (p. 117)
electron domain The space occupied by bonded pairs or lone pairs of valence electrons in a molecule. Electron domains affect the overall shape of a molecule. (p. 192)
electron domain theory A scientific theory that states that every electron domain is located as far away as possible from every other electron domain in a molecule. (p. 193)
electronegativity A measure of the ability of an atom in a molecular substance to attract electrons to itself. (p. 224)
electroplating The process by which a material is coated with a thin layer of metal using electricity passed through a suitable ionic solution. (p. 136)
element A unique substance that cannot be broken down into simpler substances through physical or chemical processes. Elements serve as the building materials of all matter. (p. 24)
emission In general, transmission of energy from a source. Of light, a transmission of energy from the Sun or other bright body. (p. 576)
G-8
endothermic Describes a process in which heat transfers from the surroundings to the system; heat-absorbing. (p. 487)
energy A measure of the capacity of an object or system to do work or produce heat. (p. 483)
entropy The tendency of energy or matter in a system to disperse; the energy of a system that cannot be used for external work. (p. 492)
equilibrium constant K A measure of whether starting substances or products are favored in an equilibrium mixture. A large value for K indicates a large amount of product. A small value for K indicates very little product. (p. 627)
equilibrium-constant equation A specific mathematical relationship between K and the concentrations of starting substances and products in an equilibrium mixture. (p. 631)
equivalence point The point in an acid-base titration when the acid and base have completely neutralized each other. (p. 451)
evaporation The phase change from a liquid to a gas. (p. 297)
exothermic Describes a process in which heat is transferred from a system to the surroundings; heat-releasing. (p. 484)
extensive property A characteristic, such as volume or mass, that is specific to the amount of matter and therefore changes if the quantity of the substance changes. (p. 19)
F
first law of thermodynamics The scientific law that states that energy is conserved; therefore it cannot be created or destroyed. (p. 492)
fission (nuclear) The splitting apart of an atomic nucleus into two smaller nuclei, accompanied by a release of energy. (p. 74)
G-9
flame test A laboratory procedure used to determine the presence of certain metal atoms in a chemical sample by heating the sample in a flame and observing the resulting flame color. (p. 85)
formula unit The simplest chemical formula that can be used to represent network covalent or ionic compounds that shows the elements present in the smallest whole number ratio. (p. 372)
frequency The number of waves that pass by a certain point in space per second, abbreviated as f. The frequency of light is measured in hertz, Hz. (p. 582)
functional group A structural feature of a molecule; consists of a specific arrangement of atoms, responsible for certain properties of the compound. (p. 170)
fusion (nuclear) The joining of two atomic nuclei to form a larger nucleus, accompanied by a release of energy. (p. 75)
G
gamma ray Electromagnetic radiation with the shortest wavelengths, less than 10–11 m. Emitted when a nucleus decays or during a nuclear explosion. Used in irradiation of food and in some cancer treatments. (p. 74)
Gay-Lussac’s law The scientific law that states that the pressure of a given amount of gas is directly proportional to temperature, if the gas volume does not change. (p. 310)
group A vertical column on the periodic table, also called a family. Elements in a group have similar properties. (p. 44)
H
half-cell One-half of an electrochemical cell, the site of either oxidation or reduction. (p. 570)
half-life The amount of time required for one-half of the radioactive atoms in a sample to decay. (p. 73)
G-10
half-reaction A chemical equation that represents either the oxidation or the reduction part of an oxidation-reduction reaction. (p. 570)
halogens The elements in Group 7A on the periodic table. (p. 44)
heat A transfer of energy between two substances, from a hotter body to a colder body. (p. 486)
heat of combustion The energy released as heat when a compound undergoes complete combustion with oxygen, usually expressed per mole of the fuel. (p. 524)
heat of formation The energy transferred as heat during a chemical reaction when a compound is formed from its constituent elements, expressed per mole of product. (p. 554)
heat of fusion The amount of heat transfer required to change a substance from a solid to a liquid, usually expressed per mole or gram. (p. 506)
heat of reaction The amount of energy transferred as heat during a chemical reaction. (p. 524)
heat of vaporization The amount of heat transfer required to change a substance from a liquid to a gas, usually expressed per mole or gram. (p. 506)
heterogeneous mixture A mixture whose composition is not uniform throughout. (p. 410)
homogeneous mixture A mixture whose composition is uniform throughout. (p. 410)
HONC 1234 rule A rule that states that in most molecules, hydrogen makes 1 bond, oxygen makes 2 bonds, nitrogen makes 3 bonds, and carbon makes 4 bonds. (p. 156)
humidity The concentration of the water vapor in the air at any given time. (p. 340)
G-11
hydrogen bond An intermolecular attraction between a hydrogen atom in a molecule and an electronegative atom in another molecule (especially nitrogen, oxygen, or fluorine). The hydrogen atoms in water molecules form hydrogen bonds with the oxygen atoms in other water molecules. (p. 503)
hypothesis A proposed explanation for an observation or scientific problem, which can be tested by further investigation. (p. 7)
I
ideal gas law The scientific law that relates volume, pressure, temperature, and the number of moles of a gas sample: PV = nRT, where R is the universal gas constant. (p. 337)
indicator (acid-base) A chemical compound that indicates the relative acidity or basicity of a solution through its characteristic color changes. (p. 429)
infrared radiation Electromagnetic radiation with longer wavelengths than those of visible light, from 10–3 m to 10–6 m. Causes molecules to vibrate, which human beings sense as heat. Abbreviated as IR radiation. (p. 587)
insoluble Unable to be dissolved in another substance. (p. 125)
intensive property A characteristic, such as boiling point or density, that does not depend on the size or amount of matter and can be used to identify matter. (p. 19)
intermolecular force A force of attraction that occurs between molecules. (p. 216)
inversely proportional Related in such a way that when one quantity increases, the other decreases in a mathematically predictable way. The variables x and y are inversely proportional to each other if y = k/x, where k is the proportionality constant. (p. 306)
ion An atom or group of bonded atoms that has a positive or negative charge. (p. 95)
G-12
ionic bonding A type of chemical bonding that is the result of the transfer of electrons from one atom to another, typically between metal and nonmetal atoms. (p. 130)
ionic compound A compound that consists of positively charged metal cations and negatively charged nonmetal anions formed when valence electrons are transferred. (p. 98)
isomers Compounds with the same molecular formula but different structural formulas. Isomers differ in molecular structure and in chemical and physical properties. (p. 152)
isotopes Atoms of the same element that have different numbers of neutrons. These atoms have the same atomic number but different mass numbers. (p. 62)
J
joule (J) A unit of measurement of energy. One calorie is equal to 4.184 joules. (p. 524)
K
Kelvin scale A temperature scale with units in kelvins, K, that sets the zero point at –273.15 °C, which is also known as absolute zero. Kelvin units are equivalent in scale to Celsius units. (p. 279)
kinetic energy The energy of motion. (p. 488)
kinetic theory of gases The scientific theory that states that gases are composed of tiny particles in continuous, random, straight-line motion and collide with each other and the walls of the container. (p. 280)
L
lanthanides A series of elements that follow lanthanum in Period 6 of the periodic table; they are typically placed separately at the bottom of the periodic table. (p. 44)
law of conservation of mass The scientific law that states that mass cannot be gained or lost in a chemical reaction and that matter cannot be created or destroyed. (p. 34)
G-13
Le Châtelier’s principle An experimental observation that, when a stress is put on a system at equilibrium, the system responds by reducing the effect of the change. (p. 643)
Lewis dot structure A diagram that shows a molecule’s structure by using dots to represent the valence electrons. (p. 162)
Lewis dot symbol A diagram that uses dots to represent the valence electrons of a single atom. (p. 162)
light detector A device that senses electromagnetic radiation, such as a radio or a photovoltaic cell. (p. 593)
light ray A model of light that shows the straight-line path that light travels and how a beam of light interacts with matter. (p. 577)
light wave Ripples of light energy created by forces that oscillate up and down, radiating in space from a source, such as the Sun. (p. 582)
limiting reactant The reactant that runs out first in a chemical reaction. It is the reactant that limits the amount of product that can be produced in the reaction. (p. 464)
linear shape A straight-line shape found in small molecules. (p. 197)
lone pair A pair of unshared valence electrons that are not involved in bonding in a molecule. (p. 163)
M
main group elements The elements in Groups 1A to 7A on the periodic table. (p. 44)
mass A measure of the quantity of matter in an object. (p. 9)
mass number The sum of the number of protons and neutrons in the nucleus of an atom. (p. 62)
matter Anything that has substance and takes up space; anything that has mass and volume. (p. 9)
G-14
melting point (melting temperature) The temperature at which both solid and liquid phases of a single substance can be present and in equilibrium. (p. 274)
meniscus The curvature of the top of a liquid in a container, which is the result of intermolecular attractions between the liquid and the container. (p. 12)
metal An element that is generally shiny and malleable and an excellent conductor of heat and electricity. Metals are located to the left of the stairstep line on the periodic table. (p. 45)
metallic bonding A type of bonding between metal atoms in which the valence electrons are free to move throughout the substance. (p. 130)
metalloid An element that has properties of both metals and nonmetals. Metalloids are located along the stair-step line of the periodic table. (p. 46)
microwave radiation Electromagnetic radiation with wavelengths longer than visible light and infrared radiation from 1 m to 10–3 m. Absorption of these waves cooks food. (p. 587)
mirror-image isomer Molecules whose structures are mirror images of each other and cannot be superimposed on one another. (p. 243)
mixture A blend of two or more substances that are not chemically combined. (p. 24)
model A simplified representation of a real object or process that facilitates understanding or explanation of that object or process. (p. 52)
molarity The concentration of dissolved substances in a solution, expressed in moles of solute per liter of solution. (p. 410)
molar mass The mass in grams of one mole of a substance. (p. 391)
mole A counting unit used to keep track of large numbers of particles. One mole represents 6.02 × 1023 items. (p. 332)
mole ratio The ratio of the moles of one reactant or product to the moles of another reactant or product in a balanced chemical equation. (p. 463)
G-15
molecular covalent bonding A type of chemical bonding characterized by the sharing of valence electrons between atoms, resulting in individual units called molecules. (p. 130)
molecular formula The chemical formula of a molecular substance, showing the identity of the atoms in each molecule and the ratios of those atoms to one another. (p. 148)
molecule A group of atoms that are covalently bonded together. (p. 131)
monatomic ion An ion that consists of only one atom. (p. 109)
N
net ionic equation A chemical equation that is written without including spectator ions. (p. 460)
network covalent bonding A type of chemical bonding characterized by the sharing of valence electrons throughout the entire solid sample. (p. 130)
neutralization reaction A chemical reaction in which an acid and base react to form a salt and water. (p. 448)
neutron A particle that is located in the nucleus of an atom and does not have an electric charge. The mass of a neutron is almost exactly equal to that of a proton, about 1 amu. (p. 54)
noble gases The elements in Group 8A on the periodic table. Noble gases are known for not being reactive. (p. 44)
nonmetal An element that does not exhibit metallic properties. Nonmetals are often gases or brittle solids at room temperature. Nonmetals are poor conductors of heat and electricity and are located to the right of the stair-step line on the periodic table. (p. 45)
nonpolar molecule A molecule that is not attracted to an electrical charge. A molecule is nonpolar if each atom shares electrons equally or there is no net dipole in the molecule. (p. 215)
G-16
nuclear chain reaction A nuclear reaction in which neutrons emitted from the nucleus during fission strike surrounding nuclei, causing them to split apart as well. (p. 79)
nuclear equation A representation of a nuclear reaction written with isotope symbols. (p. 78)
nuclear reaction A process that changes the energy, composition, or structure of an atom’s nucleus. (p. 71)
nucleus The dense, positively charged structure composed of protons and neutrons that is found in the center of an atom. (p. 54)
number density The number of gas particles per unit volume usually expressed in moles per liter or moles per cubic centimeter. (p. 328)
O
octet rule Nonmetal atoms combine by sharing electrons so that each atom has a total of eight valence electrons. After bonding, each atom resembles a noble gas in its electron arrangements. (p. 165)
opaque Not capable of transmitting light and, therefore, an object or surface not possible to see through. (p. 578)
oxidation A chemical reaction in which an atom or ion loses electrons. Oxidation is always accompanied by reduction. (p. 552)
oxidation-reduction reaction A chemical reaction that involves electron transfer. (p. 560)
P
parent isotope A radioactive isotope that undergoes decay. (p. 78)
partial charge A less than full charge on part of a molecule, created by the unequal sharing of electrons. Partial charges are represented with the symbol delta (δ+ for partial positive charge and δ– for partial negative charge). (p. 215)
partial pressure The pressure exerted by one gas in a mixture of nonreacting gases. The partial pressures of all the gases add up to the total pressure exerted by that mixture of gases. (p. 341)
G-17
peptide bond The bond between two amino acids; also called an amide bond. (p. 249)
percent error A calculation used to find the accuracy of a measurement. The lower the percent error, the more accurate the measurement. (p. 388)
percent yield A calculation that expresses the success of a chemical process in terms of product yield; the ratio of the actual yield to the theoretical yield expressed as a percentage. (p. 473)
period The elements in a horizontal row on the periodic table. (p. 44)
periodic table of the elements A table with elements organized in order of increasing atomic number and grouped such that elements with similar properties are in vertical columns. (p. 39)
pH scale A logarithmic scale describing the concentration of hydrogen ions, H+, in solution. pH = –log [H+]. (p. 430)
phase The physical form of matter such as the solid, liquid, or gaseous state. (p. 25)
phase change A transition between solid, liquid, or gaseous states of matter. (p. 260)
photon A particle of light; one of many separate particles in a beam of light. (p. 590)
physical change A change that alters the form of a substance but does not change the chemical identity of a substance. (p. 259)
pigment A substance that is colored because of the light it reflects. Pigments reflect only a certain color instead of all the colors in white light from the source. (p. 609)
Planck’s constant A mathematical relationship of the frequency of the electromagnetic wave to its energy. Given the symbol, h, and defined as h = 6.63 × 10–34 J · s. (p. 589)
polar molecule A molecule that has a negatively charged end and a positively charged end due to electronegativity differences between the atoms and/or the asymmetry of its structure. (p. 215)
G-18
polyatomic ion An ion that consists of two or more atoms covalently bonded. (p. 109)
potential energy Energy that is stored within a system and can be converted into other types of energy. This energy may be associated with the composition of a substance or its location. (p. 536)
precipitate A solid produced in a chemical reaction between two solutions. (p. 457)
precipitation reaction A chemical reaction that results in the formation of a solid substance (a precipitate) that separates out of a solution because it is not very soluble. (p. 457)
pressure Force applied over a specific area. Force per unit area. (p. 299)
product A substance produced as the result of a chemical reaction. (p. 180)
property A characteristic or quality of a substance. (p. 7)
proportional Related such that when one quantity increases, the other also increases. Two variables are proportional when you can multiply one variable by a constant to obtain the other. The variable y is proportional to the variable x if y = kx where k is the proportionality constant. (p. 265)
proportionality constant The number that relates two variables that are proportional to one another. It is often represented by k. (p. 265)
protein A large molecule made up of chains of amino acids bonded together. Typical protein molecules consist of more than 100 amino acids. (p. 249)
proton A positively charged particle located in the nucleus of an atom. The mass of a proton is almost exactly equal to that of a neutron, about 1 amu. (p. 54)
pyramidal shape The shape assumed by other bonded atoms around an atom with one lone pair of electrons. (p. 193)
R
radiation Emission of energy as light either in the visible or invisible part of the spectrum. (p. 577)
G-19
radio wave Electromagnetic radiation with very long wavelengths from 105 m to 1 m. Emitted at a television or radio station and used in communications satellites. (p. 587)
radioactive decay Spontaneous disintegration of an atomic nucleus accompanied by the emission of particles and radiation. A radioactive substance will decay with a specific half-life. (p. 71)
radioactive isotope Any isotope that has an unstable nucleus and decays over time. (p. 67)
reactants The starting materials in a chemical reaction that are transformed into products during the reaction. (p. 180)
reactivity The tendency of an element or compound to combine chemically with other substances, as well as the ease or speed of the reaction. (p. 37)
receptor site theory The currently accepted model explaining how specific molecules are detected by the nose. Molecules fit into receptor sites that correspond to the overall shape of the molecule. This stimulates a response in the body. (p. 208)
redox reaction Another name for an oxidation-reduction reaction. (p. 560)
reduction A chemical reaction in which an atom or ion gains electrons. Reduction is always accompanied by oxidation. (p. 559)
reflection The bouncing of light off a surface, allowing it to be seen. (p. 578)
relative humidity The amount of water vapor in the air compared to the maximum amount of water vapor possible for a specific temperature, expressed as a percentage. (p. 341)
reversible process A process that can proceed in both the forward direction to produce products and the opposite direction (reverse direction) to produce starting substances. (p. 613)
G-20
rule of zero charge The rule that states that in an ionic compound, the positive charges on the metal cations and the negative charges on the nonmetal anions add up to zero. (p. 99)
S
saturated solution A solution that contains the maximum amount of solute that can be dissolved in a given amount of solvent at a particular temperature. (p. 411)
scientific notation A shorthand notation used for writing numbers that are very large or very small. In this notation, the number is expressed as a decimal number with one digit to the left of the decimal point, multiplied by an integer power of 10. For example, the number 890,000 is written as 8.9 × 105 in scientific notation. (p. 391)
second law of thermodynamics The scientific law that states that energy tends to disperse or spread out. Thermal energy is always spontaneously transferred from a hotter object to a cooler object. (p. 492)
single bond A covalent bond where two electrons are shared between two atoms. (p. 156)
single exchange reaction (single displacement reaction) A chemical change in which an element is displaced from a compound by a more reactive element. (p. 377)
soluble Capable of being dissolved into another substance. (p. 125)
solute A substance dissolved in a solvent to form a solution. (p. 409)
solution A homogeneous mixture of two or more substances. (p. 409)
solvent A substance in which another substance is dissolved, forming a solution. (p. 409)
space-filling model A three-dimensional representation of a molecule with no space between bonded atoms, as distinct from a ball-and-stick model. (p. 200)
G-21
specific heat capacity The amount of heat required to raise the temperature of 1 gram of a substance by 1 °C. (p. 501)
spectator ion An ion that does not directly participate in a chemical reaction. Spectator ions appear on both sides of a complete ionic equation. (p. 459)
spectrometer A device for capturing electromagnetic radiation to study properties of atoms, molecules, and compounds. (p. 596)
spectroscopy A method of using electromagnetic radiation to study properties of atoms, molecules, and compounds as they interact and as they emit light. (p. 597)
speed of light The speed that light travels in a vacuum. Symbolized as c, the speed of light is 3 × 108 m/s. (p. 583)
standard temperature and pressure (STP) A standard set of conditions at which gases can be measured and compared. Standard pressure is 1 atm and standard temperature is 273 K (0 °C). (p. 332)
stoichiometry The quantitative relationship between amounts (usually moles) of reactants and products in a chemical reaction. (p. 468)
strong acid (or base) An acid (or a base) that dissociates completely in solution. (p. 435)
structural formula A two-dimensional drawing or diagram that shows how the atoms in a molecule are connected. Each line represents a covalent bond. (p. 152)
sublimation The process of changing phase from a solid to a gas without passing through the liquid phase. (p. 295)
surroundings Everything in the universe outside the system being investigated. (p. 487)
synthesis The creation of specific compounds by chemists, through controlled chemical reactions. (p. 176)
system The part of the universe being investigated. (p. 486)
G-22
T
temperature A measure of the average kinetic energy of the atoms and molecules in a sample of matter. (p. 280)
tetrahedral shape The shape defined by the symmetrical distribution of four bonded pairs of electrons around a central atom. (p. 192)
theoretical yield The maximum amount of product that could be produced in a chemical reaction when a limiting reactant is entirely consumed. The value is calculated based on a balanced chemical equation. (p. 473)
thermal energy The total kinetic energy associated with the mass and motions of the particles in a sample of matter measured as heat energy. (p. 495)
thermal equilibrium When two objects in contact with one another reach the same temperature, they are in thermal equilibrium. (p. 492)
titration An analytical procedure used to determine the concentration of an acid or a base. A measured volume of an acid or a base of known concentration is reacted with a sample in the presence of an indicator. (p. 451)
toxicity The degree to which a substance can harm an organism. Toxicity depends on the toxin and the dose in which it is received. (p. 381)
transition elements The elements in Groups 1B to 8B on the periodic table. (p. 44)
transmission Of light, passing through certain kinds of objects. (p. 578)
transparent Of an object, capable of transmitting light, meaning that it is possible to see through the object. (p. 578)
trigonal planar shape A flat triangular shape that is found in small molecules with three electron domains surrounding a central atom. (p. 196)
triple bond A covalent bond in which three electron pairs are shared between two atoms. (p. 167)
G-23
U
ultraviolet radiation Electromagnetic radiation with shorter wavelengths than those of visible light, from 4 × 10–7 m to 10–8 m. Causes sunburn and breaking of chemical bonds. Abbreviated as UV radiation. (p. 588)
universal gas constant, R A number that relates the volume, temperature, pressure and number of moles of gas in the ideal gas law. The value of R is dependent on the units used. One value of R is 0.08206 L · atm/mol · K. (p. 337)
V
valence electrons The electrons located in the outermost electron shell of an atom, which participate in chemical bonding. (p. 90)
valence shell The outermost electron shell in an atom. (p. 90)
visible light Electromagnetic radiation with wavelengths that human beings can see from about 10–6 m to 4 × 10–7 m. The wavelength increases from violet to blue to green to yellow to orange to red. (p. 588)
voltage The electrical potential of an electrochemical cell expressed in volts. (p. 571)
volume The amount of space a sample of matter occupies. (p. 9)
W
water displacement (method) A method for measuring the volume of a solid object by immersing it in water. The volume of the object is equal to the amount of water displaced by the object when fully submerged. (p. 14)
wavelength The distance between two peaks or two troughs of a wave, usually measured in meters. The symbol for wavelength is λ (lambda). (p. 582)
weak acid (or base) An acid (or a base) that does not dissociate completely in solution. (p. 435)
weather The day-to-day atmospheric conditions such as temperature, cloudiness, and rainfall, affecting a specific place. (p. 259)
G-24
white light The mixture of all wavelengths of visible radiation (colors of the rainbow) normally seen as white rays. (p. 578)
work Describes what happens when a force causes an object to move in the direction of the force applied. Work can be calculated as force · distance (p. 544)
X
x-ray Electromagnetic radiation with wavelengths shorter than those of visible light and ultraviolet radiation, from 10–8 m to 10–11 m. Causes electrons to be ejected from atoms and molecules. Used mainly in medical care to create images of bones and teeth. (p. 588)