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atomic theory

explanation of the structure of matter in terms of different combinations of very small particles


minute particle of which matter is composed; the smallest part of an element that can enter into chemical reaction


type of matter composed of atoms of two or more elements chemically combined in fixed proportions

chemical reaction

rearrangement of atoms present in reacting substances to give new chemical combinations present in the substances formed

law of multiple proportions

when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in ratios of small whole numbers

atomic symbol

one- or two-letter notation used to represent an atom corresponding to a particular element


positively charged central core of an atom; contains most of the atom's mass


very light, negatively charge particle that exists in the region around the positively charged nucleus


negative electrode


positive electrode

cathode rays

rays that originate from the cathode, or negative electrode, in a gas-discharge tube

coulomb (C)

unit of electric charge

nuclear model

most of the mass of an atom is concentrated in a positively charged center, called the nucleus, around which negatively charge electrons move


nuclear particle having a positive charge equal to +e (e being the charge on an electron) and a mass more than 1800 times that of an electrons

atomic number (Z)

number of protons in an atomic nucleus; identifies the element


substance whose atoms all have the same atomic number


neutral particle of mass almost identical to that of a proton, but without electric charge

mass number (A)

total number of protons and neutrons in a nucleus


an atom characterized by a definite atomic number and mass number

nuclide symbol

symbol for a nuclide in which the mass number is written as a superscript and the atomic number as a subscript on the left of the symbol for the element


atoms whose nuclei have the same atomic number but different mass number

mass spectrometer

instrument used to determine atomic mass

atomic mass unit (amu)

mass unit equal to exactly one-twelfth the mass of a carbon-12 atom

atomic weight

average atomic mass for the naturally occurring element, expressed in atomic mass units

mass spectrum

chart recording from the mass spectrometer that shows the relative number of atoms for various masses

fractional abundance

fraction of the total number of atoms that is composed of a particular isotope

periodic table

tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements

period (of periodic table)

elements in any one horizontal row of the periodic table

group (or periodic table)

elements in any one column of the periodic table

main-group (representative) elements

elements in the A groups of the periodic table

transition elements

elements in the B groups of the periodic table

inner-transition elements

two rows of elements at the bottom of the periodic table


first of the two rows of inner-transition elements


second of the rows of inner-transition elements

alkali metals

elements in Group IA of the periodic table


elements in Group VIIA of the periodic table


substance or mixture that has a characteristic luster or shine and is generally a good conductor of heat and electricity; elemental metals are to the left of the staircase line on the periodic table


able to be hammered into sheets


able to be drawn into wire


element to the right of the staircase line on the periodic table; exhibits characteristics different from those of metals

metalloid (semimetal)

element bordering the staircase line on the periodic table; exhibits both metallic and nonmetallic properties


elements that, when pure, are poor conductors of electricity at room temperature but become good conductors at higher temperatures


adding small amounts of other element to pure semiconductor elements to make them very good electrical conductors

chemical formula

notation that uses atomic symbols with numerical subscripts to convey the relative proportions of atoms of the different elements in the substance


definite group of atoms that are chemically bonded together and, as a group, electrically neutral

molecular substance

substance composed of molecules of all which are alike

molecular formula

gives the exact number of different atoms of an element in a molecule

structural formula

chemical formula that shows which atoms are bonded to one another in a molecule


very large molecules that are made up of a number of smaller molecules repeatedly linked together


the small molecules that are linked together to form a polymer


electrically charged particle obtained from an atom or chemically bonded group of atoms by addition or removal of one or more electrons


negatively charged ion


positively charged ion

ionic compound

compound composed of cations and anions


solid having a regular three-dimensional arrangement of either ions, atoms, or molecules

formula unit

group of atoms or ions explicitly symbolized in the chemical formula

organic compounds

molecular substance that contain carbon


compounds containing only hydrogen and carbon

functional groups

reactive portion of a molecule that undergoes predictable reaction


molecule that contains an —OH functional group


organic molecule that contains an oxygen atom between two carbon atoms

chemical nomenclature

systematic naming of chemical compounds

organic compounds

molecular substances that contain carbon combined with other elements, such as hydrogen, oxygen, and nitrogen

inorganic compounds

compounds composed of elements other than carbon

monatomic ion

ion formed from a single atom

Stock system

system for naming compounds in which a Roman numeral within parentheses follows the first-named element ot indicate its charge or oxidation number

oxidation stare or oxidation number

hypothetical charge assigned in accordance with certain rules; denoted with a Roman numeral following the name of the metal atom


in an older system of nomenclature, a suffix added to the stem name of an element to indicate the cation of lower charge; also indicates the oxoacid with fewer oxygen atoms


in an older system of nomenclature, a suffix added to the stem name of an element to indicate the cation of higher charge; indicates the oxoacid with more oxygen atoms; also indicates an acid solution obtained from binary compounds of hydrogen and nonmetals


suffix added to the stem name of the element to name monatomic anions or the more electronegative element in binary compounds

polyatomic ion

ion consisting of two or more atoms chemically bonded together and carrying a net electric charge

oxoanion (oxyanion)

anion composed of oxygen with another element, which is the central element


molecular compound that can yield one or more hydronium ions, H3O+, an an anion for each acid molecule when the acid dissolves in water


acid containing hydrogen, oxygen, and another element


suffix denoting the oxoanion with the greater number of oxygen atoms


suffix denoting the oxoanion with the lesser number of oxygen atoms


prefix denoting the oxoacid or oxoanion with the least number of oxygen atoms in the series


prefix denoting the oxoacid or oxoanion with the greatest number of oxygen atoms in the series

acid anions

anions that have hydrogen atoms they can lose as hydronium ions, H3O+


Greek prefix meaning two


prefix meaning an oxygen in the root ion name has been replaced by a sulfur atom

binary compound

compound composed of only two elements


prefix added to the stem name of the nonmetal to name the acid solution obtained from binary compound of hydrogen and nonmetals


compound that contains water molecules weakly bound in its crystals

chemical equation

symbolic representation of a chemical reaction in terms of chemical formulas


starting substance in a chemical reaction; appears to the left of the arrow in a chemical reaction


substance that results form a chemical reaction; appears to the right of the arrow in a chemical equation


number that appears in front of a formula in a chemical equation and gives the relative number of molecules or formula units of a substance involved in the reaction


phase label placed after a formula in a chemical equation to indicate that the substance is a gas


phase label placed after a formula in a chemical equation to indicate that the substance is a liquid


phase label placed after a formula in a chemical equation to indicate that the substance is a solid


phase label placed after a formula in a chemical equation to indicate that the substance is in aqueous (water) solution


substance that speeds up a reaction without undergoing any net change itself


describes a chemical equation having correct coefficients

balancing by inspection

trial-and-error method of balancing a chemical equation by writing appropriate coefficient until there is the same number of any one elemental atom on each side of the arrow

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