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| electron dot structure | a notation that depicts valence electrons as dots around the atomic symbol of the element; the symbol represents the inner electrons and atomic nucleus; also called Lewis dot structure |
| ionic compound | a compound composed of positive and negative ions |
| valence electron | an electron in the highest occupied energy level of an atom |
| ionic bond | the electrostatic attraction that binds oppositely charged ions together |
| alloy | a mixture composed of two or more elements, at least one of which is a metal |
| octet rule | atoms react by gaining or losing electrons so as to acquire the stable electron structure of a noble gas, usually eight valence electrons |
| formula unit | the lowest whole-number ratio of ions in an ionic compound; in magnesium chloride, the ratio of magnesium ions to chloride ions is 1:2 and the formula unit is MgCl2 |
| nonpolar covalent bond | a covalent bond in which the electrons are shared equally by the two atoms |
| double covalent bond | a bond in which two atoms share two pairs of electrons |
| molecular formula | a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound |
| polar bond | a covalent bond between atoms in which the electrons are shared unequally |
| triple covalent bond | a covalent bond in which three pairs of electrons are shared by two atoms |
| cation | any atom or group of atoms with a positive charge |
| anion | any atom or group of atoms with a negative charge |
| law of definite proportions | in samples of any chemical compound, the masses of the elements are always in the same proportion |
| law of multiple proportions | whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers |
| polyatomic ion | a tightly bound group of atoms that behaves as a unit and has a positive or negative charge |
| monatomic ion | a single atom with a positive or negative charge resulting from the loss or gain of one or more valence electrons |
| binary compound | a compound composed of two elements; NaCl and Al2O3 are binary compounds |
| chemical formula | an expression that indicates the number and type of atoms present in the smallest representative unit of a substance |
| acid | a compound that produces hydrogen ions in solution; see also hydrogen-ion donor, Lewis acid |
| base | a compound that produces hydroxide ions in solution; see also hydrogen-ion acceptor, Lewis base |
| covalent bond | a bond formed by the sharing of electrons between atoms |
| molecule | a neutral group of atoms joined together by covalent bonds |
| diatomic molecule | a molecule consisting of two atoms |
| molecular compound | a compound that is composed of molecules |
| single covalent bond | a bond formed when two atoms share a pair of electrons |
| structural formula | a chemical formula that shows the arrangement of atoms in a molecule or a polyatomic ion; each dash between a pair of atoms indicates a pair of shared electrons |
| unshared pair | a pair of valence electrons that is not shared between atoms |
| coordinate covalent bond | a covalent bond in which one atom contributes both bonding electrons |
| polyatomic ion | a tightly bound group of atoms that behaves as a unit and has a positive or negative charge |
| bond dissociation energy | the energy required to break the bond between two covalently bonded atoms; this value is usually expressed in kJ per mol of substance |
| resonance structure | one of the two or more equally valid electron dot structures of a molecule or polyatomic ion |
| molecular orbital | an orbital that applies to the entire molecule |
| bonding orbital | a molecular orbital that can be occupied by two electrons of a covalent bond |
| sigma bond | a bond formed when two atomic orbitals combine for form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei |
| pi bond | a covalent bond in which the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms |
| tetrahedral angle | a bond angle of 109.5° that results when a central atom forms four bonds directed toward the center of a regular tetrahedron |
| VSEPR theory | valence-shell electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible |
| hybridization | the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals |
| polar covalent bond | a covalent bond in which the electrons are shared equally by the two atoms |
| polar molecule | a molecule in which one side of the molecule is slightly negative and the opposite side is slightly positive |
| dipole | a molecule that has two poles, or regions, with opposite charges |
| van der Waals forces | the two weakest intermolecular attractions—dispersion interactions and dipole forces |
| dipole interaction | intermolecular forces resulting from the attraction of oppositely charged regions of polar molecules |
| dispersion force | attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces; these are the weakest interactions between molecules |
| hydrogen bond | attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom |
| network solid | a solid in which all of the atoms are covalently bonded to each other |
| halide ion | a negative ion formed when a halogen atom gains an electron |
| coordination number | the number of ions of opposite charge that surround each ion in a crystal |
| metallic bond | the force of attraction that holds metals together; it consists of the attraction of free-floating valence electrons for positively charged metal ions |
| mixture | a physical blend of two or more substances that are not chemically combined |
| heterogeneous mixture | a mixture that is not uniform in composition; components are not evenly distributed throughout the mixture |
| homogeneous mixture | a mixture that is uniform in composition; components are evenly distributed and not easily distinguished |
| solution | a homogeneous mixture; consists of solutes dissolved in a solvent |
| filtration | a process that separates a solid from the liquid in a heterogeneous mixture |
| distillation | a process used to separate components of a mixture using differences in boiling points |
| element | the simplest form of matter that has a unique set of properties; an element cannot be broken down into simpler substances by chemical means |
| compound | a substance that contains two or more elements chemically combined in a fixed proportion |
