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Chemistry LibreTexts

2.9: Key Terms

  • Page ID
    452701
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    Example and Directions
    Words (or words that have the same definition)The definition is case sensitive(Optional) Image to display with the definition [Not displayed in Glossary, only in pop-up on pages](Optional) Caption for Image(Optional) External or Internal Link(Optional) Source for Definition
    (Eg. "Genetic, Hereditary, DNA ...")(Eg. "Relating to genes or heredity")The infamous double helix https://bio.libretexts.org/CC-BY-SA; Delmar Larsen
    Glossary Entries
    Word(s)DefinitionImageCaptionLinkSource
    actinideinner transition metal in the bottom of the bottom two rows of the periodic table    
    alkali metalelement in group 1    
    alkaline earth metalelement in group 2    
    alpha particle (α particle)positively charged particle consisting of two protons and two neutrons    
    anionnegatively charged atom or molecule (contains more electrons than protons)    
    atomic massaverage mass of atoms of an element, expressed in amu    
    atomic mass unit (amu)(also, unified atomic mass unit, u, or Dalton, Da) unit of mass equal to of the mass of a 12C atom    
    atomic number (Z)number of protons in the nucleus of an atom    
    binary acidcompound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)    
    binary compoundcompound containing two different elements.    
    cationpositively charged atom or molecule (contains fewer electrons than protons)    
    chalcogenelement in group 16    
    chemical symbolone-, two-, or three-letter abbreviation used to represent an element or its atoms    
    covalent bondattractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms    
    covalent compound(also, molecular compound) composed of molecules formed by atoms of two or more different elements    
    Dalton (Da)alternative unit equivalent to the atomic mass unit    
    Dalton’s atomic theoryset of postulates that established the fundamental properties of atoms    
    electronnegatively charged, subatomic particle of relatively low mass located outside the nucleus    
    empirical formulaformula showing the composition of a compound given as the simplest whole-number ratio of atoms    
    fundamental unit of charge(also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 10−19 C    
    groupvertical column of the periodic table    
    halogenelement in group 17    
    hydratecompound containing one or more water molecules bound within its crystals    
    inert gas(also, noble gas) element in group 18    
    inner transition metal(also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide    
    ionelectrically charged atom or molecule (contains unequal numbers of protons and electrons)    
    ionic bondelectrostatic forces of attraction between the oppositely charged ions of an ionic compound    
    ionic compoundcompound composed of cations and anions combined in ratios, yielding an electrically neutral substance    
    isomerscompounds with the same chemical formula but different structures    
    isotopesatoms that contain the same number of protons but different numbers of neutrons    
    lanthanideinner transition metal in the top of the bottom two rows of the periodic table    
    law of constant composition(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass    
    law of definite proportions(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass    
    law of multiple proportionswhen two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers    
    main-group element(also, representative element) element in groups 1, 2, and 13–18    
    mass number (A)sum of the numbers of neutrons and protons in the nucleus of an atom    
    metalelement that is shiny, malleable, good conductor of heat and electricity    
    metalloidelement that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals    
    molecular compound(also, covalent compound) composed of molecules formed by atoms of two or more different elements    
    molecular formulaformula indicating the composition of a molecule of a compound and giving the actual number of atoms of each element in a molecule of the compound.    
    monatomic ionion composed of a single atom    
    neutronuncharged, subatomic particle located in the nucleus    
    noble gas(also, inert gas) element in group 18    
    nomenclaturesystem of rules for naming objects of interest    
    nonmetalelement that appears dull, poor conductor of heat and electricity    
    nucleusmassive, positively charged center of an atom made up of protons and neutrons    
    oxyacidcompound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)    
    oxyanionpolyatomic anion composed of a central atom bonded to oxygen atoms    
    period(also, series) horizontal row of the periodic table    
    periodic lawproperties of the elements are periodic function of their atomic numbers.    
    periodic tabletable of the elements that places elements with similar chemical properties close together    
    pnictogenelement in group 15    
    polyatomic ionion composed of more than one atom    
    protonpositively charged, subatomic particle located in the nucleus    
    representative element(also, main-group element) element in columns 1, 2, and 12–18    
    series(also, period) horizontal row of the period table    
    spatial isomerscompounds in which the relative orientations of the atoms in space differ    
    structural formulashows the atoms in a molecule and how they are connected    
    structural isomerone of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently    
    transition metalelement in groups 3–12 (more strictly defined, 3–11; see chapter on transition metals and coordination chemistry)    
    unified atomic mass unit (u)alternative unit equivalent to the atomic mass unit    

    2.9: Key Terms is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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