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alpha particle (α particle)
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positively charged particle consisting of two protons and two neutrons
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anion
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negatively charged atom or molecule (contains more electrons than protons)
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atomic mass
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average mass of atoms of an element, expressed in amu
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atomic mass unit (amu)
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(also, unified atomic mass unit, u, or Dalton, Da) unit of mass equal to
of the mass of a
12
C atom
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atomic number (Z)
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number of protons in the nucleus of an atom
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cation
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positively charged atom or molecule (contains fewer electrons than protons)
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chemical symbol
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one-, two-, or three-letter abbreviation used to represent an element or its atoms
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Dalton (Da)
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alternative unit equivalent to the atomic mass unit
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Dalton’s atomic theory
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set of postulates that established the fundamental properties of atoms
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electron
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negatively charged, subatomic particle of relatively low mass located outside the nucleus
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empirical formula
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formula showing the composition of a compound given as the simplest whole-number ratio of atoms
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fundamental unit of charge
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(also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602
10
−19
C
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ion
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electrically charged atom or molecule (contains unequal numbers of protons and electrons)
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isomers
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compounds with the same chemical formula but different structures
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isotopes
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atoms that contain the same number of protons but different numbers of neutrons
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law of constant composition
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(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
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law of definite proportions
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(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass
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law of multiple proportions
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when 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
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mass number (A)
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sum of the numbers of neutrons and protons in the nucleus of an atom
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molecular formula
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formula 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.
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neutron
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uncharged, subatomic particle located in the nucleus
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nucleus
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massive, positively charged center of an atom made up of protons and neutrons
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proton
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positively charged, subatomic particle located in the nucleus
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spatial isomers
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compounds in which the relative orientations of the atoms in space differ
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structural formula
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shows the atoms in a molecule and how they are connected
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structural isomer
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one of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently
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unified atomic mass unit (u)
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alternative unit equivalent to the atomic mass unit