Chapter 2
Atoms, Molecules, and Ions
By Boundless
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The concept of the atom as an indivisible building block of matter was recorded as early as the 5th century BCE.
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The law of conservation of mass states that mass in an isolated system is neither created nor destroyed.
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The law of definite composition states that chemical compounds are composed of a fixed ratio of elements as determined by mass.
The law of multiple proportions states that elements combine in small whole number ratios to form compounds.
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Dalton introduced a theory that proposed that elements differed due to the mass of their atoms.
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Atoms are made up of particles called protons, neutrons, and electrons, which are responsible for the mass and charge of atoms.
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The atomic number is the number of protons in an element, while the mass number is the number of protons plus the number of neutrons.
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Isotopes are various forms of an element that have the same number of protons, but a different number of neutrons.
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The periodic table shows all the elements and their physical properties; it is arranged based on atomic numbers and electron configurations.
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Molecules are electrically neutral compounds made of multiple atoms bound together by chemical bonds.
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An ion is an atom or molecule that has a net electrical charge because its total number of electrons is not equal to its number of protons.
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Chemical bonding describes a variety of interactions that hold atoms together in chemical compounds.
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Ionic bonds are a subset of chemical bonds that result from the transfer of valence electrons, typically between a metal and a nonmetal.
Covalent bonding involves two atoms, typically nonmetals, sharing valence electrons.
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Molecular formulas are a compact chemical notation that describe the type and number of atoms in a single molecule of a compound.
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Empirical formulas describe the simplest whole-number ratio of the elements in a compound.
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An ionic formula must satisfy the octet rule for the constituent atoms and electric neutrality for the whole compound.
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An ionic compound is named first by its cation and then by its anion.
Molecular compounds are named using a systematic approach of prefixes to indicate the number of each element present in the compound.
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Acid names are based on the anion they form when dissolved in water; base names follow the rules for ionic, organic, or molecular compounds.
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The name of a hydrate follows a set pattern: the name of the ionic compound followed by a numerical prefix and the suffix -hydrate.
Familiar inorganic and organic compounds are often known by their common, or "trivial," names.