Chemical Naming and Structure: Review

Review

• Ionic bonding occurs between a metal atom and a nonmetal atom, due to their large difference in electronegativity.
• Covalent bonding occurs between two identical nonmetal atoms, due to their identical electronegativities.
• Ionic compounds are held together by strong ionic bonds, while molecular compounds are held together by much weaker intermolecular attractions—either van der Waals attractions or hydrogen bonds.
  • Substances with weaker attractions vaporize more easily, giving rise to higher vapor pressure.
  • Substances with weaker attractions can be moved out of position more easily, leading to a lower melting point.
  • Substances with weaker attractions can be separated from each other more easily, therefore having lower boiling points.
• Polar covalent bonding occurs between two different nonmetal atoms, due to their moderately different electronegativities.
• Nonmetals bond with each other covalently to form discrete particles called molecules.
• Metal atoms bond with each other through a “sea of electrons”—electrons that freely float between metal atoms that are patterned in a three-dimensional network.
• The arrangement of electrons and atoms in a molecule can be shown with a Lewis structure.
• Most Lewis structures may be drawn by counting available valence electrons and distributing them around the molecule according to the Octet Rule.
• Resonance structures are necessary when more than one valid Lewis structure may be drawn for the same molecule.
• Nonmetals from the third period or beyond may have more than eight electrons in a valid Lewis structure.
• Because pairs of valence electrons are negatively charged, they will repel each other and move as far apart as possible. This allows us to predict the shape of a molecule from its Lewis structure.
• In VSEPR, single, double and triple bonds all behave as only one region of electron density.
• Molecules with central atoms that obey the Octet Rule may have shapes that are linear, trigonal planar, tetrahedral, trigonal pyramidal, or bent.
• Molecules with central atoms that have more than eight valence electrons may have shapes that are trigonal bipyramidal, see-saw, T-shaped, linear, octahedral, square pyramidal, or square planar.
• If a molecule has more than one central atom, we only consider one central atom at a time.
• Different types of hybrid orbitals correspond to the number of regions of electron density and the shapes predicted by VSEPR.
  • Two regions = sp hybridization = linear
  • Three regions = sp² hybridization = trigonal planar
  • Four regions = sp³ hybridization = tetrahedral
  • Five regions = dsp³ hybridization = trigonal bipyramidal
  • Six regions = d²sp³ hybridization = octahedral
• Molecular compounds are named with prefixes, such as “mono-,” “di-“, etc.
• Ionic compounds are named by naming the positive ion followed by the name of the negative ion.
• Monatomic negative ions end with “-ide,” while polyatomic negative ions usually end with “-ite” or “-ate.”
• An ionic formula is the lowest whole number ratio of ions whose charges add up to zero.
• If there is more than one polyatomic ion in a formula, its formula must be in parentheses with the subscript outside.
• Acids are formed from the combination of hydrogen ion(s) and an anion.
• The name of the acid is dependent upon the name of the anion.
• Acid names are generated from the anion name as follows:
  • For ions that end with “-ide,” place “hydro” in front of the anion name and replace “-ide” with “-ic acid.”
  • For ions that end with “-ite,” replace “-ite” with “-ous acid.”
  • For ions that end with “-ate,” replace “-ate” with “-ic acid.”
• Oxidation numbers may be used in situations where true charges may not apply.
• Oxidation numbers may be assigned using the following rules:
  • Elements are zero.
  • Hydrogen and oxygen in compounds are +1 and −2, respectively.
  • Monatomic ions are equal to their charges.
  • Others are assigned so that the sum equals the charge on the species.
• Metal oxides react with water to form metal hydroxides, which are basic.
• Nonmetal oxides react with water to form oxyacids.
• When nonmetal oxides react with water, the oxidation number of the nonmetal does not change.
• Percent composition is calculated by dividing the mass of each element by the total mass of the compound, and then multiplying by 100%.
• The empirical formula is found by converting mass data into moles and reducing the ratio to the lowest whole number.
• The molecular formula is found by dividing the molar mass by the mass of the empirical formula to get a whole number, and then multiplying the empirical formula by this whole number.

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