13.1 CO2 has a linear shape and therefore has no dipole moment and no charge. It has two C=O double bonds. SO2 has a bent shape with a lone pair of electrons on the S, and has a charge and a dipole moment. It has a single S-O bond and a double S=O bond.
13.2 H3O and NH3 both have a tetrahedral shape and therefore have polarity. Both have three hydrogen atoms, and at the apex of the tetrahedron, ammonia has a nitrogen atom and the hydronium ion has an oxygen atom. Their shapes and polarities are the same for both compounds. They are isoelectronic because they both have the same number of valence electrons and the same Lewis dot structures.
13.3 The Lewis dot structure represents the valence electrons for the various elements in a compound (Lewis, 2004). Lewis dot structures are used to describe the chemical bonding in molecules or ions. In the formation of chemical bonds completes the octet of electrons for each atom. If several dot structures are possible for a molecule or ion, they all contribute to the molecular or ionic structure, making it more stable. The representation of a molecular or ionic structure by several structures is known as resonance, and the more stable the dot structure is, the more it contributes to the electronic structure of the molecule or ion. When drawing the Lewis dot structure for an ion, it is necessary to add or subtract electrons corresponding to the charge on the ion, i.e. add electrons for every negative charge and subtract electrons for every positive charge. The octet rule cannot be satisfied for all compounds.
Dissociation reactions: Ammonia NH4 ? NH3 + H+
Vinegar CH3COOH ? CH3COO- + H+
14.2a Many substances change color in response to the presence of an acid or an alkali: these are known as acid-base indicators (Dice, 1998). Examples of commonly used indicators are litmu
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