Chapter 9 and 10 Review

10.6. How do you apply VSEPR theory to predict the shape of a molecule with more than one interior atom?

Larger molecules may have two or more interior atoms. When predicting the shapes of these molecules, determine the geometry about each interior atom and use these geometries to determine the entire three-dimensional shape of the molecules.

9. What is lattice energy?

Lattice energy is associated with forming a crystalline lattice of alternating cations and anions from the gaseous ions. Because the cations are positively charged and the anions are negatively charged, there is a lowering of potential—as described by Coulomb's law—when the ions come together to form a lattice. That energy is emitted as heat when the lattice forms.

10.2. According to VSEPR theory, what determines the geometry of a molecule?

According to VSEPR theory, the repulsion between electron groups on interior atoms of a molecule determines the geometry of the molecule.

1. Why are bonding theories important? Provide some examples of what bonding theories can predict.

Bonding theories are central to chemistry because they explain how atoms bond together to form molecules. Bonding theories explain why some combinations of atoms are stable and others are not.

5. Describe the octet rule in the Lewis model

Bonds are formed when atoms attain a stable electron configuration. Because the stable configuration usually has eight electrons in the outermost shell, this is known as the octet rule.

2. Why do chemical bonds form? What basic forces are involved in bonding?

Chemical bonds form because they lower the potential energy between the charged particles that compose the atom. Bonds involve the attraction and repulsion of charged particles.

30. What elements can have expanded octets? What elements should never have expanded octets?

Elements in the third row of the periodic table and beyond often exhibit expanded octets. Elements in the first or second row of the periodic table never have expanded octets.

6. According to the Lewis model, what is a chemical bond?

In Lewis theory, a chemical bond is the sharing or transferring of electrons to attain stable electron configurations for the bonding atoms. If electrons are transferred, the bond is an ionic bond. If the electrons are shared, the bond is a covalent bond.

4. How do you determine how many dots to put around the Lewis symbol of an element?

In a Lewis structure, the valence electrons of main-group elements are represented as dots surrounding the symbol for the element. The valence electrons can be determined from the group they are in on the periodic table.

3. What the three basic types of chemical bonds? What happens to electrons in the bonding atoms in each type?

The three types of bonds are ionic bonds, which occur between metals and nonmetals and are characterized by the transfer of electrons; covalent bonds, which occur between nonmetals and are characterized by the sharing of electons; and metallic bonds, which occur between metals and are characterized by electrons being pooled.

33. What is the electron sea model for bonding in metals?

When metal atoms bond together to form a solid, each metal atom donates one or more electrons to an electron sea.

12. How does lattice energy relate to ionic radii? To ion charge?

a. As the ionic radii increase as you move down a group, the ions cannot get as close to each other and therefore do not release as much energy when the lattice forms. Thus, the lattice energy decreases (becomes less negative) as the radius increases. b. Because the magnitude of the potential energy of two interacting charges depends not only on the distance between the charges but also on the product of the charges, the lattice energies become more exothermic with increasing magnitude of ionic charge.

20. Explain the difference between a pure covalent bond, a polar covalent bond, and an ionic bond.

a. If two elements with identical electronegativities form a covalent bond, they share the electrons equally, and the bond is purely covalent or non polar. b. If there is an intermediate electronegativity difference between the two elements, such as between two different non-metals, the bond is polar covalent. c. If there is a large electronegativity difference between the two elements in a bond, such as normally occurs between a metal and a nonmetal, the electron from the metal is almost completely transferred to the nonmetal, and the bond is ionic.

10.4. Explain the difference between electron geometry and molecular geometry. Under what circumstances are they not the same?

a. The electron geometry is the geometrical arrangement of the electron groups around the central atom. b. The molecular geometry is the geometrical arrangement of the atoms around the central atom. c. The electron geometry and the molecular geometry are the same when every electron group bonds two atoms together. The presence of unbounded lone pair electrons gives a different molecular geometry and electron geometry.

10.3. Name and sketch the five basic electron geometries, and state the number of electron groups corresponding to each. What constitutes an electron group?

a. The five basic electron geometries are as follows: i. Linear, which has two electron groups ii. Trigonal planar, which has three electron groups iii. Tetrahedral, which has four electron groups iv. Trigonal bipyramidal, which has five electron groups v. Octahedral, which has six electron groups

25. How do you determine the number of electrons that go into the Lewis structure of a molecule? A polyatomic ion?

a. The total number of electrons for a Lewis structure of a molecule is the sum of the valence electrons of each atom in the molecule. b. The total number of electrons for the Lewis structure of an ion is found by summing the number of valence electrons for each atom and then subtracting one electron for each positive charge or adding one electron for each negative charge.

10.7. How do you determine if a molecule is polar? Why is polarity important?

a. To determine whether a molecule is polar, do the following: i. Draw the Lewis structure for the molecule and determine the molecular geometry. ii. Determine whether the molecule contains polar bonds. iii. Determine whether the polar bonds add together to form a net dipole moment. b. Polarity is important because polar and nonpolar molecules have different properties. Polar molecules interact strongly with other polar molecules but do not interact with nonpolar molecules, and vice verse.

10. Why is the formation of solid chloride from solid sodium and gaseous chlorine exothermic, even though it takes more energy to form the Na+ ion than the amount of energy released upon formation of Cl-?

the formation of ionic compounds is not exothermic because sodium "wants" to lose electrons and chlorine "wants" to gain them; rather, it is exothermic because of the large amount of heat released when sodium and chlorine ions coalesce to form a crystal lattice.