1) B – Quartz is the only covalent network solid present 2) C – all are molecular, except Al, which is a metal 3) C – Neon is an atomic solid, held together only by London dispersion forces 4) C – Cl2 is a nonpolar molecular compound, like I2, but has a lower MP because it is a lower molecular weight, which influences London dispersion forces. 5) D – H is not bonded to N, O, or F 6) D – Silicon is the only covalent network solid present 7) D – Argon is an atomic solid, held together only by London dispersion forces 8) C – Br2 is a nonpolar molecular compound, like I2, but has a lower MP because it is a lower molecular weight, which influences London dispersion forces 9) B – SO2: Lewis structure is bent 10) E – Melting an ionic compounds means breaking ionic bonds, which are more energetic than breaking the IMFs in the other options. 11) E – CaO has the ionic charges of greatest magnitude, and the smallest ionic radii.

12) A – metallic bonds B – ionic bonds C – H-bonds D – H-bonds 13) A – True (ionic bonds are stronger than dipole-dipole) B – True (H-bonds are stronger than dipole-dipole) C – False (It sublimes.) D – False (I2 has greater mass, so greater London-dispersion forces) 14) A – Neon has lower mass, so weaker London dispersion forces) B – Electrons are localized in ionic solids, but delocalized in metallic solids C – Group IV has a nonmetal (C), metalloids (Si, Ge), and metals (Sn, Pb). Therefore, there are many types of bond that they make in different substances. D – BF3 is nonpolar, trigonal planar molecule since B is stable with an incomplete octet, while PF3 is a polar, trigonal bipyramidal molecule. 15) A – Larger metallic atoms means weaker metallic bonds since valence electrons are held more loosely. B – Increasing mass means greater London dispersion forces. C – BP decreases - as ions get larger, ionic forces of attraction (lattice energy) decreases

16 (A). Butane is nonpolar; chloroethane is polar 16 (A) Butane is nonpolar; chloroethane is polar. Intermolecular forces of attraction in liquid chloroethane are larger due to dipole-dipole attraction; thus a higher boiling point for chloroethane. (B) Both chloroethane and acetone are polar. Although acetone molecules cannot hydrogen bond with each other, acetone has lone pairs electrons on its oxygen for water to hydrogen bond to resulting in greater solubility of acetone in water. (C) Butane is non-polar and cannot form hydrogen bonds; 1-propanol is polar and can form hydrogen bonds. 1-propanol can interact with water by both dipole-dipole forces and hydrogen bonds. Butane can interact with water by neither means. Thus, 1-propanol is much more soluble. (D) Acetone molecules are attracted to each other by van der Waals attraction and dipole-dipole attraction. 1-propanol molecules show these two types of attraction. However, 1-propanol molecules can also undergo hydrogen bonding with one another. This distinguishing feature results in the higher boiling point of 1-propanol.

17 (A) H2 and C3H8 have low melting points because the only IMF’s involved are the London forces. HF has a higher melting point because intermolecular hydrogen bonding is involved in holding the molecules together. CsI and LiF have still higher melting points because ionic lattice forces must be overcome to break up the crystals, and the ionic forces are stronger than van der Waals forces (IMF’s) SiC is an example of a macromolecular substance where each atom is held to its neighbors by very strong covalent bonds (covalent network solid). (B) C3H8 and H2: the only IMF’s involved are the London forces which increase in strength with increasing mass. LiF and CsI: The smaller ions in LiF result in a higher lattice energy than CsI has. Stronger lattice energy is proportional to higher melting point.

18.  Xe and Ne are monatomic elements held together by London dispersion forces. The magnitude of such forces is determined by the number of protons in the species. A Xe atom has more protons than a neon atom has. (B) The electrical conductivity of copper metal is based on mobile valence electrons (delocalized electrons in the d-orbital). Solid copper (II) chloride is a rigid ionic solid with the valence electrons of copper localized in individual copper(II) ions. Copper (II) chloride solution is a solution containing individual Cu2+ and Cl- ions. (C) SiO2 is a covalent network solid. There are strong bonds, many of which must be broken simultaneously to melt SiO2. CO2 is composed of discrete, nonpolar CO2 molecules so that the only forces holding the molecules together are weak van der Waals forces. (D) In NF3 a lone pair of electrons on the central atom results in a trigonal pyramidal shape. The dipoles don’t cancel, thus the molecule is polar. While in BF3 there is no lone pair on the central atom so the molecule has a trigonal planar shape in which the dipoles cancel, thus the molecule is nonpolar.  

___ ___ ___ ___ ___ ___ ___ ___ ___ 1s 2s 2p 3s 3p   19. B) Nuclear charge goes from +11 to +17; accordingly electrons are attracted more to the nucleus . . . . . electron affinity, thus electronegativity is greater but atomic radius is smaller. 20. A) As we move down a group, the atoms get larger as outer shells are filling up. 21. A) removing an electron from oxygen involves overcoming the attractive force of 8 protons whereas removing an electron from neon involves overcoming the attractive force of 10 protons 22. B) it is easier to remove an electron from a shell further from the nucleus; removing an electron from sodium involves overcoming the attractive force of 11 protons whereas removing an electron from aluminum involves overcoming the attractive force of 13 protons 24) (A) isotopes of a given element simply have different numbers of neutrons. Selenium atoms always have 34 protons, however each of the six isotopes will have a different number of neutrons. (B) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 . . . . . There are two unpaired electrons in the 4p-orbital (C) accordingly, selenium is paramagnetic   ___ ___ ___ ___ ___ ___ ___ ___ ___ 1s 2s 2p 3s 3p ___ ___ ___ ___ ___ ___ ___ ___ ___ 4s 3d 4p

thus it is harder to remove (i) an outer electron in Br is held by one more proton than an outer electron in Se and thus it is harder to remove (ii) an outer electron in Te is held further from the nucleus than an outer electron in Br, so, even though Te has more protons in its nucleus than Br, shielding from the inner electrons makes the effective nuclear charge of Te smaller and thus the electron easier to remove. (E) Molecule is polar as the lone pair make it asymmetrical so the dipoles don’t cancel (F) SeF4 is in the trigonal bipyramidal domain (4 bonds and one lone pair) – thus Se must undergo sp3d hybridization. Oxygen doesn't have a d orbital to undergo this hybridization. (D) The central atom in SeF2 and OF2 are in the tetrahedral domain in the (2 bonds and two lone pairs) – thus the central atom undergoes sp3 hybridization, which is possible for both of them.

24.   The outer electrons in a Ca atom are in the 4s orbital whereas the outer electrons in a Ca2+ ion are in the 3p orbital . . . . closer to the nucleus. (B) (i) The first ionization energy for Ca and K are similar because the electron being removed is in the valence shell (4s) . . . . The value for potassium is smaller because there is one less proton attracting the electron being removed. (ii) The second ionization energies are vastly different because the electron under consideration for K is in an inner shell whereas the electron under consideration for Ca is still a valence electron. (C) The first ionization energy for Mg and Al are similar because the electron being removed is in the valence shell, but for Mg it is in the 3s orbital and for Al it is in the 3p orbital. . . . . The value for magnesium is larger because the electron being removed is from the 3s orbital which requires more energy to remove than the electron being removed from the 3p orbital in aluminum.