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Answer Key: Review: Periodicity and Bonding


Go to the Review Sheet.

Periodicity Review

  1. Noble gases - last family on the periodic table; representative elements - s and p blocks; alkali metals - first family; alkaline earth metals - second family; halogens - family second from the end; transition metals - d-block elements; inner transition elements - f-block elements.
  2. See your text for the full explanation here. Be able to explain the trends. When time permits, I will write it out here.
  3. Cl-1. It has gained an electron and still has the same number of energy levels and protons, so the size is larger to allow space for the electron.
  4. Sr+2, Rb+1, Kr, Br-1, Se-2, As-3. They all have the same number of electrons, thus the same number of energy levels, but the protons differ. Sr has the most protons so it will pull the electrons in tighter than the others. The size increases as the number of protons decrease.
  5. As you go across the 3rd period the ionic sizes decreases until silicon. The ions of sodium through silicon all have the same number of electrons but silicon has more protons, which pulls the electrons in tighter. At phosphorus the ionic size increases dramatically, then decreases to chlorine. Phosphorus gains 3 e- and has fewer protons than sulfur which only gains 2 e- and chlorine which only gains 1 e-. Melting point increases as you go across, peaks at Si, then decreases to Ar.
    1. 2 Na   +   2 H2O   -->   2 NaOH   +   H2
    2. Cl2   +   2 Br-1   -->   2 Cl-1   +   Br2
    3. I2   +   Cl-1   -->   no reaction
    4. Br2   +   H2O   -->   HBr   +   HOBr
    5. 2 K   +   Br2   -->   2 KBr
    6. Ag+1   Br-1   -->   AgBr(s)
  6. As you go down the family the reactivity increases. Alkali metals want to lose electrons and as you go down a column the size increases making it easier for an electron to be removed, so therefore the reactivity increases.
  7. As you go down the halogen family the reactivity decreases. Halogens want to gain electrons and the smaller size at the top of the family allows electrons to be gained easier than the larger sizes.

Bonding Review

  1. a) 7   b) 4   c) 1   d) 6   e) 8   f) 8
  2. Answer to #2
  3. Answer for #4
  4. a) gain 1   b) gain 1   c) lose 2   d) gain 2
  5. To obtain a full outer shell and become like an inert gas.
  6. a) MgBr2   b) Al2S3   c) Li3P
  7. a) magnesium bromide b) aluminum sulfide c) lithium phosphide
  8. Ionic - complete transfer of electrons, covalent - sharing of electrons
  9. Polar - net partial charge, difference in electronegativity between the two elements. Nonpolar - very small difference in electronegativity, no partial charges. Both are covalent bonds.
  10. Answer to #11
  11. a) tetrahedral   b) pyramidal   c) bent   d) tetrahedral   e) linear   f) (square planar)   g) trigonal bipyramidal   h) trigonal planar   i) linear   j) octahedron
  12. a,b,e,i - polar the rest - nonpolar
  13. double - shorter bond length, more electrons shared
  14. Answer to #17
  15. Valence Shell Electron Pair Repulsion theory - all atoms (shared pairs) and unshared electrons want to spread out as much as possible.
  16. (O - F, Cl - O), Li - N, K - O
  17. a) ionic   b) covalent   c) ionic   d) ionic   e) covalent
  18. It is ionic between the Na+ and the PO4-3 ions. Covalent within the PO4-3 ion.
  19. Stronger dipole interactions which occur between molecules when H is bonded to either F, N, or O. This occurs because H is very electron deficient, having more of a partial positive charge than usual. The others have more of a partial negative charge.
  20. HCl is a dipole and the d+ on the H is attracted to Cl (with a d-) on a separate molecule. This attraction holds the molecules closer together to allow the substance to become a liquid.
  21. Dispersion forces or Induced dipoles. Dispersion forces are thought to be do to the motion of electrons. The more electrons present, the stronger the dispersion forces. Induced dipoles may also play a factor. An instantaneous dipole may form on one I2 molecule which can induce a dipole in another and have an instantaneous, weak attraction.
  22. It is ionic and the + and - ions are attracted to the d+ and d- on the water molecule.
  23. Yes. It is polar and will have dipole interactions with water to allow it to dissolve.
  24. No. It is nonpolar and will not be attracted to water. (Small amounts of nonpolar substances may dissolve due to induced dipoles, but not much.)
  25. For 24, use oil or another nonpolar liquid.
  26. Answer to #30
  27. The polar bonds pull evenly on the central atom, giving no net result.
  28. metallic
  29. network solid
  30. CH4 has the largest bond angles because all the electron pairs are shared. NH3 is smaller because the unshared pair of electrons repel the shared pairs (hydrogen atoms) more than a shared pair, pushing the hydrogens closer together. H2O has the smallest bond angle because it has two unshared pairs of electrons which repel each other even more, pushing the hydrogens even closer together.
  31. C2H2, C2H4, C2H6. Triple bonds are the shortest, single bonds the longest.
  32. Forming 3 C-Cl bonds, 1 C-H bond. Enthalpy = 3(339) + 1(413) = 1430 kJ.
  33. CH4 (g)   +   2 Cl2 (g)   +   2 F2 (g)   -->   CF2Cl2 (g)   +   2 HF (g)   +   2 HCl (g)
    DHrxn = Energy needed to break bonds - Energy needed to form bonds.
    Bonds to break: 4(C-H), 2(Cl-Cl), 2(F-F)
    Bonds to form: 2(C-F), 2(C-Cl), 2(H-F), 2(H-Cl)
    DHrxn = [4(413) + 2(239) + 2(154)] - [2(485) + 2(339) + 2(565) + 2(427)] = -1194 kJ



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