LITMIR.BIZ

       Ionic and covalent bonds, common in ceramics, and metallic bonding, common in metals and metal alloys, are the three types of primary bonds. Polymers have strong interatomic covalent bonds between atoms in the chain backbone but weak intermolecular bonding between the chains.

       We discussed representations of the interaction between two atoms, in terms of a force or potential energy as a function of interatomic distance, which provide a useful way to understand how many of the intrinsic properties of a material arise

       Van der Waals and hydrogen bonds are the main types of intermolecular bonding

       Proteins, the most versatile macromolecules in living organisms, have a complex three‐dimensional shape (conformation) that is determined by intrachain and interchain covalent and noncovalent bonds. We discussed how the bonding in proteins determines their overall three‐dimensional shape, which, in turn, has a critical effect on their functionality.

      1 2.1 Predict the type of bond (ionic, covalent, metallic, or a combination of these) that will be present in each of the following molecules. Explain your answer.NaFCH4Al2O3SiCCHCl3

      2 2.2 Distinguish between intrinsic properties of materials and their engineering properties, indicating how these properties are dependent on the structure of a material.

      3 2.3 Given the ionic radii of the following ions: sodium = 0.102 nm; chlorine = 0.181 nm; magnesium = 0.072 nm; oxygen = 0.140 nm, determine the potential energy of attraction in (kJ/mol) for (i) the NaCl molecule, and (ii) the MgO molecule at a separation distance equal to the sum of the ionic radii. Comment on the difference between these values and the bonding energy in Table 2.2 for these molecules.

      4 2.4 Sodium chloride (NaCl) and silicon dioxide (SiO2) are respectively among the prototype ionic and covalent solids. The electronegativities of the atoms in the Pauling electronegativity scale are as follows: sodium = 0.93; chlorine = 3.16; silicon = 1.90; oxygen = 3.44. Determine the percentage ionic and covalent character of the bonds in NaCl and SiO2 according to Eq. (2.5).

      5 2.5 Carbon and silicon both have four electrons in their outermost shell but carbon dioxide is a gas at room temperature whereas silicon dioxide is a solid with a high melting point. Explain.

      6 2.6 Explain why hydrogen fluoride (HF) has a higher boiling point (19.4 °C) than that (−85 °C) of hydrogen chloride (HCl) even though its molecular weight is lower.

      7 2.7 The trichloromethane (CHCl3) molecule is polar whereas the tetrachloromethane molecule is nonpolar but, despite its polarity, trichloromethane has a boiling point (61.2 °C) that is lower than that of tetrachloromethane (76.7 °C). Explain.

      8 2.8 The pKa values of the side groups in the amino acids glutamic acid, arginine and histidine are 4.3, 12.5, and 6.0, respectively. With the aid of a sketch of each amino acid residue, explain whether the side group will have a positive or negative charge at the physiological pH, and indicate the position of the charge on the side group.

      1 Alberts, B., Johnson, A.D., Lewis, J. et al. (2014). Molecular Biology of the Cell, 6e. New York: W W Norton & Company Chapter 3.

      1 Callister, W.D. (2007). Materials Science and Engineering: An Introduction, 7e. New York: Wiley Chapter 2.

      2 Ebbing, D.D., Gammon, S.D., and Ragsdale, R.O. (2006). Essentials of General Chemistry, 2e. Boston, MA: Houghton Mifflin Company Chapter 9.

      3 Shoulders, M.D. and Raines, R.T. (2009). Collagen structure and stability. Annual Review of Biochemistry 78: 929–958.