Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 77

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.