Chemistry 217

Unit 8
Basic Concepts of Chemical Bonding

Units 8 and 9 provide an overview of what we understand about chemical bonds. In chemistry, this is important stuff. It provides the basis for understanding chemical reactivity and molecular structure, which touch a large fraction of all scientific endeavours. For example, understanding the structures and reactivities of biomolecules is critical to explaining biochemistry, molecular biology, and physiology, all of which have applications in medicine. In geology, the chemical composition and structure of minerals is central to the discipline. Unit 8 is a survey of the basics of ionic and covalent bonding, including why chemical bonds have different bond energies, and how Lewis structures are drawn.

Objectives

After completing this unit, you should be able to

1. write the Lewis symbol for a Group A element.
2. define “lattice energy.”
3. construct the Born–Haber cycle for a given ionic compound.
4. calculate the lattice energy or the standard enthalpy of formation using a Born–Haber cycle and given appropriate data.
5. describe how the structure of ionic solids accounts for their stability.
6. write electron configurations for ions.
7. compare the characteristic properties of ionic and molecular substances.
8. explain the basis of the Lewis model for describing the bonding in molecular substances.
9. predict relative bond lengths for single, double, and triple bonds between the same pair of atoms.
10. define “electronegativity.”
11. describe the periodic trends in electronegativity.
12. predict the relative polarities of bonds using either the periodic table or a table of electronegativities.
13. use electronegativity differences to predict bond polarity and bond type.
14. draw Lewis structures for molecules and ions containing covalent bonds.
15. calculate formal charges for atoms in Lewis structures, and use formal charges to predict the most likely of a number of alternative Lewis structures.
16. write all the possible resonance forms for molecules or polyatomic ions not adequately described by a single Lewis structure.
17. identify the three types of exceptions to the octet rule, and write Lewis structures for molecules and ions of each type.
18. calculate ΔH for a reaction, given appropriate bond enthalpies.
19. estimate a bond enthalpy from a reaction enthalpy and other bond enthalpies.
20. relate bond enthalpies to strengths and lengths of covalent bonds.