Most elements found in nature are in a combined form, meaning they are most likely to exist as a molecule or compound. In Chapters 6 and 7 we discussed how the electrons are arranged in atoms and in Chapters 8 and 9 we will analyze how these electrons are either shared or transferred to form chemical bonds.
8.1 Chemical Bonding Overview
In Chapter 6 we placed heavy emphasis on valence electrons, as these electrons are the ones involved in bonding. Lewis Theory places emphasis on the valence electrons and drawing Lewis Symbols provides a convenient way to represent them. Lewis Theory also introduces us to the octet rule.
8.1 Lewis Theory
Ionic bonding results from the transfer of electrons in order to achieve a noble gas electron configuration, or octet. Typically, ionic bonding occurs between a metal and a nonmetal.
8.2 Ionic Bonding
Covalent bonding results from the sharing of electrons in order for two or more atoms to collectively achieve a noble gas configuration, or octet. Typically, covalent bonding occurs between a nonmetal and a nonmetal.
8.3 Covalent Bonding
Covalent bonding is described as the sharing of electrons, but when two or more atoms share their electrons to form a bond, often times the electrons are not shared evenly. This uneven sharing of electrons creates a partial positive and partial negative end of the molecule, or we can say that molecules resulting from the uneven sharing of electrons are polar. Note: The electronegativity video introduced from last chapter is also shown below.
8.4 Bond Polarity and Electronegativity
It would be convenient to simply characterize a bond as either ionic or covalent, but in reality there is a continuum of bonding and it is fairly difficult to place black and white boundaries on the types of bonding we will observe.
8.4 Ionic vs. Covalent Bonding
A dipole moment, which results from an uneven sharing of electrons, can be described by looking at how the electrons orbit the nucleus. The electronegativity difference between atoms allow us to predict how strong a dipole moment will be.
8.4 Dipole Moments
Drawing and interpreting Lewis Structures provides a convenient way of to represent how atoms bond together to form molecules. A generic method for drawing Lewis Structures along with a few examples are shown in the following videos.
8.5 Drawing Lewis Structures Part 1
8.5 Drawing Lewis Structures Part 2
8.5 Examples of Lewis Structures
*Note: Formal Charges, Resonance Structures, and Exceptions to the Octet Rule will be covered after we discuss Molecular Shapes and VSEPR Theory in Chapter 9.
The stronger a bond the more stable it is. If a molecule consists of extremely stable bonds then it will be more stable than a molecule consisting of weak bond. We discussed stability in Chapter 5 and we can relate bond strength to the enthalpy change of a chemical reaction by comparing the bonds broken in the reactants to the bonds formed in the products.
8.8 Estimating Enthalpy Using Bond Enthalpies