How do atoms make compounds? Typically they join together in such a way that they lose their identities as elements and adopt a new identity as a compound. These joins are called chemical bonds . But how do atoms join together? Ultimately, it all comes down to electrons. Before we discuss how electrons interact, we need to introduce a tool to simply illustrate electrons in an atom. 12.01 Lewis Electron Dot Diagrams Lewis electron dot diagrams use dots to represent valence electrons around an atomic symbol. Lewis electron dot diagrams for ions have less (for cations) or more (for anions) dots than the corresponding atom. 12.02: Ionic and Covalent Bonds There are many types of chemical bonds and forces that bind molecules together. The two most basic types of bonds are characterized as either ionic or covalent. In ionic bonding, atoms transfer electrons to each other. Ionic bonds require at least one electron donor and one electron acceptor. In contrast, atoms with the same electronegativity share electrons in covalent bonds, because neither atom preferentially attracts or repels the shared electrons. 12.03: Bond Polarity 12.04: Electron Transfer - Ionic Bonds The tendency to form species that have eight electrons in the valence shell is called the octet rule. The attraction of oppositely charged ions caused by electron transfer is called an ionic bond. The strength of ionic bonding depends on the magnitude of the charges and the sizes of the ions. 12.05: Covalent Bonds Covalent bonds are formed when atoms share electrons. Lewis electron dot diagrams can be drawn to illustrate covalent bond formation. Double bonds or triple bonds between atoms may be necessary to properly illustrate the bonding in some molecules. 12.06: Lewis Structures 12.07: Violations of the Octet Rule There are three violations to the octet rule: odd-electron molecules, electron-deficient molecules, and expanded valence shell molecules. 12.08: Molecular Shapes The approximate shape of a molecule can be predicted from the number of electron groups and the number of surrounding atoms. 12.09: Polar Molecules