6.2 Covalent Bonding

Key Concepts How are atoms held together in a covalent bond? What happens when atoms don’t share electrons equally? What factors determine whether a molecule is polar? How do attractions between polar molecules compare to attractions between nonpolar molecules?

Vocabulary Covalent bond Molecule Polar covalent bond

Covalent Bonds When dealing with nonmetals, electrons typically don’t transfer Consider: a treasure hunt with a prize Instead, nonmetal atoms tend to share their electrons to achieve stable electron configurations A chemical bond in which two atoms share a pair of valence electrons is a covalent bond Atoms can share more than one pair of electrons

Molecules of Elements A molecule is a group of atoms that are joined together by one or more covalent bonds The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond. Chemical formulas can be used to describe the molecules of an element as well as a compound. Many nonmetal elements exist as diatomic molecules. There are many different ways to represent covalent bonds.

Electron Dot and Structural Formula http://www.wikinfo.org/upload/5/5d/Electron_dot.jpg

Space Filling / Electron Cloud Models

Unequal Sharing of Electrons Generally trends on the periodic table: elements towards the right of the periodic table tend to have greater attractions for electrons than elements on the left elements at the top of a group have a greater attraction for electrons than elements at the bottom of a group These trends typically cause covalently bonded atoms to share electrons unequally

Polar Covalent Bonds In molecules of elements, both atoms attract electrons equally In compounds, this isn’t necessarily the case A covalent bond in which electrons are not shared equally is called a polar covalent bond Example: Water When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge. This is represented by either δ+ or δ-

Polar and Nonpolar Molecules If a molecule has only two atoms, it will be polar When atoms have more than two atoms, they might not be polar The type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar. Compare: Carbon Dioxide and Water

Comparing CO2 and H2O Carbon Dioxide Water

Attraction Between Molecules In a molecular compound, there are forces of attraction between molecules These attractions are not as strong as ionic or covalent bonds, but strong enough to hold together molecules in a liquid or solid Attractions between polar molecules are stronger than attractions between nonpolar molecules Example: Water

Exit Ticket What attractions hold atoms together in a covalent bond? What happens to the charge on atoms when they form a polar covalent bond? Name the two factors that determine whether a molecule is polar. Compare the strength of attraction between polar molecules to the strength of attraction between nonpolar molecules.