Chapter 6: Chemical Bonding Section 2: Covalent Bonding and Molecular Compounds

Overview We will define molecule and molecular formula. We will explain the relationships between potential energy, distance between approaching atoms, bond length, and bond energy. We will state the octet rule. We will see how to write Lewis structures. We will explain why people use resonance structures.

Molecule A neutral group of atoms that are held together by covalent bonds. Molecular Compound – A chemical compound whose simplest units are molecules. Chemical Formula – It indicates the number of atoms by using atomic symbols and subscripts. Molecular Formula – Shows the types and numbers of atoms in a single molecule. Diatomic Molecule – A molecule that has only two atoms.

Forming Covalent Bonds Approaching electrons are attracted so there is a decrease in potential energy. The nuclei also repel each other which increases potential energy. See page 165, Figure 6-5

Covalent Bond Characteristics Bond Length – The distance between two bonded atoms at their minimum potential energy. AKA average distance between two bonded atoms. Bond Energy – The energy required to break a chemical bond or form neutral isolated atoms.

Octet Rule Chemical compounds tend to form so that each atom has an octet of electrons in its highest energy level by gaining, losing, or sharing electrons. Exceptions: Hydrogen and Helium only need two valence electrons. Boron can have less than eight, others can have more than eight.

Electron-Dot & Lewis Structures Electron Dot Notation – An atom’s atomic symbol with only dots representing the valence electrons. An unshared pair or lone pair is two electrons that are not involved bonding. Lewis Structure – The electron dot notation of a molecule showing bonds.

More Lewis Structures Structural Formula – It indicates the kind, number, arrangement, and bond types, but not the unshared pairs. Single Bond – A covalent bond with two electrons being shared. (Single Line) Double Bond – A covalent bond with four electrons being shared. (Two Lines) Triple Bond – A covalent bond with six electrons being shared. (Three Lines) Multiple Bonds – A double or triple bond.

Resonance The bonding of molecules that cannot be represented correctly by just one Lewis Structure. There is more than one way to assemble the same number of elements the right way.

How do you make these?