Covalent Bonds Page 87 Essential question: How does the formation of covalent bonds differ from the formation of Ionic bonds?

Types of Bonding  Covalent Results from the sharing of electron pairs between two atoms  Ionic Results from the electrical attraction between cations and anions

Different Covalent Bonds Nonpolar-covalent Bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge (EN = ) Polar-covalent Polar-covalent Bonded atoms have an unequal attraction for the shared electrons (EN = 0.4 – 1.7)

Molecule A NEUTRAL group of atoms that are held together by covalent bonds Diatomic molecules: molecules containing only 2 atoms

Chemical Compound Terms  Chemical Formula Indicates the relative #’s of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts  Molecular Compound A chemical compound whose simplest units are molecules  Molecular Formula Shows the types and numbers of atoms combined in a single molecule of a molecular compound

Formation of a Covalent Bond

Characteristics of a Covalent Bond PE remains close to minimum regardless of small vibrations of the bonded atoms Bond length: The distance between two bonded atoms at their minimum PE (average distance between bonded atoms) Bond energy: The energy required to break a chemical bond and form neutral isolated atoms Happens between nonmetals (nonmetallic)

The Octet Rule Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level Octet = 8 = s 2 + p 6

Exceptions to the Octet Hydrogen  2 electrons Boron  tends to form with 6 electrons because of its 3 valence e - Sometimes bonding occurs with d orbitals which contain more than 8 e - as stated in the octet rule Boron trifluoride BF 3