Molecular Bonding and Nomenclature

Molecular Bonding Binary molecular compounds form between 2 non-metals Covalent bonds: shared electrons Each atom counts the electrons as part of their octet Molecular formula: shows number and kind of atoms in a molecule

Molecular Naming Use a prefix to identify the number of atoms present in the molecule 1: mono 2: di 3: tri 4: tetra 5: penta 6: hexa 7: hepta 8: octa 9: nona 10: deca Second element in name ends with –ide If only one of the first element do not need mono-

Questions How does molecular bonding differ from ionic bonding? Why must a prefix be used to distinguish between CO and CO2?

Writing Molecular Formulas Use prefix to determine the number of atoms Write the subscript behind the atom in the formula to show the number of atoms

Covalent Bonds Single Covalent Bonds: 2 atoms share a pair of electrons so that each achieves an octet F2 NH3

Covalent Bonds Double Covalent bond: 2 atoms share 2 pairs of electrons O2 Triple Covalent Bond: 2 atoms share 3 pairs of electrons N2

Structural Formula Shows the arrangement of atoms in a molecule or a polyatomic ion The pair of shared electrons is represented as a dash H2 H-H Practice: NH3 F2 N2

Exceptions to the Octet Rule BF3 Boron is stable with 6 electrons in its valence shell P and S sometimes expand their octet to include 10 or 12 electrons. PCl3, PCl5, SF6

Polar Covalent Bonds Sometimes electrons are not shared equally in a covalent bond Atom with higher electronegativity draws electrons toward itself, pulling those electrons away from the atom of lower electronegativity. Unequal charge distribution

Polar Covalent Example HBr Electronegativity of H is 2.1 Electronegativity of Br is 2.8 Br pulls the bonding electrons toward itself Results in a polar bond. Br is slightly negative H is slightly positive