Covalent Bonding Sharing of Electron Pairs: Non-metal with Non-metal Atoms

Compounds that are NOT held together by an electrical attraction, but instead by a sharing of electrons. Occur between nonmetal atoms with electronegativity differences less than 1.67 Covalent Bonding

H Covalent Bonding

A neutral group of atoms joined together by covalent bonds is called a molecule. A compound composed of molecules is called a molecular compound. The chemical formula for a molecule is called the molecular formula. Covalent Bonding Molecule NameMolecular FormulaLewis Projection L-tryptophanC 11 H 12 N 2 O 2

Covalent Bonding Properties of Molecular Compounds: Composed of two or more nonmetals. Usually gases or liquids at room temperature. But can be found in any physical state at STP. Molecular compounds tend to have lower melting and boiling points than do ionic compounds. Do not conduct electricity. They form nonelectrolytes. in solution.

Covalent Bonding Reason: Molecular compounds do not break apart into ions in solutions. Do not conduct electricity. They form nonelectrolytes.

Covalent Bonding Reason: There are no (or few and weak) bonds holding the molecules together in molecular compounds. Molecular compounds tend to have lower melting and boiling points than do ionic compounds. Molecular Compound (H 2 O) Ionic Compound (NaCl)

intermolecular bonds Dispersion forces - caused by motion of electrons (weakest intermolecular force). More electrons = stronger dispersion forces. Diatomic halide molecules are held together by dispersion forces. gas liquid solid

intermolecular bonds dipole interactions

hydrogen bonds Weak bonds between bonded hydrogen and some electron dense species. (F,O,N)

polar covalent bonds Polar bonds have more electrons on one side of the bond than the other. Electrons concentrate around electronegative elements.

polar covalent molecules Polar molecules have polar bonds. A molecule with two poles is called a dipole.

non-polar covalent bonds

Covalent Bonding Predicting Molecular Geometries & Polarity: Atoms attain an octet (also called noble gas electron configurations) by sharing electrons. The bonds that form from this sharing can be single, double or triple. Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds.

How Do We Proceed ? 1.Determine total number of valence electrons 2.Based on usual bond numbers, identify reasonable layout for atoms 3.Place bonding electrons between atoms to make usual number of bonds 4.Place remaining electrons as lone pairs around atoms still lacking an octet Covalent Bonding

hybrid orbital geometries

H + C 1H1H 1e - 6C6C 2e - 4e - Equivalent to: H·H· · C · · · Outer e - only shown Covalent Bonding

H·H· · C · · · Outer e - only shown H·H· H·H· H·H· H + C Covalent Bonding

H:H: C Outer e - only shown H :H:H : : H 2 e - at each H 8 e - at carbon all atoms closed shell Positive nuclei Negative electrons H + C Covalent Bonding

H + C Final Structure: Tetrahedral Covalent Bonding

H·H· Outer e - only shown H·H· H·H· N · · · : H + N Covalent Bonding

N Outer e - only shown H :H:H H:H: : : 2 e - at each H 8 e - at nitrogen all atoms closed shell H + N Covalent Bonding

H + N Final Structure: Trigonal Pyramidal Covalent Bonding

H·H· Outer e - only shown H·H· O : · · : H + O Covalent Bonding

O Outer e - only shown H : H:H: : : 2 e - at each H 8 e - at oxygen all atoms closed shell H + O Covalent Bonding

H + O Final Structure: Bent Covalent Bonding

Outer e - only shown H·H· : F : · : H + F Covalent Bonding

F Outer e - only shown H : : : : 2 e - at H 8 e - at fluorine all atoms closed shell H + F Covalent Bonding

H + F Final Structure: Linear Covalent Bonding

Patterns for Major Elements: CH 4 C = 4 bonds; all electrons shared NH 3 N = 3 bonds; one lone pair H 2 OO = 2 bonds; two lone pairs HFF = 1 bond; three lone pairs Covalent Bonding

4 Bonds All e - shared 3 Bonds 1 Lone Pair 2 Bonds 2 Lone Pairs 1 Bond 3 Lone pairs Carbon, group IV Nitrogen, Group V Oxygen, Group VI Fluorine, Group VII Covalent Bonding Patterns for Major Elements:

Other Compounds Have Same Pattern: C = 4 bonds; Cl (like F) = 1 bond P (like N = 3 bonds; Br (like F) = 1 bond Covalent Bonding

S (like Oxygen) = 2 bonds, 2 lone pairs C = 4 bonds; O = 2 bonds, 2 lone pairs Other Compounds Have Same Pattern: Covalent Bonding

Multiple Bonds Atoms may share more than one pair of electrons a DOUBLE BOND forms when atoms share two pairs of electrons (4 e - ) a TRIPLE BOND forms when atoms share three pairs of electrons (6 e - ) Total number of bonds per atom unchanged Covalent Bonding

4 Bonds, each carbon Two bonds at oxygen C 2 H 4 Valence e - = 12 H 2 CO Valence e - = 12 Covalent Bonding Multiple Bonds

Total valence e - = 16 (Oxygen = 6 e -, each; Carbon = 4 e -. Four bonds/C; 2 bonds oxygen Total valence e - = 10 (H = 1, C = 4, N = 5) Bonds: C = 4, N = 3, H = 1 Total valence e - = 18 (O = 6, Cl = 7, P = 5) Bonds: Cl = 1, P = 3, O = 2 Multiple Bonds Covalent Bonding