Covalent Bonding Sharing of Electron Pairs: Non-metal with Non-metal Atoms
Covalent Bonding • 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••H
Covalent Bonding
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 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 Do not conduct electricity. They form nonelectrolytes. • Reason: Molecular compounds do not break apart into ions in solutions.
Covalent Bonding Molecular compounds tend to have lower melting and boiling points than do ionic compounds. • Reason: There are no (or few and weak) bonds holding the molecules together in molecular compounds. Molecular Compound (H2O) 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 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.
Covalent Bonding • How Do We Proceed? Determine total number of valence electrons Based on usual bond numbers, identify reasonable layout for atoms <VSEPR> Place bonding electrons between atoms to make usual number of bonds Place remaining electrons as lone pairs around atoms still lacking an octet
hybrid orbital geometries
hybrid orbital geometries
Covalent Bonding · · · C · Outer e- only shown H + C 1e- 2e- 1H 6C 4e- Equivalent to: H·
Covalent Bonding · · · C · H + C H· H· H· H· Outer e- only shown
Covalent Bonding H + C Positive nuclei H 2 e- at each H : H: :H C : H Negative electrons 8 e- at carbon all atoms closed shell Outer e- only shown
Covalent Bonding H + C Final Structure: Tetrahedral
Covalent Bonding : · · N · H + N H· H· H· Outer e- only shown
Covalent Bonding H + N 2 e- at each H : H: :H N : H 8 e- at nitrogen all atoms closed shell Outer e- only shown
Covalent Bonding H + N Final Structure: Trigonal Pyramidal
Covalent Bonding : O : · · H + O H· H· Outer e- only shown
Covalent Bonding H + O 2 e- at each H : H: : O : H 8 e- at oxygen all atoms closed shell Outer e- only shown
Covalent Bonding H + O Final Structure: Bent
Covalent Bonding : : F : · H + F H· Outer e- only shown
Covalent Bonding H + F 8 e- at fluorine all atoms closed shell : : : F : H 2 e- at H Outer e- only shown
Covalent Bonding H + F Final Structure: Linear
Covalent Bonding Patterns for Major Elements: • CH4 C = 4 bonds; all electrons shared • NH3 N = 3 bonds; one lone pair • H2O O = 2 bonds; two lone pairs • HF F = 1 bond; three lone pairs
Covalent Bonding Patterns for Major Elements: 4 Bonds All e-shared • Carbon, group IV 3 Bonds 1 Lone Pair • Nitrogen, Group V 2 Bonds 2 Lone Pairs • Oxygen, Group VI 1 Bond 3 Lone pairs • Fluorine, Group VII
Covalent Bonding 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 Other Compounds Have Same Pattern: S (like Oxygen) = 2 bonds, 2 lone pairs C = 4 bonds; O = 2 bonds, 2 lone pairs
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 Multiple Bonds • C2H4 Valence e-= 12 • H2CO 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
