Chapter 10 Chemical Bonding II Chemistry: A Molecular Approach, 1st Ed. Nivaldo Tro Chapter 10 Chemical Bonding II

Exceptions to the Octet Rule Incomplete Octets ---- Boron (6) Expanded Octets ----- Sulfur (sometimes), Iodine (12), Xenon (12), Phosphorous (10) Practice: BF3, ICl4, XeF4, PCl5

Structure Determines Properties properties of molecular substances depend on the structure of the molecule the structure includes many factors, including: the skeletal arrangement of the atoms the kind of bonding between the atoms ionic, polar covalent, or covalent the shape of the molecule bonding theory should allow you to predict the shapes of molecules Tro, Chemistry: A Molecular Approach

Molecular Geometry – Old News Molecules are 3-dimensional objects We often describe the shape of a molecule with terms that relate to geometric figures Number of Bonds attached to the central atom Number of Lone Pairs Around the Central Atom Shape of Molecule 2 Linear 1 Bent 3 Trigonal Planar Trigonal Pyramidal 4 Tetrahedral 5 Trigonal Bypyramidal 6 Octahedral Tro, Chemistry: A Molecular Approach

VSEPR Theory electron groups around the central atom will be most stable when they are as far apart as possible – we call this valence shell electron pair repulsion theory since electrons are negatively charged, they should be most stable when they are separated as much as possible Tro, Chemistry: A Molecular Approach

Tro, Chemistry: A Molecular Approach

The Effect of Lone Pairs lone pair groups “occupy more space” on the central atom because their electron density is exclusively on the central atom rather than shared like bonding electron groups this effects the bond angles, making them smaller than expected As a result, there is a second type of geometry known as the electron geometry. Tro, Chemistry: A Molecular Approach

Effect of Lone Pairs The bonding electrons are shared by two atoms, so some of the negative charge is removed from the central atom. The nonbonding electrons are localized on the central atom, so area of negative charge takes more space. Tro, Chemistry: A Molecular Approach

Tetrahedral-Bent Shape Tro, Chemistry: A Molecular Approach

Linear Shape Tro, Chemistry: A Molecular Approach

Describing the Geometry of Methanol Tro, Chemistry: A Molecular Approach

Polarity of Molecules in order for a molecule to be polar it must have polar bonds electronegativity difference - theory bond dipole moments - measured have an unsymmetrical shape vector addition polarity affects the intermolecular forces of attraction therefore boiling points and solubilities like dissolves like nonbonding pairs affect molecular polarity, strong pull in its direction Tro, Chemistry: A Molecular Approach

Molecule Polarity The H-Cl bond is polar. The bonding electrons are pulled toward the Cl end of the molecule. The net result is a polar molecule. Tro, Chemistry: A Molecular Approach

Molecule Polarity The O-C bond is polar. The bonding electrons are pulled equally toward both O ends of the molecule. The net result is a nonpolar molecule. Tro, Chemistry: A Molecular Approach

Molecule Polarity The H-O bond is polar. The both sets of bonding electrons are pulled toward the O end of the molecule. The net result is a polar molecule. Tro, Chemistry: A Molecular Approach

Molecule Polarity The H-N bond is polar. All the sets of bonding electrons are pulled toward the N end of the molecule. The net result is a polar molecule. Tro, Chemistry: A Molecular Approach

Molecular Polarity Affects Solubility in Water polar molecules are attracted to other polar molecules since water is a polar molecule, other polar molecules dissolve well in water and ionic compounds as well some molecules have both polar and nonpolar parts Tro, Chemistry: A Molecular Approach