Chapter 6 The Shape of Molecules

Are all Covalent Bonds Created Equal? Electronegativity (E.N.) causes different types of covalent bonds! High EN= greater ability to take electrons Nonmetals … Metals … Metals can lose electrons to nonmetals to form ionic bonds…but what happens with two nonmetals?

Electronegativity (E.N.)

Covalent Bond Classification Electronegativity and Covalent Bond Types Two atoms with identical E.N. result in pure covalent bonding… Which means.. Different E.N. causes polar covalent bonding… Which means…

Covalent Bond Classification Electronegativity difference (EN) Relationship between EN and bond polarity:

Classifying Bonds based on EN Greater EN means more polarity EN difference below 0.5 = EN Difference .5- 1.9 “ish” = EN difference greater than 1.9 =

Classifying Bonds based on EN Classify the bond type of the following compounds based on EN difference H2O (between one H and the O) NH3 (between one H and the N) Cl2 RbCl Which has the greatest ionic character? Which is most polar? Which has the greatest covalent character?

6.2 Valence Shell Electron Pair Repulsion (VSEPR) Theory Valence shell electron pair repulsion theory Bond type does not fully determine shape! VSEPR Model is used to predict three-dimensional shapes of molecules. Based on how negative charges on electrons repel one another… the electrons move as far apart as possible!

Steps in using VSEPR theory: Draw the electron dot diagram Find the steric number for the atom Predict the molecular shape… SN of 4 = tetrahedral SN of 3= trigonal planar SN of 2 = linear 4. Account for lone (non-bonding) pairs SN 4, one lone pair = PYRAMIDAL SN 4, two lone pairs= BENT SN 3, one lone pair= BENT

6.2 VSEPR Theory

6.2 VSEPR Theory

6.2 VSEPR Theory Methane (CH4) How many bonding electron pairs? Steric number = ___________, ____________ What shape? Why?

6.2 VSEPR Theory Predict the shape of NH3 1. Draw the electron dot diagram. 2. Find the steric number for the atom. 3. Predict the maximum angle. But…

Molecular Polarity= distribution of electrons 6.3 Polarity of Molecules Molecular Polarity= distribution of electrons Related to bond polarity but not the same Related to the molecule shape: Even electron distribution= Uneven electron distribution = Polar molecules: Nonpolar molecules:

Consider bonding in H2 and HF 6.3 Polarity of Molecules Consider bonding in H2 and HF H2 is _______________________ HF is ______________________ Describe the e arrangement on each: Describe the partial charges on each:

6.3 Polarity of Molecules Molecular polarity H2 is a nonpolar molecule Electrons are equally distributed, even charge HF and HCl are polar molecules Why? How?

Showing molecular polarity 6.3 Polarity of Molecules Showing molecular polarity Dipole moment vectors: Long arrow means:

Dipole moment and molecular polarity 6.3 Polarity of Molecules Dipole moment and molecular polarity Dipoles in an asymmetrical molecule don’t cancel What’s this mean? Dipoles in linear or symmetrical molecules cancel out because they go in opposite directions

6.3 Polarity of Molecules Determine if each of these is polar or nonpolar… Phosphorus trichloride Ammonia (nitrogen trihydride) Ethene C2H4 (don’t forget the C=C)

6.2 Valence Shell Electron Pair Repulsion (VSEPR) Theory (Continued) PBr3 Draw the Lewis Structure with electron groups Find the SN Determine the electron arrangement shape Determine the true molecular shape