Or how to be a greedy little atom POLAR COVALENT BONDS Or how to be a greedy little atom

Electronegitivity Electronegitivity: The ability of an atom in a molecule to attract electrons. (Table on pg. 320)

The big reveal… The electronegativity of a bond controls the type of bond atoms form: Electronegativity difference between bonding atoms: Bond Type: Zero Covalent Small to intermediate Polar covalent Large Ionic

Polar covalent bonds Covalent bonds share electrons, but not always equally.

Polar covalent bonds Electrons in a bond will spend more time near the atom with the highest electronegativity. This causes partial charges

Practice Which atoms in the following bonds are the most electronegative? HCl FBr H2­O CCl4

Practice Now draw the following molecules in VSEPR model form with partial charges. HCl FBr H2­O CCl4

End Day 1 HW: Molecular Polarity Worksheet

Polar Covalent Bonds These are called Polar Covalent Bonds. Covalent because they are sharing electrons. Polar, because they have ends (positive and negative). A more polar has a greater difference between the electronegativity values of the two atoms making the bond. Arrange the following bonds in order of increasing polarity: F-H, N-H, H-H, O-H, B-H

Arrange the following bonds in order of increasing polarity: F-H, N-H, H-H, O-H, B-H

Polar Covalent Bonds Day 2 Dipole moments Due to different electronegativity values, covalent bonds do not always share electrons equally. This causes certain atoms in a polar covalent molecule to be slightly negative and others to be slightly positive.

Dipole Moment Examples  Write the Lewis dot structure for HF, then the shape, and finally label the charges. Notice one side of the atom is more positive while another side is more negative. To show one side is more “+” than the other we are going to draw an arrow from the center of positive charge to the center of negative charge. We call this the Dipole Moment.

Dipole Moment Examples Example 2: H2O Write the Lewis dot structure. Now draw the VSEPR Shape. Make sure to write the O and H’s where they are located. Now label each atom in the VSEPR shape with its charge. Draw the dipole moment.

Practice Note: If there is not one side more positive or negative than the other, there is no dipole moment. H2 FCl SF2 CH2Cl2

Homework: Part 1: Add the dipole moment to last nights HW Read 11.1-11.3 Part 2: Answer Q/P: #5-11, 13

Effect on Physical Properties: The more polar a bond, the bigger difference in charge. The more difference the charge, the greater attraction to other molecules around it.  IMFA: Intermolecular Forces of Attraction (or how attracted are the molecules are to each other).

Bond Type: Charges: Strength of IMFA Ionic +, - Strong Polar Covalent slightly +, slightly – Medium Covalent none weak/none

Effect on Physical Properties These charges cause the different molecules to be attracted to each other. In Ionic (strong): this forms the crystal lattice In covalent (weak/none): London dispersion (tomorrow) In polar covalent: (draw picture on board)   The opposite side (+/-) of polar covalent molecule cause them to be strongly attracted to each other. The more polar = the stronger the attraction. This causes a higher boiling point.

Effect on Physical Properties Difference in Electronegativity Examples Type of Bond Charge Strength of IMFA (attraction) Boiling Point None N2, O2, H2 Covalent Low Very Low Medium/varies H2O, CO2 , CH4 Polar Covalent Partial +/- Medium High NaCl, MgF2 Ionic Full +/-   Solubility: Polar covalent or Ionic compounds can only dissolve into polar covalent liquids. Covalent molecules can only dissolve in non-polar liquids (Covalent liquids). https://www.youtube.com/watch?v=nVr9WdPjJ-s

Homework Polarity Worksheet

Effect on Physical Properties Difference in Electronegativity Examples Type of Bond Charge Strength of IMFA Type of IMFA Boiling Point None N2, O2, H2 Covalent Low London Dispersion Very Low Medium/varies H2O, CO2 , CH4 Polar Covalent Partial +/- Medium Dipole-Dipole, Hydrogen Bonds High NaCl, MgF2 Ionic Full +/- Ionic Bonds