March 20, 2018 Polarity Bonding Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Do Now (4 min) When you boil water, which is occurring? March 20, 2018 Learning target: I can determine the polarity of compounds using lewis dot structures and electronegativity Do Now: (Answer on your Do Now Sheet) When you boil water, which is occurring? The water molecules are breaking apart into H and O The water molecules are separating into separate H2O molecules Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

What is a bond? A bond can be thought of as a force that holds groups of two or more atoms together and makes them function as a unit Example : water O Bonds require energy to break and release energy when made H H March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Types of bonds Ionic bonds - typically formed between metals and nonmetals Covalent bonds - typically formed between nonmetals Metallic bonds - formed between metals March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Covalent Bonds Covalent Bonds exist between nonmetals bonded together form when atoms of nonmetals share electrons electrons can be shared equally or unequally The unequal sharing results in polar molecules March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Types of Bonds Intramolecular bonds: Bonds that hold a molecule together (like holding the H to the O in H2O) Intermolecular bonds: Bonds that hold two or more molecules together (like holding one water molecule to another) March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Focus on Intermolecular Bonds Intermolecular Bonds – also called intermolecular forces, or IMFs We need to use Electronegativity March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Electronegativity Electronegativity values for each element are obtained by using the Periodic Table What is the trend for EN on the periodic table? March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

How can we tell really tell which type of bond we have? Electronegativity – how strongly an atom attracts electrons to itself This tells us what type of bond we have: Nonpolar Covalent, Polar Covalent or Ionic March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Electronegativity We take the difference between the electronegativity values to determine exactly what type of bond exists, in essence the polarity of the bond March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Determining Bond Polarity Look at the EN difference: < 0.5: nonpolar covalent bond (equal sharing) 0.6 – 1.6: polar covalent bond (unequal sharing) >1.7: ionic bond (transferring electrons) March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Bond Polarity Use your Reference Tables to determine the difference in electronegativity values and the type of bond for each of the following: H-H H-Cl H-O H-S H-F NaCl O2 KBr March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Lewis Structures Tell ALL When we draw CORRECT Lewis dot structures, we can decide whether molecules are symmetric or not… Symmetric: all surrounding atoms are the same Asymmetric: not all surrounding atoms are the same, there are lone pairs on the central atom March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Lewis Structures Tell ALL Let’s practice drawing Lewis dot structures: NH3 NH4+ CO2 H2O Which of the above are symmetric? March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Molecular Polarity You solved bond polarity with EN values You solved for the symmetry using Lewis dot structures Now, let’s find the molecule polarity March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Molecular Polarity Depends on 2 factors. Type of bonds in the molecule (polar or nonpolar) Arrangement of bonds or shape of molecule (symmetric or asymmetric) March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Diatomic Molecules Simplest case: Bond Polarity and Molecular Polarity are identical ex: H2 CO N2 HCl Larger Molecules – Have to look at how the bonds are arranged. March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

For larger molecules, look at the kind & arrangement of bonds to determine overall polarity of molecule. CH3Cl has 4 bonds. March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Polarity of Molecules To be POLAR: Polar bonds Asymmetric shape To be NONPOLAR: Nonpolar bonds OR - Polar bonds AND symmetric shape March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Symmetric Molecules Contain at least one mirror plane. March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Symmetric vs. Asymmetric CO2 is nonpolar. Can’t tell the ends apart. H2O is bent. Electron cloud is lopsided. H2O is polar. March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Polarity of CO2? Draw an arrow along each bond pointing to the more electronegative atom. If the arrows cancel out, the molecule is NONPOLAR. March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Polarity of H2O? The green arrows do not cancel out, so water is polar! March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Symmetry of Larger Molecules CF4 is fairly symmetric. Overall, it is nonpolar. The arrows cancel out. March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Molecular Polarity If you know the shape, you can use the arrow technique to determine the polarity. So how do you get the shape? March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Practice! Use the structural formula to predict Molecular Polarity! H  C  H   March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Practice CH4 C2H4 NO2+ H2S CH3Br March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Homework Complete the Everyday chemistry for Homework March 20, 2018 Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

Exit ticket (3 min) March 20, 2018 EXIT TICKET: Complete on a separate sheet of paper Determine whether CS2 is polar based upon lewis dot structure and EN Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity