Polar and nonpolar covalent bonds and molecules 16.3 Pages 460-463

Vocabulary Polar Nonpolar Dipole All have the word “pole” in it, meaning “a part of a system that has opposite positions” Ex: North Pole and South Pole refers to opposite locations and magnetic fields on earth. In chemistry Polar refers to oppositely charged sides of a molecule

Is sharing always equal? Main point- How bad do you want that item? In chemistry this is electronegativity.

Electronegativity determines the bond type We know the shortcuts for finding out the type of compound and bond formed. Metal with non-metal = ? Metal with metal = ? Non-metal with non-metal = ? This shortcut is really based on electronegativity (how much does one atom want the electrons of the other atom)

Electronegativity chart Actual values for each atom on page 405 H=2.1 Cl = 3.0 F= 4.0 C= 2.5 Na=0.9 Electronegativity difference Type of Bond Example 0.0 – 0.4 Nonpolar covalent H-H or C-H >0.4-1.9 Polar covalent H-Cl or H-F > 2.0 Ionic NaCl

Nonpolar covalent bonds When both atoms pull on the electrons equally, the electrons are shared equally. This happens when both atoms are the same (H2, O2, N2, Cl2, F2, Br2, I2) It also happens when both atoms have very similar electronegativity values Ex: C-H, C-C 2nd period ended here

Non-polar animation

Polar covalent bonds When the two atoms pull on the electrons unequally. The more electronegative atom will pull harder and acquire a slight negative charge The less electronegative atom will pull less and acquire a slight positive charge This is denoted by a delta (delta +, delta -)

Polar bond animation

Polar molecules A molecule with one side slightly positive and the other side slightly negative HCl HF CO H20 NH3 Not polar: CH4 does not have any polar bonds CO2 even though it has polar bonds

General Rule for identifying bonds as polar or nonpolar Same atoms on bond = non-polar bond C and H = non-polar bond Every other combination usually polar Sure solution: Look up electronegativities on page 405 and compare to table on page 463

HW: Fill out the table below Use the charts on p.405 and p.463 Bonded atoms Difference in electronegativity Polar or nonpolar covalent bond? H - H 2.1 – 2.1 = 0 Non-polar H - C H - O H - N C – C C - O C - N S - Cl O - N P - F Br - Br

What does the term “likes dissolve likes” mean in regards to polarity? Likes dissolve likes is a phrase that tells you which molecules will mix and which will not. Polar dissolves polar Nonpolar dissolves nonpolar Polar will not mix with nonpolar Demonstrate with a bottle that has oil and water in it Demonstrate with two beakers, one water, one oil, and 2 cubes of sugar in each one.

The 3 intermolecular forces 16.3 Pages 463-466

What does the prefix “inter” mean? “Intermolecular forces” means “Attractions between molecules”

Intermolecular attractions Atoms bond to have complete outer orbitals When they get there, they stop bonding and become the compound they become If only covalent bonds existed, each little molecule would be completely independent and every molecular compound would be a ? Gas! We would have no liquid!!!  So there must be OTHER interactions taking place between molecules…

The 3 weak intermolecular forces/attractions Van Der Waals Forces 1) London Dispersion forces 2) Dipole-dipole interactions 3) Hydrogen bonds- The strongest of the intermolecular forces

London Dispersion forces The electrons of a molecule will shift to one side, creating a temporary dipole. This dipole will cause the other molecule to create a dipole as well and attraction will occur for a very short time. This occurs between nonpolar molecules

Dipole-dipole forces The slightly positive part of one molecule will attract the slightly negative part of another molecule. This occurs between two polar molecules.

Hydrogen bonding The strongest of the 3 intermolecular forces A hydrogen covalently bonded to N, O, or F will be very electron deficient ( +) It will become attracted to an unshared pair of a different molecule. 2nd period ended here: review idea of H-bond being an H bonded to either NOF, attracted to an unshared pair of another molecule

Why does this matter? 1) Non-polar vs polar Polarity explains why water and oil do not mix!  Oil is non-polar, Water is polar Polarity explains why water dissolves ionic compounds!  1st period stopped with non-polar vs polar, ask them to know this (this is the real application of the theory)

Why does this matter? 2) Intermolecular forces Explain why liquids and solids exist!  Explains the melting and boiling points of molecular compounds. Hydrogen bonding explains why water has such high surface tension!  Helps DNA and proteins take the shapes that they take!  1st period stopped with non-polar vs polar, ask them to know this (this is the real application of the theory)

HW: 21) You find the difference in electronegativity between the atoms. <0.4 is nonpolar covalent 0.5-1.9 is polar covalent >2 is ionic 22) dispersion, dipole-dipole, hydrogen bond 23)CCl4 has polar bonds, but is not a polar molecule because of symmetry (it doesn’t have a (+) and (-) side. 24)HOOH, BrCl, HBr, H2O 26)shared bonding electrons, solubility ranges from high to low, exist as molecules

Polar bond – a covalent bond where electrons are shared unequally The more electronegative atom is slightly negative The less electronegative atom is slightly positive Non-Polar bond –a covalent bond where electrons are shared equally Both atoms have similar or identical electronegativity Dispersion – weak forces caused by the random motion of electrons The only attractions non-polar molecules can have Dipole-dipole – attractions between polar molecules The slightly positive end of one molecule attracts the slightly negative end of another Hydrogen bond – an attraction where a hydrogen (that is bonded to an N, O, or F) is attracted to an unshared pair of electrons on another molecule. The strongest intermolecular attraction of the three