Polarity and Intermolecular Forces of Attraction Covalent bonds

+ Polarity and Intermolecular Forces of Attraction

+ Covalent bonds mean sharing electrons between atoms…but it isn’t always FAIR/equal. Fluorine LOVES TO GRAB electrons Hydrogen ends up with less electrons

+ This ability to attract electrons to itself is called ELECTRONEGATIVITY Electronegativity is the ability of an element to attract bonding pair of electrons in a chemical bond.

+ The periodic table can help us see that going towards Fluorine means increasing electronegativity

+ When a bond is POLAR this means we have a partial (+)/electron-poor and a partial (-)/electron-rich area.

+ Polar Bonds and Lone Pairs contribute to polarity but we need to see if they add or cancel each other. AXE notation?

+ Polar Bonds and Lone Pairs contribute to polarity but we need to see if they add or cancel each other.

+ Exercise: 1. Draw the proper Lewis Structure of a. SOCl 2 b. H 2 S c. HCN Electronegativity Values: S = 2. 5 O= 3. 5 Cl = 3. 0 H= 2. 1 C = 2. 5 (4. 0 = most EN) 2. Give AXE notation for geometry and identify the shape 3. Show polarities of bonds 4. Determine if the molecule is polar OVERALL or not.

+ Know that we know if our molecules are polar or not, we can know a lot more on how substances behave!

+ On the basis of attraction of opposite charges, we can list down ways molecules can interact:

+ Ion-dipole interactions: a permanently charged ion attracts a polar molecule (called a dipole since it has both +/- ends, di- means two, so two-poled)

+ Ion-dipole interactions

+ Dipole-dipole, or simply called polar interactions are the next strongest…

+ Dipole-dipole, or simply called polar interactions are the next strongest… Sucrose (table sugar) ethanol

+ A special strong version of a dipole interaction is called HYDROGEN BONDING

+ Hydrogen bonding is ESSENTIAL TO LIFE… keeping our proteins, cells, tissues, organs all structured and functioning.

+ The next interactions, slightly weaker are the ions or dipoles with INDUCED DIPOLES n. INDUCED DIPOLES – a non-polar molecule that has its electrons slightly affected by polarity of another polar molecule (dipole) n. It’s like you have a metal object become magnetic too when you put a magnet against it.

+ The weakest intermolecular force of attraction is called DISPERSION FORCES n Think of it as induced-dipole induceddipole. n Molecules have electrons around them, but in blobs that can change. They aren’t orbiting the nucleus in fixed orbits. n If the electron cloud/blob changes shape a bit, it becomes slightly polar.

+ Dispersion forces or non-polar interactions ARE VERY IMPORTANT AS WELL. They can be seen as negative polar-polar interactions.

+ Dispersion forces, are vital in so many ways…

+ All these IMFAs (intermolecular forces of attraction) explain so many things around us! SOLUBILITIES…

+ Why isn’t caffeine very soluble in water?

+ All these IMFAs (intermolecular forces of attraction) explain so many things around us! MELTING POINTS/ BOILING POINTS Explain why acetone boils/evaporates more easily than water even though it is a heavier/bigger molecule. ACETONE: 56°C WATER: 100°C

+ All these IMFAs (intermolecular forces of attraction) explain so many things around us! MELTING POINTS/ BOILING POINTS: Both use weak dispersion forces but why do they still differ in boiling points?

+ Soaps use 2 different IMFA’s: Iondipole interactions and NONPOLAR/Dispersion forces ION-LIKE HEAD. With a negative charge RED = Oxygens NON-POLAR TAIL. . Black = Carbon White = hydrogen

+ The polar/ionic head of soap is called HYDROPHILIC (water-loving) and the nonpolar tail is called HYDROPHOBIC (water-fearing)

+ Superhydrophobic surfaces use nano-structures on their surfaces to create the lotusleaf effect.