Chemistry- VSEPR & IMF

What are exceptions to the octet rule?

H only has to have 2 ve-, and B only has to have 6 ve-

What is the expanded octet rule?

Exceeds the octet rule, 10 or 12 ve- around the central atom, and elements in period 3 or greater can exceed the octet rule

What is the single covalent bond?

1 shared pair of ve-, 2 ve-

What is a double covalent bond?

2 shared pair of ve-, 4 ve-

What is a triple covalent bond?

3 shared pairs of ve-, 6 ve-

How do bonds and lone pairs situate themselves?

They orient themselves in a way to minimize repulsion, lone pairs have a greater repulsion than bonded pairs and that’s why bond angles get smaller the more lone pairs are present

What is molecular polarity?

Molecule that has a partially + and - side due to unequal distribution of e- because of different electronegative

What is a Dipole?

Name for the charged region on a polar molecule

What are polar molecules

e- are distrubited unequally because of different electronegatives, unsymmetrical, and one side is postively charged and the other is negatively charged

What is electronegative?

How much an element wants an e-

What is a nonpolar molecule?

E- are distributed equally, same electronegatives, have a netural charge, and symmetrical shape

How to tell if a molecular geometry shape is symmetrical or not?

Same atoms and evenly spaced out

What molecular geometry shapes are symmetrical?

Linear, tetrahedral, Octahedral, Trigonal Biyprimadal, and Trigonal planar

How to tell if a molecule is nonpolar?

1. The molecular shape around the central atom has no lone pairs

2. All atoms around the central atom are the same

What is vapor pressure?

How easily molecules escape a liquid into a gas

• Weak IMF: High vapor pressure

• Strong IMF: Low vapor pressure

What is evaporation?

Liquid molecules escape into the air

• They must overcome IMFS

• Weaker IMFS - easier escape - faster evaporation

• Only happens on the surface

• When fast molecules escapes, the liquid cools

What is Endothermic?

A process that absorbs energy (heat) from its surroundings

• Evaporation is endothermic because liquid takes in heat and so the area around it gets cooler because the heat goes into that process

How to check if a Lewis structure or compound is drawn correctly?

1. Check that each atom has full octets (expect for H that only needs 2 ve- and B that only needs 6 ve-, or if it’s in period 3 and greater and has an expanded octet)

2. Count the total number of valence electrons and if its more add double or triple bounds, less: add to the central atom

How to calculate the polarity of a molecule?

1. Draw the correct Lewis structure with the correct shape

2. Determine the bond dipole for each bond

3. Do the bond dipoles cancel out? Yes: Nonpolar, No: Polar

4. Do the bond dipoles have an overall direction? Yes: Polar (draw overall dipole for the molecule), No: Nonpolar

What is the charge of static electricity?

Negative

What is the polarity of Ethanol?

Polar

What is the polarity of Hexane?

Nonpolar

What is a chemical bond?

FOA between 2 atoms/ ions in a molecule due to sharing/transferring ve-

• Ex: Ionic, Metallic, and Covalent Bonds

• Harder to break apart than IMF

What is a IMF?

Attractive force between neighboring particles such as molecules through and determine the properties boiling point, vapor pressure, surface tension, and the strength of the actual bond

• Outside of the molecule compared to a chemical bond being inside of it

• Weaker than chemical bonds

• Diff Types: LDF, DD, HB

What is LDF?

Attractions between nonpolar molecules do this by having an induced dipole (weak, temporary), typically the weakest (the strength goes up as there are more electrons because it becomes more polarizable)

What is DD?

Attractions between polar molecules with permanent dipoles, partial positive region attracts to partial negative, typically has intermediate strength

What is Hydrogen Bonding?

FOA between polar molecules containing H bonded to F,O, or N, typically the strongest

What are the properties of LDF?

• Low Boiling Points

• Low Surface Tension: B/c molecules are held together less strongly

• High vapor pressure + Evaporation rate: B/c its weaker so the molecules escape easier

What are props of DD?

• Intermediate boiling point

• Intermediate Surface tension

• Lower vapor pressure + Evaporation rate

What are props of HB?

• Highest boiling point

• Highest surface tension

• Lowest vapor pressure + evaporation rate

What is surface tension?

How tight the surface of a liquid is because molecules pull on each other