Hydrogen Bonding

k so last class we started learning about molecular polarity and intermolecular bonds, but we didn't get the chance to get to hydrogen bonds so thats what we talked about the most today

• hydrogen bonding is a special type of dipole-dipole bond
• it occurs between hydrogen and nitrogen, oxygen and flourine

H-N, H-O, H-F

now just to recap all the the types of bonding forces:

• London Dispursion Force (L.D.F) is experienced by all molecules but is the weakest of bonds
• Dipole-Dipole is only present in some molecules, and is stronger than LDF
• Hydrogen Bonds are the strongest of all the molecular bonds and are only found in a couple of different molecules

one example we went through was putting some molecules in order of the strongest bond to the weakest bond. the ones we used were:

1. C2H5OH: 26 electrons and a bp of 78 degrees Celsius

2. CH3OH: 18 elestrons with a bp of 65 degrees Celsius

3. C2H6: 18 elesctrons with a bp of -89 degrees Celsius

4. CH4: 10 electrons with a bp of -161 degrees Celsius

now that we had finished talking about molecular bonds, we discussed ions in solutions for the rest of class

• dissociation is the splitting of ionic solids into ions
• there are multiple steps you must follow in writing a dissociation equation
• determine the ions that are in your ionic solid and plit them up on the other side of the equation from your original solid
• write (aq) next to the ions to show that they are now aqueous due to the fact they are dissovled in water
• find the charge of each of the ions and write it
• balance the equation using the charge of each ions to determine how many of them there should be

we went through some concentration examples that go back to our stoichiometry section, so its basically using our old knowledge to kind of figure out new examples. I won't write out the examples bacause they would just be WAY too confusing using blogger. but instead, i have an awesome video! YAY!

it says 20 second but its more like a minute and a half. still, this does a really good job of explaining hydrogen bonding!

thats all for now!

Molecular Polarity & Intermolecular Bonds

INTERMOLECULAR: intermolecular means the bonds are outside of the molecule

A. Polarity is the result of intermolecular bonds.
1) London Dispersion Force

• experience by all molecules
• results of electrons pushing on each other
• the weakest of all forces
• As the number of electrons increase LDF increases also

2)Dipole-Dipole

• Dipoles are partial separation of charges
• LDF is a type of temporary dipole
• Some molecules have a permanent dipole
• These are polar molecules
• Polarity is determined by electron affinity(how much an atom wants electrons)
• Electron affinity is called electron negativity
• Electron negativity is highest on the top right and lowest on the bottom left

• A bond between two atoms or molecules with different electron negativites result in a dipole-dipole bond.
• Dipole-dipole forces are weak versions of ionic bonds

EXAMPLES:
CHCl3 is polar because: its structural model is not symmetrical so that means it is polar.
C2H2Cl2 is both polar and non-polar depending on how you draw the structural model

Polar and Non Polar Solvents

Polar Substances have an unequal distribution of charges:


(if you were to draw a line down the middle of this diagram it would be symetrical)
Non-polar substances have unequal charge distribution (if symmetrical)


We did a lab that involved polarity and non-polarity. We mixed sugar, salt, and iodine with paint thinner and water and came to the conclusion that polar substances can combine with polar substances and non-polar substances can combine with non-polar substances but polar substances cannot combine with non polar substances.

Electrical conductivity in solutions requires charged ions to be transferred.
Iionic solutions dissociate or form ions so they always conduct.



Molecular substances do not usually dissociate.

follow the chart to determine conductivity:

Examples
element - yes/no - reason
Mercury - yes - metal
Carbon - no - solid non-metal
NaCl - yes - ionic
acetic acid - yes - acid
Iodine - no - not ionic/acid/base/metal