Monday, June 6, 2011

Organic Chemistry

Organic chemistry is the chemistry of carbon compounds. It is responsible for many of the every day products that are used around the world.
Some examples:

  • clothing
  • all plastics
Properties of organic compounds
  • low melting points
  • weak or non-electrolytes
  • can form chains of carbon atoms that are linked in a 
    • Straight line
    • circular pattern
    • branched pattern
  • can link with other atoms in a

Alkanes (unbranched/straight chain) 
A hydrocarbon is a compound that contains only hydrogen and carbon; there are diff. types of hydrocarbons, and diff. ways to represent them.
Alkanes are saturated hydrocarbons which have carbon atoms bonded by single bonds
-saturate: not possible for another atom to bond to the structure
Naming an alkane is pretty simple. The names of hydrocarbons end in "-ane" because they are alk-ANE-s. 

Here's a video on naming the first 10 alkanes

Alkyl Groups
-these are alkanes that have lost one hydrogen atom
if there are more than one of the same kind of alkyl group, use the prefix "di", "tri", "tetra" etc. 


Functional Groups

Functional Groups are organic compounds that can contain elements other than Carbon and Hydrogen.
A functional group may be a single atom (such as F, Cl, Br, or I), or groups of atoms (such as NO2, NH2).
There are 4 types of functional groups.

  • Alcohols
  • Halides (halogen) or Nitro
  • Aldehydes
  • Ketones
Halides and Nitro Compounds
Halogen and Nitro compounds can be attached to all alkanes, alkenes, and alkynes. 
The main chain name will receive one of the following prefixes if the appropriate group is attached.
Fluorine -> Fluoro
Chlorine -> Chloro 
Bromine -> Bromo
Iodine -> Iodo

...and so on. As you can see you just replace the "-ine" with "-o". 

Properties of Halogenated Compounds
  1. Compounds containing F, Cl, Br, and I are generally insoluble in water.
  2. Fluorinated hydrocarbons are unreactive.
  3. Compounds containing Cl or Br are more reactive, but only in drastic conditions.
  4. Compounds containing I are extremely reactive. 
Properties of Nitro Compounds 
  1. Normally insoluble in water.
  2. Unreactive to chemical attack, except under drastic conditions.
  3. Tend to be explosive.
  4. Generally have a pleasant odor. 
Alcohol
Alcohol is an organic compound that contains an -OH (hydroxyl) functional group. 
Alcohols are named by using the longest carbon chain containing the OH group, and replacing the "-E" ending in the parent hydrocarbon chain with the ending "-OL".

Properties of Alcohols
  1. Soluble in water, but hydrocarbon chain tends to be insoluble in water.
  2. All alcohols are poisonous in some degree. 
What happens if there's more than one OH? 
If a compound has more than one -OH group, number both and add the prefix ending. "-diol", "-triol", etc. 

Check out this video that sort of explains alcohols in a catchy rap.
Alcohol Rap

Aldehydes 
An Aldehyde is a compound that has a double bonded oxygen at the end of a chain. 
Change the parent chain ending to "-al". Be careful! Don't confuse this with alcohol! 
Here's a quick video on aldehydes.

Ketones
Ketones are hydrocarbon chains with double bonded oxygen that is NOT on either end.
Add "-one" to the parent chain.

Properties of Aldehydes and Ketones
  1. Both partially soluble in water.
  2. Aldehydes are very reactive.
  3. Ketones are relatively unreactive. 
Here's another video, this time on Ketones 

And finally, the last video I'm going to show you is a video on ALL functional groups!



Thursday, June 2, 2011

Bonding

There are 3 types of chemical bonds

Ionic bonds: the transfer between 2 atoms to form a positive and negative ion.
Non-polar covalent bonds: equal sharing of electrons
Polar covalent bonding: unequal sharing of electrons



Ionic bonding uses an electrostatic force. That is the force that exists between particles that are charged as a result of attraction or replusion. (remember, opposites attract? Opposite charges attract and like charges repel). These bonds are very strong and have a high melting temperature.

So, I know you guys have a burning question:

Why do things lose valence electrons? This is explained by electronegativity. Metals have low electronegativity and non-metals have high electronegativity, as we learned in the last chapter. The electronegativity decreases to the right across the periodic table. The difference in the electronegativity will determine the electron sharing and determine if it is equally shared or unequally shared.

Here is how to figure that out! This is the formula:

ENeg Diff.= [ENeg1 - ENeg 2]

If it is a non polar covalent bond, the difference will be <0.5
If it is a polar covalent bond, the difference will be >0.5 and <1.8
If it is an ionic bond, the difference is >1.8


If ENeg Diff <0.5 it's a non polar covalent bond

If ENeg Diff > 0.5 and <1.8 it's a polar covalent bond

If ENeg Diff > 1.8 it's an ionic bond




Lets try an example:

Arsenic and Sulfur
Arsenic is 2.18 and Sulfur is 2.58. |2.18-2.58| = 0.40, therefore it is covalent.

Cobalt and Bromine
Cobalt is 1.88 and Bromine is 2.96 |1.88-2.96| = 1.08, therefore it is a polar covalent bond./

To draw diagrams of the compounds, draw the central atom in the middle and distribute the remaining atoms around it. Draw arrows indicating the direction of the polarity. Draw the partial positive and partial negative charges.

Partial Positive sign is the almost 8 but cut-off sign with a +
Partial Negative sign is the same thing but with a -


What is polarity?
Different Kinds of Bonds

Alkenes and Alkynes

Here are some basic facts:

-Carbon can form double and triple bonds with Carbon atoms
-When multiple bonds from fewer hydrogens are attached to the carbon atom

Alkenes

Alkenes are simply hydrocarbons with one or more double bonds located between carbon atoms leading to an "unsaturated hydrocarbon."

For example: CH2 = CH2 Ethene
CH2 = CH - CH3             1-propene or propene


                                                                            Ethene
Naming Rules:

1) Find the longest chain and place it at the end of the name
2) Number the carbon atoms to get the lowest number for the start of the double bond and place that number before the parent name
3) Assign names and numbers for all side groups and assemble the name alphabetically

Difference between cis and trans:
Cis = both on top or bottom
Trans = one on top and one on bottom


Alkynes

Alkynes are simply hydrocarbons with one or more triple bonds located between carbon atoms leading to an "unsaturated" hydrocarbon

The ending is changed from one of the alkanes and alkene for alkenes to "yne" for alkynes


Same naming/drawing rules apply!


Still feeling confused? Here are some helpful videos: