Sunday, 27 May 2012

When atoms are bonding, they ofter bond with some angles. A simple theory that enables the chemist to correctly predict the geometries of most substances is the valence-shell-electron-pair-repulsion-theory. We can say that as VSEPR.

Basicly VSEPR will have three situtions.

1, Three atoms. Example BeCl2

Cl----Be----Cl      In this example, we calculate the angle between two non central atoms with the central atom.  Therefore the angle betwee Cl and Cl is 180. We call it LINEAR shape.

2, Four atoms. Example BF3

                     F     F
                      \    /
                        B
                        /
                       F                             The angle between F and F is 360/3=120
We call it Trigonal planar.

3, Five atoms. Explam CH4

                         H
                        /
                 H--C--H
                      /
                    H                                This one is special. When five atoms are bonding with a central atom. The angle will be 109.5

Tuesday, 22 May 2012

Organic Naming

Alright guys, this is gonna be Organic Naming - last blog of the year :)

Alkanes + Alkene + Alkyne

Contain the carbon chain with:
  • Alkane has single bond (replace "e" with "ane")
  • Alkene has double bond (replace "e" with "ene")
  • Alkyne has triple bond (replace "e" with "yne")
How to name:
  1. Count the longest carbon chain and come up with their name. ( methane, ethane ... )
  2. Find out if there's any branch attached to the chain
  3. Put the number indicates the branch's location in the carbon chain with the branch's name. Example: the methyl group locates in the 3 carbon of the chain --> 3-methyl
  4. If there are more than 1 group then remember to put them in alphabetical order
  5. If there are more than 1 same group at the same location, put their number of location including di, tri, tetra, penta ... Example: there are 2 methyl group at carbon 4 of the chain --> 4,4-dimethyl
  6. Combine it with #1
Example:
Here we see that the longest chain has 4 carbons with single bond --> butane
there's a methyl group at carbon #2 --> 2 methyl
==> 2-methyl butane

Halides (Halogen) and Nitro

Halides and Nitro are group that has halogen element as a branch or NO2 (nitro) as a branch
How to name:
  1. Follow exactly the rule above
  2. Replace the ending of the element's name with "o"
  • Br = bromo
  • Cl= Chloro
  • F= Fluoro
  • I= Iodo
  • NO2 = nitro

Alcohols

An alcohol is an organic compound that contains (-OH) functional group
 How to name: 
  1. Use the longest chain that contains -OH. 
  2. Replace the ending "e" by "ol". Example : Ethane --> Ethanol
  3. Remember to make sure that you're in the lowest number and alphabetical order
Example:
We can see that the longest chain is ethane and -OH is in the first C --> no need to write number
--> the compound's name would be Ethanol or 1-Ethanol 

Properties:
  • The -OH is an alcohol makes this compound soluble in water but then the hydrocarbon chain tends not to solute in water
  • And boys, alcohol is poisonous lol! 

Aldehyde and Ketone

Both are contain carbonyl ( =0 )

Aldehyde

Aldehyde has the double bond O at the beginning of the chain.
How to name:
  1. Find the longest chain of carbon, replace "e" by "al"
  2. Make sure that you're in the lowest number and alphabetical order
Example:
We can count that the longest chain that contain =O has 8 carbon --> Octane
But because of the =O --> replace "e" by "al" --> Octanal
There's no more branch so our compound name would be Octanal

Ketone

Ketone is basically the same as Aldehyde but it contains the =O anywhere in the middle of the chain.
How to name:
  1. Find the longest chain of carbon, replace "e" by "one"
  2. Make sure that you're in the lowest number and alphabetical order 
Example:
We count the longest chain that contains =O has 4 carbon --> butane
But the =O locates in the 2nd carbon of the chain --> it's an Ketone --> change Butane --> Butanone
Properties of Ketone and Aldehyde
  • Both are soluable
  • Aldehydes are very reactive, easily converted to Carboxylic Acids
  • Ketones are relatively unreactive

Carboxylic acids

Carboxylics are formed by and (=O) and (-OH) group
How to name:
  1. Follow the basic naming
  2. Replace the "e" in the longest chain by "oic" and "acid" at the end
  3. Make sure that you're in the lowest number and alphabetical order 
Example:
  1.  The longest chain has 4 carbons --> butane
  2. There's the (=O) and (-OH) branch attached --> it's an Carboxylic acid
  3. There's also the Chloro branch in the 3rd carbon and methyl brach in the 2nd carbon
  4. The compound's name would be 3 chloro 2 methyl butanoic acid
Properties:
  • Carboxylic acids can be neutralized with a base

Ester

Easters are basically the combination of Carboxylic Acids + Alcohol
How to name:
  1. Follow the basic naming rules
  2. Name the R' carbon chain first as normally ( methyl, ethyl ... )
  3. Then name the R carbon chain and replace an "e" ending with "oate"
Example:
We can see that the R' carbon chain has 3 carbons --> propyl
The R carbon chain has 1 carbon --> methane but it's an esters --> replace an "e" with "oate"
==> Propyl methanoate
Properties:
  • Ester have pleasant, fruity odors ...

Ethers

In ethers, Oxygen connects to 2 alkyl chain
 How to name:
  1. We follow the basic rule for naming
  2. Name the short chain first then the longer chain second
  3. The longer chain would be at last of naming ( basically alkyl )
  4. The shorter chain would be named at first, replace "e" by "oxy"
  5. basic ethers is methoxy methane
Example:

Properties:
  • Highly flamable
  • Insoluable in water
  • Good solvent for organic compound

Amines

Nitrogen bonds to H
How to name:
  1. Follow basic naming rules
  2. Add (-amino) with it's location in the carbon chain
  3. Ending with the longest carbon chain ( methane, ethane ..)
Example:
The longest carbon chain has 5 carbon --> pentane
The amino branch locates in the second carbon of the chain -> 2 amino
==> 2 amino pentane
Properties:
  • Soluable
  • Fishy odors
  • Amines are organic base that easily form salts when react with acid

Alicylics 

Use the same rule as Alkane and Alkene, just need to add "-cyclo" in front of the longest chain's name
The structure is gonna be ring, so depends on how many C in the longest chain, we would draw the appropriate ring
Example:
The ring has 6 carbons --> hexane
there are 3 methyl branches at location 1,2,3 
=> 1,2,3 trimethyl cyclohexane
Note: If there's a double bond or triple bond, have to start counting from the beginning of the double bond or triple bond so we can get the lowest number.

Aromatics

Is the ring that contain benzene.
Follow same rule as alicylics
If benzene appears as a branch, add "phenyl" otherwise just add benzene at the end of your compound's name
Ex: 1,2,3,4 tetraphenylpentane
Ex: 1,2 dimethyl benzene



NOTE: All of the naming must be in the lowest number and alphabetical order

Saturday, 19 May 2012

Lewis and Electron Dot Diagrams

Okay, most of you know the Bohr Model... right? Well Lewis models are sort of like Bohr Models but with only the valence electrons around them.
Valence electrons are.... Electrons in the outermost shell of an element or atom. Also called the "reactable electrons."
Sometimes Lewis diagrams are called dot structures because the diagram is made of dots, obviously.
So how do you draw a Lewis/ Dot Diagram?
Step One - What element are you drawing?? Count the electrons.
Step Two - Place the valence electrons around the element symbol.




For more information about Lewis Daigrams, check these websites out!
http://chemistry.about.com/od/generalchemistry/a/lewisstructures.htm
http://www.ausetute.com.au/lewisstr.html


Friday, 18 May 2012

Chemical Bonds and Electronegativity

There are 2 kinds of bonds...
Covalent bonds (Non- Polar Covalent bonding) - when electrons are shared EQUALLY. Bonding between non-metals (negatively charged).
Ionic bonds (Polar Covalent Bonding) - when 1 atom has a greater attraction for the electrons than the other atom. Bonding between non metals and metals
Electronegativity - the attraction of an atom towards its shared pair of electrons in a chemical bond.
^ Use me to help you understand more about electronegativity!!

To learn more about chemical bonds, check out these websites!