VSEPR Theory

What does VSEPR Theory stand for?

Valence-Shell Electron-Pair Repulsion Theory

What does it do?

It helps us to predict the geometries of most substances with 3D models.  In other words, it indicates the position of electrons surrounding the nucleus in a molecule.  To do so, we need to first assume that LIKE CHARGES REPEL each other.

How many scenarios are there?

There are three scenarios:

1) all of the electrons pairs in a molecule are shared

2) bonded electron pairs and lone electron pairs are present in the molecule

3) multiple bonds are present in the molecule

Scenario #1: When all of the electrons pairs in a molecule are shared, then...

It can be LINEAR with 180 degree angle between the two identical non-metals.  Example: BeF₂
It can be TRIGONAL PLANAR with 120 degree angles.  Example: SO3
It can be TETRAHEDRAL with 109.5 degree angles.  Example: CH<sub>4


Scenario #2: When bonded electron pairs and lone electron pairs are present in the molecule, then...


A decrease in bond angles will be due to the result of the increased electron-electron repulsion


It can be TRIGONAL PYRAMIDAL with 107.5 degree angles and 1 lone electron pair.  Example:</sub> NH_{3
It can be ANGULAR (BENT) with 118 degree angles and 1 lone electron pair.  Example:} SO2
_{It can be ANGULAR with 104.5 degree angles and 2 lone electron pair.  Example:} H₂O


_{Scenario #3: When multiple bonds are present in the molecule, then...}


There will be double bonds and triple bonds present.  Bond angles will decrease due to the multiple bonds as the electron cloud of a multiple bond takes up more space than single bond electron cloud.


It can be FORMALDEHYDE with 115.8 degree angle and 122.1 degree angle. (well, this scenario do not need to be worried as it is kind of like an enrich)




_{Finally, here is the golden summary of all the VSEPR models!!!}

Note: for our BC chem 11 curriculum, we only need to know: linear, trigonal planar, bent, angular, tetrahedral, and trigonal pyramidal.

Helpful resources and practice question websites:

http://misterguch.brinkster.net/VSEPR.html

http://chemprof.tripod.com/vsepr.htm

http://library.thinkquest.org/C006669/data/Chem/bonding/shapes.html

Here's a video of all the VSEPR model, watch it for... relaxation during study break... :)

Good luck studying! :D

Functional Groups

They are organic compounds made up of elements other than carbon and oxygen

Generally make up the most reactive part of the molecule
Can be either single bonds or group bonds
Single added atoms are generally called HALOGENATED COMPOUNDS, while grouped atoms are NITRO COMPOUNDS.


HALOGENATED:
F: fluoro
Cl: chloro
Br: bromo
I: iodo
General trend:

-Do not dissolve in water
-Hydrocarbons with fluorine are I reactive
-Hydrocarbons with chlorine and bromine are reactive, but only in drastic conditions
-Hydrocarbons with iodine are very reactive

1,3-dibromo-1,1-difluoropropane

NITRO:
NO2: nitro
General trend:
-Usually insoluble in water
-Generally do not react
-Explosive
-Usually have a pleasant odor
**naming**
Follow the same rules as simple hydrocarbons. Can be combined with alkanes, alkenes and alkynes. If there are multiple groups, precede with the prefixes mono-, di-, tri-, tetra-...

2,2-dimethyl-3-nitrobutane

ALCOHOL:
Organic compounds containing hydroxide (OH)
General trend:
-Poisonous to some degree
-While OH is soluble in water, the hydrocarbon chain is not. The longer the chain, the less soluble in water it is.
**naming**
Replace the ending "e" with the suffix "-ol"
If there are multiple, add the previous mentioned prefixes before the "ol" (1 hydroxide bond: propanol. 2 hydroxide bonds: 2,3-propanediol • the "e" remains if there are multiple • identify the placement of the OH with preceding numbers.

Hexanol

ALDEHYDES:
Contains carbonyl (a double group)
Has a double bonded oxygen at the end of the chain
General trend:
-Partially soluble in water
-Very reactive
**naming**
Replace "e" at end with -al suffix
Simplest form: methanal

Ethanal 

KETONES:
Double bonded carbon not at end of the chain
General trend:
-Partially soluble in water
-Unreactive
**naming**
Replace e ending with -one suffix

Propanone

CARBOXYLIC ACIDS:
Has a double bonded oxygen and hydroxide at end of chain.
General trend:
-Can be neutralized when placed with an acid.
**naming**
Drop the "e" and replace with -oic acid
Simplest form: methanoic acid

4-bromo-2fluorobutanoic acid

ESTERS:
oxygen bond dividing an acyl from an alkyl. Has a double bonded oxygen attached to closest carbon to oxygen
General trend:
-Pleasant smell
-Can be converted back into alcohol and carboxylic acid
**naming**
Alkyl: name using same rules
Acyl: (the remainder) replace -oic acid suffix of the corresponding carboxylic acid with -oate

Propyl Heptanoate

ETHERS:
Oxygen group connecting two alkyl groups.
General trend:
-Highly flammable
-Insoluble in water
-Makes a good solvent for organize compounds
-Certain compounds (ethoxy ethane) have anesthetic properties
**naming**
O is where side group counting begins
Follow all basic rules, but replace -yl with -oxy to the side group names

1-bromo-2-ethoxy hexane

AMINES:
Contains nitrogen compounds bonded to either hydrogen or carbon
General trend:

-Organic bases ➡ form salts easily when reacted with water
-Closely related to NH3
-Fishy odor
**naming**
Follow standard rules, but the longest chain name is preceded by amino.
As always, prefix numbers are used to identify the location of the amine.

ALCYLICS

Can form cycloalkanes, cycloalkenes and cycloalkynes. Forms a ring with carbons, either a branch or a main chain. Will also support other branches

General trend:

-Less stable (more reactive)

-can be branched

**naming**

numbering can begin anywhere, and go any direction

lowest chains possible

1. count total carbons, and name accordingly. Add cyclo prefix

2. if there is only one side group, it is assumed to be one, and no number is needed

3. If there are multiple, name the first group with number 1

4. side groups are named following basic rules

5. for alkenes, alkynes the bond is assumed to be the first, and no number is needed unless there are multiple

6. if the side groups are tied, give the lowest number to the first alphabetically ordered group

1-ethyl-2-methylcyclohexene

AROMATICS

contains a benzene ring

General Trend:

-Electrons are "delocalized" meaning that they can change position through the ring

-All of the carbon bonds therefore have the same reactivity

-Less reactive that cycloalkenes/ynes

-Because of the delocalization, benzene is very stable

Has a special diagram because of the free movement of electrons

Benzene

**naming**

When it is the main chain, just name the side groups attached to it, followed by benzene

If it makes up a side group, then it is called phenyl.

4-bromo-1-chloro2-ethyl benzene

Still unclear? Watch this YouTube video

Alkenes and Alkynes

Alkenes = double bonds
Alkynes = triple bonds

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

ending: change '-ane' to '-ene'

general formula: CnH2n

Geometric Isomers

-same chemitrical formula different geometry

-either cis or trans

larger group are above or below = cis

larger group are across the plane of the bond = trans

if no geometric isomers no need for cis or trans

Alkynes

-triple bonds

ending: change '-ane' to '-yne'

Eg.

4-methyl-2-pentyne

Organic Chemistry

The chemistry of CARBON compounds
PROPERTIES
-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:

• single bonds
• double bonds
• triple bonds
• versatility of organic compounds makes it such an important branch of chemistry

Alkanes

-straight/unbranched chain

hydrocarbon: a compound that contains only hydrogen and carbon. 

-non-polar molecules ==> immiscible with water

-Geometry: Tetrahedron

-saturated hydrocarbons bonded by single bonds

• Saturated: not possible for another atom to bond to the structure

-naming: "-ane" endings because they are Alkanes

homologous series: a series of organic compounds with a similar general formula, possessing similar chemical properties

meth = 1

Eth = 2

Prop = 3

But = 4

Branched Hydrocarbons

-"side branches" = hydro chains

• called substituted hydrocarbons or branched hydrocarbons

ending: "-yl"

-Alkyl group: an alkane which LOST one hydrogen atom

Ex 2-methylpentane

Rules for naming:

1) find and name the longest continuous carbon chain and place at the end of the name

2) Identify and name groups attached to this chain

3) number the chain consecutively, starting at the end nearest a side group

4) designate the location of each side group by an appropriate #

5) Assemble the name in alphabetical order

Electronegativity and Polarity

Hello all, and welcome to one of the less interesting blogs that we have to offer you.  Unfortunately it is important information so we'll try to make it as short and sweet as possible.  This is an electronegativity chart showing the charges for how easy/hard it is for each of these elements to loose an electron(s).  For instance, elements like Cesium is much more likely to give away its electron to another element (such as fluoride).  Make sense so far?  I hope so.














These charges can be used to determine what kind of bond you are looking at.  So, for example, you were looking at what kind of bond sodium and chlorine would make.  You would find their electronegativity difference.  


Na= 0.9                                              3.0-0.9= 2.1
Cl= 3.0
(if you get a negative answer, then think of what you have as having absolute value bars around it, just make it positive)
Based on this chart...and on prior knowledge, we know that this is an ionic bond.  However, when you do the same process with say, Nickel and oxygen, you will see that it instead comes up as a covalent bond.  That is something that will be explained more next year.

Here is the promised video to help keep the difference between the three rememberable.  If you can't deal with bad corny science songs, then don't click play.  Otherwise, I hope it helps!
http://www.youtube.com/watch?v=oNBzyM6TcK8

Part 2: knowing how to draw these.

Luckily, for the most parts, it is drawn as a regular lewis dot structure; which you already know how to do right? Right.  The only difference, is you need to indicate which atoms would become positive (loose electrons)  and which would be come negative (gain electrons)  Then draw an arrow pointing toward the negative one.  Have no idea what is being said, well, here is a nice long video that takes you back to periodic trends and explains it a bit more.

Best of luck :)

Chemical Bonding

Here starts the tedious introduction blog of the last unit we will do this year.  Many things that are mentioned here will come up later so if you don't understand this one....take the time to figure it out.

Electrostatic Force

Is a force existing as a result of the attraction or repulsion (two positive or two negative particles repel each other but one of each attract each other) between two charged particles.  It is a important to remember all bonds are based on the electrostatic relationships formed between particles.  When these particles are farther from each other, the attraction is greater.  If there is more charge, then there is more force.  This lovely force that occurs acts in all directions which is why that in both theory and practice, bonds can be made on any electron in the valance shell.  

Ionic Bonds

Ionic bonds are formed between positive and negative ions (most often medal and non-medal).  In an ionic bond, the electrons are transferred from what atom to another.  If you need a good way to remember that, just look at the chemistry cat on the side of our blog.  These bonds are always made to have a closed shell.  Ionic bonds are:

• very strong
• have high boiling points
• high electronegativity
• ionization energy

After the bond, all atoms become ions.  The positive ions are called cations and the negative ions are called anions.  

Then there is the crystal lattice...

In a crystal lattice, the ions in the bonds line up so the positive side of one molecule line up with the negative side of the next.  This is what allows them to connect and make things such as table salt. 

[Non-Polar] Covalent Bonding

These bonds, unlike ionic bonds, share their electrons amongst that atoms in the molecule.  As a result of this, the electrons are stuck in the middle between the two atoms.  These bonds tend to be very strong with lower melting points.  

Individual Molecules

Individual molecules are actually quite strong.  During melting, it is not the molecules themselves breaking apart, but the different molecules breaking apart from each other.  They are held together only by the intermolecular force.  This is especially true for covalent bonds.

The next blog will have a video that will help to remember the differences between the three.  (Yes, there is one more; covalent bonds aren't always non-polar...)

A Brief History of the Atom

Democritus: Everything is made up of infinitely small particles. Titled it atomos, meaning indivisible.

Dalton: Created modern atomic theory. All atoms are hooked together, and form specific ratios. Did not realize that atoms are made up of different particles

Thomson: Discovered electron with cathode ray tube. Applied a magnetic force, and noticed that the ray deviated, due to opposing magnetism. Also created a new idea of appearance, titled plum pudding formation.

Rutherford: Fired alpha particles through gold, some rays deviated from center, while others bounced right back. This was because of the positively charged nucleus. He also realized that a lot of the volume of the atom is empty space.

Bohr: Worked in Rutherford's lab, and realized if the charge on the inside was positive, that the negative and positive charges would attract. Created the Bohr model on the assumption that electrons followed specific paths.

Schroedinger: claimed that electrons weren't particles but were in fact waves.

Chadwick: Discovered the neutron by disintegrating atoms through bombardment of  alpha particles. First to create artificial nuclear reaction
Heisenberg: Confirmed both of Bohr and Schroedinger's hypothesis. The electron is indeed a particle, that travels in a wave like motion, which is described by quantum theory.