Polarity

Polarity is a theory in chemistry that tries to explain the unequal sharing or sharing of electrons. These types of sharing electrons define what type of bond a substance is. The bonds are either polar, meaning that the substance has an unequal sharing of electrons, like water, or if it is non-polar, meaning the substance has an almost uniform electric balance, like methane. Also, polarity can also affect the physical characteristics of a substance like melting point, boiling point, freezing point, etc.
The pull between the elements is considered electro negativity, and it is measured and justified by the formation of an electric dipole. What a dipole is is a separation of positive and negative charges into two poles. Furthermore, whichever element has more pull is deemed delta negative, represented by the greek symbol for delta, also with a negative sign. The one with the least pull is deemed delta positive.

Alec W.

The Valence-Shell Electron-Pair Repulsion (VSEPR) Model

At the start of class Mrs. Mandarino stamped the homework pages 18 &19.

Then we reviewed Molecular Geometry, and we started on Molecular Geometry lab.


Molecular geometry is the three dimensional arrangement of the atoms that constitute a molecule. It determines several properites of a substance.

The Valence-Shell Electron-Pair Repulsion (VSEPR) Model

There are basic shape types for molecules.


Linear: In a linear model, atoms are connected in a straight line. The bond angles are set at 180 degree.

Trigonal plannar: The trigonal planar shape are somewhat triangular and in one plane. The bond angles are set at 120 degree.

Tetrahedral: "Tetra" means 4. This is when there are four bonds all on one central atom, with NO extra unshared electron pairs. The bond angles between the electron bonds are set at 109.5 degree.

Trigonal Pyramidal: Pyramidal-shaped molecules have pyramid-like shapes. Requires three dimension in order to fully separate the electrons. The bond angles are set at 107 degree.

Bent: The final basic shape of a molecule is the non-linear shape, also known as bent or angular.


Trigonal Planar: 115 degree


Trigonal Pyramid: 105 degree

Electron Pairs on Central Atom

2/2/0 - Linear
3/3/0 -Trigonal Planar

3/2/1

4/4/0- Tetrahedral
4/3/1

4/2/2

Example:

PCl3

4/3/1 - Trigonal Pyramidal

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HW: Tuesday, Nov.16,2010 = Molecular Geometry Lab (questions), Chemthink & Webassign

Quiz | Review | ions

At the start of class Mrs. Mandarino stamped the homework pg. 11.

Then we reviewed Lewis structure

Example:

H2O

2 x 2e- = 4e-

1 x 8e- = + 8e-

12e- Needed

Minus the total of Valence e- 8e- Total Valence e-

4e- Shared

--------.. ---------- -Has 2 single bonds with equal 4 valence e-
[ H - O - H ] -Has 4 Dots to fill in the ammount of valence
------- `` --------- e- needed.

Next we took the first quiz of our series of quizzes.

Then we went over Covalent ionic bonds.

example:

PO4(3-)

Step 1:

Count the # of atoms total. In the case its 5. 1 P + 4 O = 5.

Step 2:

Take the total # of atoms and times that by 8. This will equal the amount of Valence e- needed

5 x 8 = 40 Valence e- needed

Step 3:

Count the total number of Valence e- for both atoms.

P = 5 valence e- O4 = 24 valence e-

Step 4:

Add the valence e-. [P] 5 + [O4] 24 = 29.

Step 5:

In order to follow the octav rule you must add the 3- e- to the total number of valence e-

29 total Valence e- + 3- = 32 valence eletrons.

Step 6:

Substract the amount of valence e- needed from the amount of total e-

40 valence e- Needed - 32 Valence e- total = 8.

The total amount equals the amount of valence e- shared.

Your math should look something like this.

5 x 8 = 40 Needed

5 + 24 = 29 Total valence e-

29 + 3 = 32 Total valence e- with the 3-

40 - 32 = 8 Shared

The Lewis Structure should look something like this.

------ .. ------

| :O: | 3-

| .. | .. |

| : O - P - O : |

| .. | .. |

| :O: |

| .. |

------ ------|

Ryan G.

Lewis Structures

Today in Chem, Mrs. Mandarino got the party started by showing the class how to draw Lewis Structures. 

And here are some guidelines to drawing Lewis Structures!

Step One: Count the total number of valence electrons in the compound.

Dont forget! If you are finding the structure of an ion, remember to add electrons for a negative charge and subtract electrons for a positive charge.

Step Two: Predict the arrangement of the atoms in the molecule, drawing a line to represent a single bond between each pair of bonded atoms.

• The first atom listed in the formula is usually the central atom.
• Also, remember that Hydrogen can only be bonded to one other atom.

Step Three: Find the number of valence electrons left over after forming the single bond.

• Remember, each single bond you draw counts for two electrons.

Step Four: Place electrons around the outside atoms until each is surrounded by eight electrons. (The octect rule)

• Hydrogen does not follow the octect rule, it will only have two electrons, Boron does not follow the octect rule as well, it will only need 6 electrons.

Step Five: Place any left over electrons around the central atom.

Here's an example of how a Lewis Structure looks for CO2

Kamila W.

Naming Covalent Bonds

Monday, November 8, 2010

Naming Covalent Bonds

Today in class we began to learn how to point out, formulate, and name Covalent Compounds. Today we began class by starting working on our journals, by the end of class we had finished pages 2,3,4,5. Page 6 was our homework for tonight. Page 1 is extra credit.

How to name COVALENT Compounds:
** Write the name of the first element, add appropriate prefixes except for mono
** Write the name of the second element, drop the ending and add -ide.  Add prefiexes indicating the number of atoms.


In naming covalent compounds we use Greek prefixes:

1-mono

2-di

3-tri

4-tetra

5-penta

6-hexa

Then you add the name of the Element

**Exception- The First element for covalent compounds NEVER has a prefix!**

GOT THAT?!

-Patrick W.

Unit Review

Today we began class by stamping pg 14 and going over the answers.
The answers are as followed:

a) magnesium iodine
b) cobalt (II) sulfide
c) copper (I) sulfide
d) Calcium oxide
e) aluminum chloride
f) manganese (IV) oxide
g) Barium Fluoride
h) Sodium Sulfate
i) Iron (II) Carbonate
j) Calcium Phosphide
k) Manganese (IV)Oxide
l) Aluminum Sulfate
m) Mercury (II) Oxide

Rules to remember when naming ions
-write the cation (first part of name)first,then the anion.
-Make sure to drop the ending of the anion(second part of name) and add -ide. ex: Calcium chlorine turns into calcium chloride.
-When given a polyatomic ion look up the name
-When given a transition metal, determine the number of electrons lost and indicate the charge using roman numerals.

ex: FeCl3 (This means we have 1 Fe and 3 Cl)
Look up the charge of Cl, it's -1

Fe
Cl-1
Cl-1 = -3
Cl-1
Because there are 3 Cl's with a -1 charge, there is an overall -3 charge
Next you determine what charge you would need in order for the ion to be neutral.
In this example you need a +3 charge, so the new name becomes: Iron (III) Chloride

Next we reviewed the entire unit as a class, by filling in the Review & Topic outline pages 1 and 2.
Some of the material we reviewed included:
-Whether an element will gain or lose and election and the amount it will gain/lose.
-Completing an orbital diagram and the electron configuration
-How to write the formula of 2 given ions
-How to name the compounds when given the formula
-Naming polyatomic ions
-Naming transition metals in a formula

Homework
Study for the test tomorrow!
Webassigns due Thursday at 11:59pm