Monday, November 9th, 2009

Today we saw the topic “Chemical Balancing". Chemical Balancing is a way to balance an equation, and there are 3 methods but today we saw the Trial and error method also known as Inspection method.

We can ask first of all why we need to do it, well we need to follow the rule “matter can’t be created nor destroyed just transformed”.

To make a chemical balance first you need an equation:

Na + Cl → NaCl (It’s not balanced)

Then you need to write the amount of molecules of each element:

Na + Cl2 → NaCl

Na 1 Na 1

Cl 2 Cl 1

If you notice, the amount of Chlorine is not the same and we need to apply the rule of “matter can’t be created nor destroyed just transformed”. So we need to aggregate numbers to balance the equation:

Na + Cl2 → 2NaCl

Na 1 Na 2

Cl 2 Cl 2

Now we balanced Chlorine but now Sodium is not balanced, so we need to aggregate another number:

2Na + Cl2 → 2NaCl

Na 2 Na 2

Cl 2 Cl 2

Now the equation is balanced with the same amount of molecules before and after the arrow.

Michelle Torrero

Friday, November 6th, 2009

Today the class started with awful news: The test is on November 20^th!

So if anyone else was planning to go to the New Moon´s premier you need to come early to school, even if you´re sleepless.

So...

Today´s theme was Chemical formulas and equations

An equation can tell you the elements that you have, the cuantity and, in some cases, the state or compatibility.

A chemical formula is a concize way of expresiing information about the atom that constitute a particular chemical compound.

Every compund that exists has an specific formula.

There are some elements that don´t come alone. They come in pairs:

H2

O2

N2

F2

CL2

BR2

I2

There was another theme today: Types of chemical reactions.

All chemical reactions involve a change in substances and a change in energy. Neither matter or energy is created or destroyed in a chemical reaction, only changed.

There are four types:

SYNTHESIS REACTION
In a synthesis reaction two or more simple substances combine to form a more complex substance.

DECOMPOSITION REACTION
In a decomposition reaction a more complex substance breaks down into simpler parts. Synthesis and decomposition reactions are opposites.

SINGLE REPLACEMENT REACTION
In a single replacement reaction a single uncombined element replaces another in a compound.

DOUBLE REPLACEMENT REACTION
In a double replacement reaction parts of two compounds switch places to form two new compounds.

Erin Alice Gil

The homework was:

Find 3 examples of each type of reaction.

Friday October 30th 2009

On Friday's class we learned about Covalent Bonds.
A Covalent Bond its when atoms share a pair of electrons. The difference between this one and a Ionic Bond its that an ionic bond needs to lose or gain electrons and become positive or negative and covalent bonds just share (both have and use the electrons if they need it).
For example: H= that has 1 valence electron and needs just one to be stable -----> Both can form H2O by a covalent bond.
O= which has 6 valence electrons and needs 2 to be stable
A characteristic of covalent bonds its that are "Polar Molecules", that means that the atoms has more positive charge in one side and negative charge in the other. We can use water (H2O) as an example in this too.




It has positive charge in the Hydrogen side and and negative charge in tho Oxygen side because of the excess of electrons.
(the red one is Oxygen and the whites are Hydrogen.)















When all the class understood this we made an activity outside, we made a covalent and a ionic bond simulating to be atoms (neutrons, protons and electrons).

Laura Carrillo