So, here are the stuff that I've studied so far...
1. Determining purity (5/12/12)
-Chromatography
2. Elements, Compounds and Mixtures (7/12/12)
-Atoms and Molecules
-Naming compounds
-Fixed compositions of compounds
-Chemical formula of a compound
-Decomposition of compounds
And preparing for a diagnostic test in class:
1. History of the model of the atom (19/12/12)
2. Structure of an atom (19/12/12)
3. Isotopes (21/12/12)
4. Electronic configuration (21/12/12) <--- yep...even on the so called "end of the world" XD
I've also been crazy enough to draw out the whole periodic table by hand and memorize the first few elements. XD (Though I forgot quite a few. :P)
So, I'll fill in on some of the notes I've taken so far. My references are Tan, Y.T, Chen, L.K., Chemistry Matters for GCE 'O' Level, Federal by Marshall Cavendish, 2006 and Briggs, J.G.R., Chemistry Insights, Longman, SIngapore, 2000.
This is roughly the scheme of work that I will be covering during the module:
1. Elements, Compounds and Mixtures
2. Separation techniques
3. Kinetic particle theory - Physical changes
4. Kinetic particle theory - Chemical changes
5. Kinetic particle theory - Rate of changes
6. Nomenclature and Chemical compounds
And so the journey begins...
Determining purity
A PURE substance is made up of only ONE substance and NOT mixed with any other substance.
A MIXTURE is a substance that contains two or more substances that are NOT chemically combined.
e.g. White diamonds are pure carbon, but coloured diamonds are impure as they contain substances other than carbon. (Some advice on choosing jewelry. ;) )
Why is it important to determine the purity of a substance?
It is important as impurities may cause undesired effects, for example, certain medicines may contain harmful impurities that may cause undesired side effects.
Having an impure substance will affect certain properties of the substance as listed below:
Melting point
-The melting point is lower (The more impure the substance, the lower the melting point)
-Melting takes place over a range of temperatures (e.g., it may melt between xºC to yºC.)
Pure solids have FIXED melting points.
Boiling point
-The boiling point is increased (The more impure a substance, the higher the boiling point)
-The liquid will boil over a range of temperatures.
Pure liquids have EXACT and CONSTANT boiling points.
Pressure has its effects on boiling points too!
-The greater the pressure, the higher the boiling point.
-The lesser the pressure, the lower the boiling point.
Chromatography
Chromatography is the technique of using a solvent to separate a mixture into its components.
Paper chromatography is one of the most commonly used methods.
EXPERIMENT TIME!!! (Okay, I didn't do it, but it's an example.)
Separating dyes of food colouring
1. A spot of food coloring is applied to the chromatography paper.
2. The chromatography paper is dipped in ethanol (which is the solvent) and it soaks up the ethanol.
3. The ethanol dissolves the dye. The ethanol continues to travel up the paper, carrying the dyes along.
-Dyes that are very soluble in ethanol will be carried very far up the paper.
-Dyes that are not very soluble in ethanol will not be carried very far up the paper
4. Coloured spots are left in different places on the paper at the end of the experiments.
There's your chromatogram.
There's your chromatogram.
HOWEVER
If there is only one colored spot on the chromatography paper, the substance is pure.
Here's a diagram I drew:
Now, the positions of the solvent front and spot on a chromatogram depends on the duration of the experiment that the chromatography paper was allowed to soak.
BUT
The ratio between the distance travelled by the substance and the distance travelled by the solvent is CONSTANT. We call this ratio...... the Rf value.
Formula for Rf value of substance:
Rf = Dist. travelled by substance
Dist. travelled by Solvent
Elements, Compounds and Mixtures
Some definitions:
Elements
A pure substance that cannot be split up into two or more simpler substances by chemical processes or by electricity.
Elements are made up of tiny particles called atoms. Atoms are the smallest particles of an element that contains the chemical properties of the element. To show an atom of an element, chemists use its chemical symbol as shown in the periodic table (all known elements and their symbols are recorded in the periodic table).
DIFFERENCE BETWEEN ATOMS AND MOLECULES
Atoms are individual particles. Molecules however, are a group of 2 or more atoms chemically joined together. E.g., The chemical symbol of water is H2O, that means that there are 2 hydrogen atoms and one oxygen atom that are chemically combined. (This proves that water is not an element. Neither is air, fire or earth.)
Classification of elements
There are 2 major groups of classification: Metal and Non-metal. Some elements, known as metalloids, have properties of both metals and non-metals. (This will be more detailedly covered later on in the module)Compounds
A compound is a pure substance that contains 2 or more elements that are chemically combined.
E.g., When magnesium burns in oxygen to obtain magnesium oxide: 2Mg(s) + O2(g) --> 2MgO(s)
History of the model of the atom
Here's a timeline of what happened:
1803 - Dalton viewed atoms like small solid balls that cannot be broken. However, in the late 19th Century, scientists began to obtain experimental evidence, which proved that atoms are not like solid balls and that they could be broken.
1897 - J. J. Thomson, and English physicist, did experiments that led to the discovery of the electron. Thomson showed that 1, an electron carries negative charge and; 2, atoms contained electrons.
1903 - Thomson proposed a new model of the atom. He described the atom as a positively charged sphere with electrons pushed into it (something like a cake studded with raisins with the raisins being the electrons).
1910 - This model was soon modified by New Zealand physicist, Ernest Rutherford. He carried out a simple but clever experiment that proved that the atom had a nucleus. In this experiment, Rutherford used small positively charged alpha particles to bombard a thin sheet of gold foil. (Looks something like this:
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