April 14 2011

Sup Wes here putting mah name in all the blogs I do from now on.  Learned some atomic theory today, some pretty interesting stuff, I suppose....  So in chemistry, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece (Democritus) and India and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of particles.


I made a little something, something to help explain the different atomic theories.

Scientist and date	Name of model/Idea of theory	Importance/Improvement from last model
Democritus    300 BC	Atom the indivisible particle	Talks about the atom as the smallest particle of matter. Defines the atom as an indivisible particle Explains certain natural occurrences such as the existence of elements
Dalton   1800	The solid sphere model Atoms are seen as solid, indestructible spheres	Explains a lot of chemical properties such as how atoms combine to form molecules Explains chemical change better than the Particle Theory Confirms the basic Laws of Chemistry: Conservation of Mass & definite Proportions
J.J. Thomson  1850	The raisin bun Model Atoms are solid spheres made-up of a solid positive mass (or core) with tiny negative particles embedded in the positive core.l	Infers on the existence of electrons and protons Introduces the concept of the nucleus Infers on the relative nuclear density and atom mass of different atoms
Rutherford  1905	The Planetary Model Gold leaf experiment proves that the nucleus is positive and the electrons are   outside the nucleus.	First real modern view of the atom Explains why the electron spins around the nucleus (Bohr's Contribution)
(Neils Bohr) Bohr- Rutherford  1920	Electrons in Definite energy Levels around  the nucleus Used atomic spectra to prove that electrons are placed in definite orbitals (called shells) around the nucleus.	Explains the role of valence electrons in bonding Relegates the number of valence electrons to the Periods of a periodic table Fully explains ionic and covalent bonding Places electrons in definite energy levels 2 e- in the first 8 e- in the second 8 e- in the third

^ That to easy for you? Then try this out, harder, more complicated , no way your gonna understand this (not really) explanation.

April 4 2011 - Percent Yield and Percent Purity

The percent yield, which serves to measure the effectiveness of a synthetic procedure, is calculated by dividing the actual yield of the product (in grams) by the theoretical yield (in grams).

Percent Yield   =	Actual Yield of Product (in grams) x 100%
	Theoretical (maximum possible) Yield of Product

Lithium chlorate decomposes upon heating to form lithium chloride and oxygen gas according to the equation:

2 LiClO3 ---> 2 LiCl + 3O2

A) Determine the mass of oxygen gas that could be produced by the decomposition of 24.8 g of lithium chlorate.

24.8 g LiClO3 x ( 1 mole LiClO3 / 89 g/mole ) x ( 3 moles O2 / 2 moles LiClO3) X ( 32 g/mole /1 mole O2)=13.2 g

B) In a student experiment, 4.00 g of the gas was produced in a flask containing 24.8 g of the reactant. Determine the percent yield of the student's reaction.

% yield = actual yield / theoretical yield x 100
= 4 g O2 / theoretical yield [ANSWER in A] x100
= 4/13.2 x 100=30.3%

Percent purity is the ratio of the mass of pure substance to the mass of impure substance. 

Percent Purity =	Mass of the Pure Product
	Mass of the Impure Product Obtained

                                                                                                        


Suppose you have 0.500 g of a substance you believe is pure and you determine that it contains 0.300 g of the substance you are looking for.  So your sample is (0.300/0.500) x 100% pure = 60%