Atomic Theory

We all know that atoms are the smallest particles of an element and they have the same properties of the element. But thousands of years ago, scientists were experimenting and proposing different theories before the modern atomic theory was proven.

Aristotle proposed the Four Elemenrs Theory, which basically stated that matter was made of earth, air, water, and fire. This theory lasted for 2000 years but was rejected because it couldn't be tested and proven.

Lavoisier stated the first version of the Law of Conservation and Mass and the Law of Definite Proportions.
Proust later proved Lavoidier's Laws to be true.

These are the 5 points of Dalton's Theory:
1) elements are made of atoms, which are tiny particles
2) atoms of the same element are the same
3) atoms in different elements are different and can be distinguished by their weights
4) chemical bonds are formed by the joining of atoms
5) atoms cannot be created, divided into smaller parts, or destroyed

Dalton also found out that water was always made up of 11% hydrogen and 88%oxygen, no matter how many atoms of water there were.

J.J. Thomson's theory was the first to have positive and negative charges. He proved the existence of electrons with a cathode ray tube and measured the charge to mass (e/m) ratio of electrons.

Rutherford thought atoms had a dense, positive center with electrons surrounding the center. He figured out that atoms are mostly empty space.

Niels Bohr proposed that electrons surround the nucleus in different energy levels and that when an electron jumped to the next energy level, the atom released light.

The Modern Atom Theory
The atom is the smallest particle of an element and it has the properties of that element. There are 3 subatomic particles: protons (positive), electrons (negative), and neutrons (no charge).


Here is a detailed timeline of scientists that used their observations and experiments to come up with their own theories of the atom before our modern day atom theory was proposed:
http://www.timelineindex.com/content/view/1228

Enjoy this fun, but educational video!
The Atom Song :)

** Note: Remember our Atomic Theory Timeline assignment is due on Wednesday!**

Percent Yield

Percent Yield is the amount of product obtained in a chemical reaction
It can be determined by the masses used in a reaction and the mole ratios in the balanced equation.

A good website for self study:
http://www.chemcollective.org/stoich/percentyield.php

Example 1:

For the balanced equation shown below, if the reaction of 50.6 grams of Pb(NO₃)₂ produces a 74.2% yield, how many grams of PbO would be produced ?
2Pb(NO₃)₂=>2PbO+4NO₂+O₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of PbO:(mass of PbO)/(mass of Pb(NO₃)₂)*given mass
93.94/310*50.6=15.3
Multiplying the theoretical yield by the percent (and dividing by 100), provides the actual yield.
(theory*%yield)/100=actual yield
(15.3*74.2)/100=11.4

 

Example 2:

For the balanced equation shown below, if the reaction of 57.4 grams of N₂ produces 107 grams of Mg₃N₂, what is the percent yield?
3Mg+N₂=>Mg₃N₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of Mg₃N₂:(mass of Mg₃N₂)/(mass of N₂)*given mass
100.9/28.01*57.4=207
The percent yield is determined as follows:
(actual/theory)*100=%yield
(107/207)*100=51.5%

 

Example 3:

For the balanced equation shown below, if the reaction of 54.9 grams of C₂H₃O₂Cl produces 32.6 grams of CO₂, what is the percent yield?
4C₂H₃O₂Cl+7O₂=>8CO₂+6H₂O+2Cl₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of CO₂:(mass of CO₂)/(mass of C₂H₃O₂Cl)*given mass
352.08/378*54.9=51.1
The percent yield is determined as follows:
(actual/theory)*100=%yield
(32.6/51.1)*100=63.8%

Here is  video about the percent yield found on YouTuBe