5th hour SG Chem 2
Dr. Finnan
This week in class we dove deeper into chemistry by looking at the history of it. We discovered how chemistry began by learning about the different scientists who had a hand in its foundation. From Empedocles to Democritus to Dalton, we learned about what people believed about the things around us are made of. We also studied Joseph Priestley's discovery of oxygen and Antione Lavoisier's theft by taking the credit. Something I didn't know before was that Napoleon Bonaparte loved science more than war and because of this it led to a competition between Humphry Davy and Joseph-Louis Gay-Lussac. After looking the history of chemistry, we studied the ratios of the masses of elements in a compound and their equations. Then we applied the ratio of the masses of elements in known compounds and made inferences on their compositions. Last week we learned all about atoms, elements, particles, and compounds, but people didn't always know about them.
Empedocles was a Greek philosopher and scientist, he proposed the first theory about what the things around us are made of. He said that all matter was composed of four different elements: fire, air, water, and earth. However, there were many flaws in this because no matter how many times you break something it never ends up as one of those elements. That led to other scientists drawing different conclusions.
Democritus was also Greek, though unlike Empedocles, his new theory for what things are made of was based on reasoning rather than science. He believed that if something, a stone for example, was cut in half again and again until it couldn't be anymore, then you would end up with these microscopic pieces, which he called "atomos", "Atomos" means invisible, the pieces that make up the stone are so small they can't be seen with the naked eye. His idea was dismissed at first, but later became the foundation of what we know today.
Joseph Priestley began to experiment with red mercury calx. He discovered that when it is heated it breaks down into two different substances: liquid mercury and a strange gas. Priestley went further by collecting the gas in jars and studying it. He ran some tests with it, discovering that it made flames burn stronger and allowed a mouse to live longer with it than "normal air." Dephlogisticated air is what Priestley decided to call it, but it didn't stick.
After hearing about Priestley's discovery, Antoine Lavoisier had to perform the experiments himself. He did and decided to rename the strange gas oxygen. Lavoisier went on to discover hydrogen and many other elements as he continued to experiment. He was very technical and weighed everything. This led to Lavoisier establishing the Law of Conservation of Mass: mass cannot be created or destroyed. More and more discoveries were being made on what matter is.
John Dalton put the pieces together and formed a modern atomic theory with four main concepts. These concepts were: 1) All matter is composed of indivisible particles called atoms. 2) All atoms of a given element are identical; atoms of different elements have different properties. 3) Chemical reactions involve the combination of atoms, not the destruction of atoms. 4) When elements react to form compounds, they react in defined, whole-number ratios. Dalton gave structure to the ideas people and scientist were experimenting on.
Humphry Davy and Joseph-Louis Gay-Lussac were rivals, and they were quite opposites. Davy was flamboyant, charismatic, loved leisure, and spent time on many different hobbies. Gay-Lussac was patient, careful, fully devoted to science, and spent time with his family when he wasn't working. Davy discovered sodium and potassium, and after he did so Gay-Lussac and himself raced to discover as much as they could about the new elements. When a strange substance that formed black crystals and could produce a purple vapor was found in seaweed, Gay-Lussac was asked to review and perform the scientists who found it's experiments. He decided to call it "iode," which means purple in Greek, due to its purple vapor. He had no idea that Davy had been told about it and started experimenting as well. Another competition began between them. Gay-Lussac beat Davy to the press by one day with the result that what is called iodine today is an element itself and not composed of chlorine as they suspected at first. There are many different elements, about 116 known today, and they all have their own unique properties.
By looking at the ratio of the masses of a compound, we drew out different particle drawings and equations to represent the compound. One hypothesis was to draw out the atoms with them having the same mass. The second hypothesis was to draw out the atoms with one being heavier than the other based on the ratio. As a class we determined that the second hypothesis was the better option because it made more sense based on our learning from Dalotn and others that every element has different properties and therefore different masses. After this we applied the ratio of masses of compounds to compare unknown compounds with a known compound. These images below show how we calculated the ratios and percentages, and how we determined if the unknown compounds matched up with the known compound, in this case sucrose.
As we learned new things each day in class this week, it all built on each other. Starting with Empedocles and ending with what we know today by studying compounds and their chemical equations. Each scientist provided a stepping stone for the next as they made their discoveries. By looking at what the previous scientists found and experimenting on new ideas and making inferences, we were able to apply what we've learned from these scientists, who gave chemistry its foundation, to learn about different elements and compounds and how they relate.
One question I still have is: what is the Law of Definite Proportions? We didn't have quite enough time to cover it in class, and I'm interested to know how it relates to the comparing of known compounds to unknown compounds.