Dalton’s Atomic Theory by Tiffany, Katelyn, Veronica, Kole

John Dalton (1766-1844) John Dalton was born into a Quaker Family. Born: September 6th, 1766 in Cumberland, England He was an English Meteorologist and then he switched to study of Chemistry and Physics. He proposed the Atomic Theory in 1803 His theory was presented in New System of Chemical Philosophy (1808-1827) This work identified a specific type of atom, therefore rejecting Newton’s theory of chemical affinities. On a side note, he also researched into color blindness. For a more in depth biography of John Dalton, please go to this YouTube Video Link: http://www.youtube.com/watch?v=sDoH5fPTOfo  

Five Main Points of His Atomic Theory Elements are made of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined separated, or rearranged.

Experiments that led Dalton to his theory Dalton used symbols to represent the elements. He imagined atoms to be tiny spheres, thus to draw atoms would be to draw circles. He used patterns within the circles to distinguish the different elements. Using this way to symbolize invisible atoms, he could experiment with their combining properties. He created a “Table of Atomic Weights” and using the information from this table, he placed them in a significant order determined by the weight of the elements, comparing them to hydrogen, the lightest element, which is number one on the table and has the atomic number of 1. Dalton discovered the “Law of Multiple Proportions” and “Law of Definite Proportions”. These state that the weights of elements always combine with one another in ratios of small whole numbers. Dalton experimented with a gas called nitric oxide (NO) and oxygen (O). He reacted them together to produce a third type of gas. The results were determined by the proportions or ratios of the two reacting gasses. 2NO + O -> N2O3 NO + O -> NO2 Dalton carried out experiments like this, using the law of multiple proportions, and completed the table of atomic weights. Key Points: He imagined atoms as tiny spheres He created a table by looking at the patterns within the atom The table he created is now known as the “Table of Atomic Weights” He furthered his experiment by using his information from the table. -He placed each element in a specific order by their weight, comparing them to hydrogen, the lightest element. Because of this he founded “The Law of Multiple Proportions” He continued his experiment by experimenting with nitric oxide and oxygen to see how they reacted with one another. -He observed the ratios and proportions of the two reacting gases He continued these experiments to complete the “Table of Atomic Weights” - Which therefore concluded much of his theory.

Various atoms and molecules as depicted in John Dalton’s A New System of Chemical Philosophy (1808)

How Does John Dalton’s Atomic Theory and Research Fit into the Timeline of Atomic Discovery? -John Dalton’s first discovery was in 1803 -Considered the father of modern theory, Dalton was the first in 2000 years to come up with an atomic theory. He continued his research later in 1803 -During the years 1808-1827, he presented his theory about atoms and their weight in the New System of Chemical Philosophy After his “jump- starting” discovery, many other scientist started research, such as William Thomson in 1824- 1907, who was the first to try to construct a physical model of the atom. Scientists’ research has not “missed a beat” in atomic discovery, since John Dalton.

John Dalton’s Atomic Theory Today Many scientists have expanded upon his theory. Dalton's new information on atomic weights allowed a Russian chemist, Dmitry Mendeleyev, to create the periodic table of elements. Until Dalton, the lines between physics and chemistry was almost unnoticeable, but his atomic theory distinguished and divided the two disciplines. In physics and chemistry, the atom is a cornerstone providing an understanding of matter and force, especially in quantitative analysis. Dalton's theory was the beginning of nuclear energy and fusion research still used today. The theory also provides for the study of the quantitative relationships between substances in chemical reactions, or stoichiometry. It provides for structural theory and arrangements of atoms for influencing properties. Dalton's models eventually turned into the understanding of 3-dimensional qualities of molecules and the affect of structure on properties. Dalton's theory did have some inaccuracies, but it did provide the foundation for future generations of scientists. The parts of his theory that have been proven false are atoms can not be subdivided, created, or destroyed and atoms are identical in size, mass, and other properties. Atoms cannot be subdivided was disproven by the splitting of the atom. Also, The theory that atoms are identical was disproven by the discovery of the neutron. Much of the theory that was proven false was because John Dalton didn’t know certain information about the atom because of the technology he had in the time period.