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John Dalton (1766-1844)

Dalton’s atomic model is one of the fundamentals of physics and chemistry. This theory of atomic composition was partially confirmed by the English chemist John Dalton. He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. This was a revolutionary idea but further experimentation by himself and others. The findings became the basis of Dalton’s Atomic Laws or Model. These laws focus on five basic theories.

Illustration of Daltons theory

''All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements'' - John Dalton



Daltons First Major Step to the Atomic Theory Dalton’s fascination with science included a huge interest in meteorology. Starting in 1793 John kept precise daily weather records for 46 years. The meteorology study here led Dalton to an interest in the gases of the air and their components. This interest of gases led to Dalton’s discovery of the Atomic Theory.

THE PERIODIC TABLE OF ELEMENTS John Dalton was the originator of atomic theory, which provided scientists with new ways of seeing the physical world. Atomic weights and fixed ratios of atoms inside compounds provided researchers and scientists with the knowledge to explore chemical compositions of matter.

Da lton's new information on atomic weights allowed a Russian chemist, Dmitri Mendeleev, to create the periodic table of elements. This table provided the means for discovering new elements, and Dalton also proposed symbols for the elements. The symbols would represent the atom combination in compounds, but these were later changed to abbreviations. Dalton's theory had been accepted at the time, but it opened new questions about atom interactions. The structure and interaction of atoms refined atomic theory.

Until Dalton, the lines between physics and chemistry were almost unnoticeable, but his atomic theory divided the two disciplines. In physics and chemistry, the atom is a cornerstone providing an understanding of matter and force. 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 effect of structure on properties. Dalton's theory did have some inaccuracies, but it did provide the foundation for future generations of scientists.

How did John Dalton figure it out?

His studies on weather led him to develop theories about water vapour and mixed gasses, and in 1801 he came up with Dalton's law of partial pressures: that in a mixture of gases, each component exerts the same pressure as it would if it alone made up the whole volume of the mixture.

What are the strengths and weaknesses of the John Dalton model? Dalton just reached his conclusions by experimentation and examination, which means his theory, may or may not be correct. He was the first to think that everything is made up of matter.

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 * __ Bohr model __**

By Megan Niels Bohr (1885-1962)

- Introduced in 1913 by Niels Bohr

- the model is an improvement on the cubic model discovered in 1902 and is a modification of the Rutherford model introduced by Ernest Rutherford in 1911

- Often referred to as the Rutherford-Bohr model

- Bohr found that radiation is absorbed or emitted when an electron moves from one orbit to another

- Bohr used the laws of motion that were made by Sir Isaac Newton to develop his theory

- in 1913 Niels Bohr by accident stumbled across Balmer's numerology for the hydrogen spectrum, and soon came up with a workable model of the atom

-Angstrom a different scientist, was able to measure the wavelengths of the 4 most easily visible spectra lines of Hydrogen this helped Bohr and Balmer greatly and they discovered a formula to measure the wavelengths of the spectrum lines

- Bohr model of hydrogen

- it is a primitive model of a hydrogen atom

- this atom is depicted as a small positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus like our solar system

- the atom has electrostatic forces providing attraction instead of gravity

- the electrons in the atom can only travel in certain orbits at a specific discrete set of distances from the nucleus with certain energies

- Bohr figured out each orbit is a stationary state, and introduced the concept of stationary orbits

- while in an orbit the electron will not radiate energy

-Bohr discovered the closer to the nucleus the electron is the less energy it needs the farther from the nucleus the more energy

- so Bohr numbered the electrons energy levels, the higher the energy-level number the farther away the electron is from the nucleus and the higher the energy.

- Bohr also discovered that each energy level only holds so many electrons energy level 1 can only hold 2 electrons energy level 2 can only hold 8 and so on

- radiation is absorbed or emitted when an electron moves from one orbit to another.

- Bohr's model was the predominant model until new discoveries in quantum mechanics were made

The Bohr model of Carbon


 * **__Advantages to the__**
 * __Bohr model__**

|| __**Disadvantages to the**__ __**Bohr model**__

|| - Bohr introduced the theory of stationary orbits (greater the distance of the orbit from the nucleus greater will be the energy associated with it) - his model can explain the stability of an atom - it accounts for line spectra || - Only describes atoms with one electron therefore it only apply's to hydrogen - Bohr didn't consider the electrons wave motion but used it as a material particle - Bohr said it was possible to determine both the speed and the location of an electron at the same time and that is practically impossible ||
 * - opened a door to quantum mechanics

- Rutherford conducted an experiment in which he shot relatively large charged particles at a thin gold foil he found that some of the particles went right through but other shot off at odd angles like being deflected from these results he concluded that each atom was mostly empty space but also contained a central mass he also concluded that this central mass must have a positive charge.

- this was the technology Bohr based his model on ^

- Bohr found out that each electron has a ground state(that is the energy level it normally occupies) but the electron can move to a higher-energy, less-stable level or shell, by absorbing energy. This state is called the excited state.

- After the electron is done being excited it can return to its ground state by releasing its energy it has absorbed Shown in diagram below



- sometimes the energy released by electrons occupies the portion of the //electromagnetic spectrum's// which is the range of wavelengths of energy that we detect as visible light, slight variations in the amount of the energy are seen as light of different colors - how spectra color is measured :
 * Violet (380-435nm)
 * Blue(435-500 nm)
 * Cyan (500-520 nm)
 * Green (520-565 nm)
 * Yellow (565- 590 nm)
 * Orange (590-625 nm)
 * Red (625-740 nm)

- there is radiation of all the types in the electromagnetic spectrum can come from the atoms of different element classification of some of the types of radiation by wavelength is:
 * Infrared > 750 nm
 * Visible 400 - 750 nm
 * Ultraviolet 10-400 nm
 * Xrays < 10 nm

- later in the year 1925 a German scientist named Erwin Schrodinger developed on Bohr's and Rutherford's theory.

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Works Cited 1920s, the, and further experiments showed that. "History of atoms." //NoBeliefs.com (Freethinkers)//. N.p., n.d. Web. 15 Oct. 2011. . "Atomic Structure: The Bohr Model - For Dummies ." //How-To Help and Videos - For Dummies//. N.p., n.d. Web. 15 Oct. 2011. . "Atomic theory - Wikipedia, the free encyclopedia." //Wikipedia, the free encyclopedia//. N.p., n.d. Web. 15 Oct. 2011. . "Bohr model - Wikipedia, the free encyclopedia." //Wikipedia, the free encyclopedia//. N.p., n.d. Web. 15 Oct. 2011. . "Chapter 4: Niels Bohr and the Quantum Atom." //Internet FAQ Archives - Online Education - faqs.org//. N.p., n.d. Web. 15 Oct. 2011. . "Development of Bohr's model of the atom - Nsb Notes." //Nsb Notes//. N.p., n.d. Web. 15 Oct. 2011. . Helmenstine, Â Anne Marie, and Ph.D.. "Bohr Model - Bohr Model of the Atom." //Chemistry - Periodic Table, Chemistry Projects, and Chemistry Homework Help//. N.p., n.d. Web. 15 Oct. 2011. . century, the late nineteenth, and most people had accepted Dalton's. "Bohr Model." //UPSCALE Home Page//. N.p., n.d. Web. 15 Oct. 2011. . constant, properly defining the units of the, and R. "Emission Spectrum of Hydrogen." //Purdue University College of Science Welcome//. N.p., n.d. Web. 15 Oct. 2011. . constant, properly defining the units of the, and R. "Emission Spectrum of Hydrogen." //Purdue University College of Science Welcome//. N.p., n.d. Web. 15 Oct. 2011. . constant, properly defining the units of the, and R. "Emission Spectrum of Hydrogen." //Purdue University College of Science Welcome//. N.p., n.d. Web. 15 Oct. 2011. . ohoegh. " Bohr - YouTube ." //YouTube - Broadcast Yourself.//. N.p., n.d. Web. 15 Oct. 2011. .

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 * Science came a long way from the time of Dalton to Bohr. Dalton started off the theory with discovering that elements are in fact atoms, and they cannot be subdivided, created or destroyed.This started off scientific revolution into quantum mechanics. The next model that improved Dalton's theory was the Thomson model in 1897, which was later developed in to the plum pudding model in 1904.The Thomson model generated the discovery of electrons by J.J Thomson. Next came the Rutherford model in 1911. This concluded that there are tiny electrons that surround the nucleus like the planets surround the sun. Then finally in 1913 the Bohr model is introduced.this model is an improvement on the cubic model(1902) the plum pudding model (1904) and the Rutherford model (1911). It depicts the atom as a small positively charged nucleus surrounded by electrons that orbit around like our solar system, but with electrostatic forces instead of gravity. Though the Rutherford was the successor to this model, it did fail. See the Bohr model could only describe atoms with one electron, being Hydrogen. The Bohr model would not work for anything else making it fail. Still it opened up new doors into quantum mechanics.**

Thomson’s Theory By Shaelyn Thomson’s theory was that an atom has a sphere of positive charge with negatively charged electrons inside of it. The positive and the negative charges in an atom are equal in magnitude, which makes the atom electrically neutral. It does not have an overall negative or positive charge. Thomson’s atomic theory was created in 1897. He found that cathode rays could be deflected by an electric field. Cathode rays are streams of electrons in a vacuum tube. Thomson proved that the rays were a negatively charged particle, which later on became known as the electron. Electrons are particles given off by the cathode which is negative electricity. Joseph John Thomson’s effort and research in trying to estimate the number of electrons in an atom, using measurements of the cathode ray, was helped by a student of his named Ernest Rutherford.- Cathode Ray

My Atomic Model - Thomson theory model/ Raisin Bread Model Thomson said that the atom structure is like raisin bread. He just assumed that the basic body of an atom was a sphere shape, having N electrons in a homogeneous jellylike positive charged atom whose total charge cancels the N electrons. The model shows positive and negative charged electrons, which is good. Francis Aston used Thomson’s theory and cathode rays as well to discover something new called isotopes. Isotopes are atoms with electrons that have a different weight.

References " Joseph John Thomson | Chemical Heritage Foundation." //Homepage of the Chemical Heritage Foundation | Chemical Heritage Foundation//. N.p., n.d. Web. 4 Oct. 2011. . "Thomson Model (English)." //Thomson Model (English)//. N.p., n.d. Web. 4 Oct. 2011. . "Thomson's Atomic Theory | Tutorvista.com." //Tutorvista.com - Online Tutoring, Homework Help for Math, Science, English from Best Online Tutor//. N.p., n.d. Web. 4 Oct. 2011. []. **Rutherford Model of the Atom** **By Sonia Orr-McCallum**

In 1906, Ernest Rutherford was experimenting with alpha rays. This experiment was called “Rutherford’s Gold Foil Experiment”. Alpha rays are high speed positively charged particles. Rutherford shot alpha rays at a gold leaf foil target. He then saw that most of the particles went right through the gold foil. Only a little bit of rays bounced back and a very few others were deflected. From this experiment, Rutherford proved that **1)** the atom had a dense but very small positive core, **2)** the electrons were far away from the nucleus, and **3)** the electrons were separated from the nucleus by a lot of empty space.

Then in 1911, Rutherford suggested a new model of the atom. He said that an atom’s positive charges and almost all the mass were concentrated in a tiny atomic nucleus in its center. Also, spinning around the nucleus were the atom’s electrons, kind of looking like planets circling the sun. The negative electrons and the positive nucleus held the atom together.

Some important and improvements on the previous model is that, it’s the first real modern view of the atom and the atom is mostly empty space. These are some negatives about the previous model: does not place electrons in the right energy levels around the nucleus, and does not include neutrons in the nucleus, and also does not relate the valence electric atomic charge. I will show an example of how my model will represent the element carbon: Carbon- **C;** Atomic #- 6; Atomic mass- 12.01; # of protons- 6; # of electrons- 6; Atomic mass - # of protons = # of neutrons…# of neutrons- 6



Time and technology progressed through to the Bohr model, and then Rutherford and Bohr worked together to make a model. They then called that model the Bohr-Rutherford model because they worked on it together. This atom is called the Helium Atom.

• Bortz, Alfred B.. The neutron. New York: Rosen Pub. Group, 2004. Print.

• Johnson, Rebecca L.. Atomic structure. Brookfeild : Twenty-First Century Books, 2008. Print.

• Phillipchuk, Kelly, Bob Kvamme, Camille Hounjet, Ted View, Penny Mohr, Donald Lacy, Heather A. Mace, Kirsten Mah, Igor Nowikow, Joanne Neal, and Lionel Sandner. "Developing Models of Matter." Saskatchewan science 9. Columbus: Pearson, 2011. 153. Print. • Bortz, Alfred B.. The electron. New york: Rosen Pub., 2004. Print.