Atomic Theory

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Atomic Theory Chapter 4

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Atomic Theory. Chapter 4. Atomic Theory. Science is based off of observations. A Scientific Law is a summary of what is seen in observations. A Scientific Theory is an explanation of why these observations are occurring. - PowerPoint PPT Presentation

Transcript of Atomic Theory

Page 1: Atomic Theory

Atomic Theory

Chapter 4

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Atomic Theory¨ Science is based off of observations.¨ A Scientific Law is a summary of what is

seen in observations. ¨ A Scientific Theory is an explanation of

why these observations are occurring.¨ Both laws and theories are tested by using

them to predict what would happen in certain situations.

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Atomic Theory¨ -Explains why all matter acts as it does

because it is composed of tiny particles called atoms, the basic building blocks of all matter

¨ First theorized by Democritus ~400 BC in ancient Greece.

¨ He thought that matter could NOT be divided infinitely. You had to reach a smallest possible piece. He named this piece an atom, which meant indivisible or can’t be cut.

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More Democritus¨ He and his followers, atomists, said atoms

were small hard particles all made of the same material, but different sizes and shapes.

¨ They were also always moving and capable of joining together.

¨ Since this was ancient Greece, He and the atomists had no way of ever proving his theories and few people believed it.

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Law of Conservation of Mass¨ A chemical reaction does not change the

mass of the matter present.¨ The mass of the reactants is equal to the

mass of the products.¨ This is true even if a different phase of

matter is created.

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Law of definite proportions¨ 1790’s¨ All pure compounds have exactly the same

proportions by mass of elements regardless of size

¨ Water is always 2 hydrogen atoms to every 1 oxygen atom

¨ By mass that is 2 (g) H : 16 (g) O

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Dalton’s Model (1803)¨ people started to accept the idea of atoms

because of his experiments¨ He worked with gases and found that they

acted as though they were made of solid microscopic particles

¨ all elements are made of atoms (indivisible and indestructible)

¨ atoms of the same element are exactly alike¨ atoms of different elements are different¨ compounds are formed by joining two or more

elements

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John Dalton

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Thomson’s Cathode Ray

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Thomson’s Model (1897)

¨ found negative particles could come from neutral elements

¨ atom is made of smaller things (+ & -), and is divisible

¨ successfully separated negative particles (electrons) but could not separate the positive particle (protons)

¨ “plum pudding model” negative particles floating in a positively charged gel like material

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Plum Pudding Model- Thomson

Positive Gel

NegativeParticles

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Sir J. J. Thomson The sir meanshe was knighted

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Rutherford’s Model (1911) ¨ fired protons at a sheet of gold foil most

went through unaffected, some bounced away

¨ there is a small dense area of positive particles at the center of the atom- the nucleus

¨ electrons are scattered near the outside of the atom with mostly empty space between the nucleus and the electrons

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Gold Foil Experiment

Radioactive source

Gold foil

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Rutherford’s Model

nucleus(small dense positive area)

electrons

Empty Space

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Ernest Rutherford

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Bohr Model (1913) ¨ electrons move in definite orbits around the

nucleus ¨ these orbits or energy levels are located at

certain distances from the nucleus

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Bohr’s Model

nucleus

Electrons

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Neils Bohr

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Wave Model (present day) ¨ based on complex math equations¨ orbits are more complex than originally

thought¨ de Broglie stated that electrons

(particles) have wave properties, and he viewed these as standing waves, like those produce when a guitar string is plucked (classical physics.)

¨ Schrodinger assumed that the electron in Hydrogen behaves as a standing wave.

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Wave Model (continued)¨ When Schrodinger’s equation is

analyzed, many solutions are found.

¨ Each solution represents an atomic orbital.¨ An atomic orbital is the most probable

location for finding an electron.

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What is an orbital?¨ It is not a Bohr orbit (not moving in

a circular path.) ¨ How is the electron moving?¨ We don’t know! ¨ There is a fundamental limitation

to just how precisely we can know both the position and momentum of a particle at a given time

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This is kind of how we assume an electron travels

e-

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Heisenberg Uncertainty Principle¨ The more accurately we know the

particle’s position, the less accurately we can know it momentum and vice versa.

¨ We can’t know the exact motion of the electron around the nucleus.

¨ The area that an electron orbits is called an “electron cloud”

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Louis de Broglie Erwin Schrodinger

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Werner Heisenberg