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Atoms

Atoms. Discovering the Atom. Aristotle vs. Democritus A tomos - not cut Alchemy LaVoisier (late 1700s) Law of Mass conservation. 460 - 370 B.C. 1743 - 1794. Law of Mass Conservation.

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Atoms

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  1. Atoms

  2. Discovering the Atom • Aristotle vs. Democritus • A tomos - not cut • Alchemy • LaVoisier (late 1700s) • Law of Mass conservation 460 - 370 B.C. 1743 - 1794

  3. Law of Mass Conservation • There is no detectable change in the total mass of materials when they react chemically to form new materials • Simply put: Matter is neither created nor destroyed in a chemical reaction

  4. Dalton’s atomic theory • 1. Each element consists of indivisible, minute particles called atoms • 2. All atoms of a given element are identical in mass and properties, and atoms of different elements have different masses and properties • 3. Atoms react with each other in small whole numbers to form compounds

  5. Law of Definite proportions • Joseph Proust 1799, found that for any particular compound the ratio of atoms by mass was always the same regardless of how the compound was made.

  6. Components of the Atom • Protons – positive particles in the nucleus • Neutrons – no charge, found in the nucleus • Electrons – negative particles that orbit the nucleus

  7. Radiation • Becquerel – studied uranium. • At first it appeared to be like X-rays and phosphorescence • But the uranium exposed the photographic paper without needing sunlight

  8. Marie Curie – also in the early 1900s she and her husband Pierre discovered two new radioactive elements, polonium and radium • Radioactivity – describes a materials ability to emit radiation

  9. Types of radiation • α – alpha – positively charged particles of radiation • β – beta – negatively charged particles of radiation (more penetrating than alpha) • γ – gamma – pure energy, extremely good at penetrating materials

  10. Discovering the nucleus • Atoms are far to small to see with a microscope • In the early 1900s scientists began to get an idea of what makes up an atom

  11. Atomic Model – J. J. Thompson • The plum pudding model • Answers these questions: • Something must neutralize the negative charge of the electron • How to combine both charges

  12. Atomic Model - Rutherford Ernest Rutherford • Prove Plum-pudding Model • Design: (1909) • Using positively charged -particles (He nucleus) with high speed • Using ultra-thin gold foil to avoid absorption • Expected result -particles should pass through the gold foil virtually undisturbed

  13. Atomic Theory - Rutherford Experimental Results: • Majority particles pass through without deflection • Some particles deflected • 1 in 20,000 bounced back Conclusion: Atoms must be mostly empty space with a massive, positively charged nucleus.

  14. The diameter of an atom is 100,000 times larger than the nucleus • Electrons orbit in the area between the nucleus and the outside of the atom

  15. Looking at subatomic particles in atoms

  16. Atomic Number • This is the number of protons in an element and how we identify each element • Hydrogen is the first element and has an atomic number of 1 • Helium is the second element and has an atomic number of 2

  17. Mass number • This is the number of nucleons in an atom • Atoms of the same element always have the same atomic number but the mass number may vary

  18. Isotopes • Isotopes are atoms of the same element that have different mass numbers • If the identity of an element is determined by the number of protons what atomic particle must vary in an isotope?

  19. The electron • Nearly 2000 times less massive than the proton or neutron • Electrons orbit around the nucleus and define the size of the atom.

  20. Orbits • If electrons are flying around in the empty space outside the nucleus how can you tell what energy level they have?

  21. Electrons orbit around the nucleus in fixed positions • The Bohr model resembles a solar system with the sun as the nucleus and each planet as electron • A.K.A. the planetary model

  22. Each orbit has a quantum number (n=1, n=2…) The higher the number the farther away the electron is from the nucleus

  23. Is there an n=1.5 orbit? • No, electrons can only be in orbits not between them

  24. How do electrons move between orbits? • They gain energy from light waves

  25. Light • Light is a form of energy that we call electromagnetic radiation

  26. Electrons are able to interact with light, both absorbing and emitting light waves • We can see the emitted light as distinct colors on the visible spectrum

  27. When an electron absorbs light energy it is said to be “excited” and moves to a higher energy level. • An atom with such an electron is in the excited state

  28. When the electron releases the light, the electron falls back to the lowest open level in the atom, we call this relaxing • An atom with no excited electrons is in the ground state.

  29. Light from an atom is not a continuous flow like a rainbow • When atoms are excited by electricity or heat they emit discrete bands of color as they relax again

  30. Since orbits are quantized we know that:

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