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Unit 7

Unit 7. Atomic Structure. Objectives. By the end of the unit, you will be able to: Trace the development of the atomic theory State the laws of conservation of mass, definite proportions, and multiple proportions List the points of Daltons hypothesis

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Unit 7

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  1. Unit 7 Atomic Structure

  2. Objectives • By the end of the unit, you will be able to: • Trace the development of the atomic theory • State the laws of conservation of mass, definite proportions, and multiple proportions • List the points of Daltons hypothesis • Explain the significance of the work of Thompson, Rutherford, and Millikan • Differentiate among atomic and subatomic particles

  3. Objectives continued… • Define isotope, nucleon, nuclide, radioactivity, nuclear force, nucleons, antiparticle, spectrum, spectroscopy, and photoelectric effect • State Planck's hypothesis as it relates to atomic theory • Calculate average atomic mass

  4. Early Atomic Theory • Democritus – Greek philosopher 400 B.C. • Said all matter is made of two things, empty space and small particles called “atoms” • “Atom” comes from the Greek word atomos, which means invisible • He is credited with proposing the first atomic theory • This theory was not accepted at first because of the teachings of Aristotle

  5. Early Atomic Theory • Aristotle • Believed that matter was continuous (not made up of smaller particles) • He called the continuous substance Hyle • His teachings were accepted until the 17th century • His teachings were questioned by more modern scientists, like Isaac Newton and Robert Boyle – they published articles supporting atomic nature of matter, but had no proof

  6. Early Atomic Theory • Joseph Proust • Law of definite proportions – elements in substances always combine in definite whole-number proportions by mass • John Dalton – 1800’s • Came up with the law of conservation of mass • Law of multiple proportions – the ratio of masses of one element that combine with a constant amount of another element can be expressed in small whole numbers

  7. Daltons Atomic Theory • Has four postulates • All matter is composed of atoms • All atoms of the same element are identical • Atoms of different elements are not identical • Atoms combine in simple ratios to form compounds

  8. Early research on atomic particles • Thomson • Used cathode rays to discover electrons • Later he discovered the proton • Millikan • Used an oil drop experiment to find the charge on one electron • With this information, it was possible to determine the mass of one electron • 1/1837 of the mass of a hydrogen atom • Rutherford • Discovered neutrons

  9. Thomson’s Cathode ray experiment its

  10. Millikan’s Oil Drop Experiment • Apparatus

  11. Isotopes • Isotopes – atoms of the same element that differ in mass • Have the same number of protons, but a different number of neutrons • Hydrogen vs. Deuterium

  12. Atomic Number • Atomic Number – the atomic number (Z) of an element equals the number of protons in the nucleus • Determines the identity of the element

  13. The atomic nucleus • The particles that make up the atomic nucleus are the nucleons • These are protons and neutrons • The total number of nucleons of an atom is its mass number (A) • The number of neutrons = A - Z

  14. Periodic table

  15. The Nucleus • Rutherford developed experiments that showed that the atom has a central positive nucleus surrounded by electrons • Gold foil experiment • Showed that the atom consists mostly of empty space

  16. Gold foil experiment

  17. Gold foil experiment

  18. Gold foil experiment • An up-close view of the deflections

  19. Gold foil experiment • One more example…

  20. Nuclear Structure • Nuclear Force – force that holds protons and neutrons together • Atoms are made up of subatomic particles

  21. Subatomic Particles • Leptons - True elementary particles • Electrons • Neutrino • Muon • tau • Hadrons – made of smaller particles • Neutrons • Protons

  22. Antiparticles • For every particle, a mirror-image particle called an antiparticle exists • Antielectron is called a positron

  23. The Leptons • Electrons • Neutrino – neutral particle that is essentially massless • Muon and Tau – both more massive than electrons

  24. The Hadrons • Made up of Quarks (smaller particles) • There are six colors (kinds) of quarks- Up, down, charmed, strange, top, and bottom • Quarks are held together by exchanging particles called gluons • Two groups, Mesons and Baryons • Mesons are composed of a quark and an antiquark • Baryons are composed of three quarks, each of a different color

  25. Radioactivity • Radioactivity is the phenomenon of rays being produced spontaneously by unstable atomic nuclei

  26. Radiation • Three types • Alpha particles – an alpha particle is a helium nucleus • Beta particle – is an electron • Gamma rays – are high frequency x-rays

  27. Alpha Decay • an alpha particle is a helium nucleus

  28. Alpha Decay

  29. Beta Decay • is an electron

  30. Gamma Radiation • high frequency x-rays

  31. The Rutherford-Bohr Atom • The Rutherford-Bohr model of the atom is called the planetary atomic model. Why?

  32. The Rutherford-Bohr Atom

  33. The Rutherford-Bohr Atom • This model describes electrons in orbit around the nucleus • Bohr developed this theory based on evidence from spectroscopy • Spectroscopy is a method of studying substances that are exposed to some sort of continuous exciting energy

  34. Electromagnetic Energy • Visible light, infrared, ultraviolet, x-rays are all forms of electromagnetic energy • Consists of variation in electric and magnetic fields • Frequency – the number of wave peaks in a unit of time • Hertz (Hz)– the unit for frequency • Wavelength – the physical distance between peaks • Represented by the symbol λ (lambda)

  35. Electromagnetic Energy

  36. Electromagnetic Spectrum

  37. Plank’s Hypothesis • Plank proposed that light was radiated in small packets called quanta or photons

  38. The Hydrogen Atom and Quantum Theory • Electrons absorb or emit only whole numbers of quanta • When an electron absorbs a quantum of energy it moves to a higher energy level. When it releases a quantum of energy it drops back down • The smallest orbit an electron can occupy is its ground state

  39. Atomic Mass • One atomic mass unit, u (or a.m.u.), is defined as 1/12 the mass of a Carbon 12 nuclide • Masses • Electron = 9.10953 x 10-28 g = 0.000549 u • Proton = 1.67265 x 10-24 g = 1.0073 u • Neutron = 1.67495 x 10-24 g = 1.0087 u

  40. Average Atomic Mass • The average atomic mass of an element is used in calculations • The average atomic mass is a weighted average of all of the elements isotopes • Av At. Mass = (%A x mass A) + (%B x mass B) 100 • Assignment: 8-9 page 137 • Due at the end of class

  41. CH 7 Review • Answer questions: • 10 (a-g, j, k), 14-19, 23, 24, 33, 34, 36, 37, 49, 53 • 15 Points • Due Thursday (before exam)

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