1 / 41

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

dex
Télécharger la présentation

Unit 7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related