understanding the atom

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  • 1.Chapter IntroductionLesson 1 Discovering Parts of an AtomLesson 2 Protons, Neutrons, and Electrons How Atoms DifferChapter Wrap-Up

2. What are atoms, andwhat are they made of? 3. What do you think?Before you begin, decide if you agree ordisagree with each of these statements.As you view this presentation, see if youchange your mind about any of thestatements. 4. Do you agree or disagree?1. The earliest model of an atom contained only protons and electrons.2. Air fills most of an atom.3. In the present-day model of the atom, the nucleus of the atom is at the center of an electron cloud. 5. Do you agree or disagree?4. All atoms of the same element have the same number of protons.5. Atoms of one element cannot be changed into atoms of another element.6. Ions form when atoms lose or gain electrons. 6. Discovering Part of an Atom What is an atom? How would you describe the size of an atom? How has the atomic model changed over time? 7. Discovering Part of an Atom atom neutron electron electron cloud nucleus proton 8. Early Ideas About MatterDemocritus (460370 BC) believed thatmatter is made of small, solid objectscalled atomos, from which the Englishword atom is derived. 9. Early Ideas About Matter (cont.) Aristotle (384322 BC) did not believethat empty space exists, but insteadbelieved that all matter is made of fire,water, air, and earth. Because Aristotle was so influential,his ideas were accepted andDemocrituss ideas about atoms werenot studied again for more than 2,000years. 10. Daltons Atomic ModelJohn Dalton combined data from his ownscientific research with data from theresearch of other scientists to propose anew atomic theory. 11. The AtomAn atom is the smallest piece of anelement that still represents that element.What is a copper atom? 12. The Atom (cont.) Atoms of different elements are differentsizes, but all are very, very small. You cannot see atoms with just youreyes or even with most microscopes.How would you describe thesize of an atom? 13. The Atom (cont.) The 1981 invention of a high-poweredmicroscope, called a scanning tunnelingmicroscope (STM), enabled scientists tosee individual atoms for the first time. Scientists have learned that atoms arenot the smallest particles of matter. 14. Following his experiments with cathode raytubes, scientist J.J. Thomson concluded thatcathode rays were made of small, negativelycharged particles which he called electrons. 15. ThomsonDiscovering ElectronsAn electron is a particle with one negativecharge (1).electronfrom Greek electron, meansamber, the physical force so calledbecause it first was generated byrubbing amber. Amber is a fossilizedsubstance produced by trees. 16. ThomsonDiscovering Electrons (cont.) Because atoms are neutral, or notelectrically charged, Thomson proposedthat atoms also must contain a positivecharge that balances the negativelycharged electrons. Thomsons proposed atom was a spherewith a positive charge evenly spreadthroughout and negatively chargedelectrons within it. 17. Thomsons model of the atom contained asphere of positive charge with negativelycharged electrons within it. 18. RutherfordDiscoveringthe NucleusScientist Ernest Rutherford set upexperiments to test Thomsons atomicmodel and to learn more about whatatoms contain. 19. Rutherford expected the positive alphaparticles to travel straight through the foilwithout changing direction. 20. Some alpha particles traveled in a straightpath, as expected. But some changeddirection, and some bounced straightback. 21. RutherfordDiscoveringthe Nucleus (cont.)Given the results of the goldfoil experiment, how do youthink an actual atom differsfrom Thomsons model? 22. RutherfordDiscoveringthe Nucleus (cont.) Rutherford concluded that most of anatoms mass and positive charge isconcentrated in a small area in thecenter of the atom called the nucleus. Additional research showed that thepositive charge in the nucleus was madeof positively charged particles calledprotons. 23. RutherfordDiscoveringthe Nucleus (cont.) A proton is an atomic particle that hasone positive charge (1+). Negatively charged electrons move inthe empty space surrounding thenucleus. 24. Rutherfords model contains a small, dense,positive nucleus. Tiny, negatively chargedelectrons travel in empty space around thenucleus. 25. Discovering Neutrons James Chadwick discovered that, inaddition to protons, the nucleus alsocontained neutrons. A neutron is a neutral particle that existsin the nucleus of an atom. 26. Bohrs Atomic Model Niels Bohr proposed that electronsmove in circular orbits, or energy levels,around the nucleus. Electrons closer to the nucleus haveless energy than electrons farther awayfrom the nucleus. 27. Bohrs Atomic Model (cont.) More research showed that, althoughelectrons have specific amounts ofenergy, energy levels are not arrangedin circular orbits. When an electron moves from a higherenergy level to a lower energy level,energy is releasedsometimes asvisible light. 28. In Bohrs model of the atom, electronsmove in circular orbits around the atom. 29. Bohrs Atomic Model (cont.) How did Bohrs model of the atom differ from Rutherfords? 30. The Modern Atomic Model In the modern atomic model, electronsform an electron cloud. An electron cloud is an area aroundan atomic nucleus where an electron ismost likely to be. 31. In this atom, electrons are more likelyto be found closer to the nucleus thanfarther away. 32. The Modern Atomic Model (cont.)How has the model of the atomchanged over time? 33. Quarks Protons and neutrons are made ofsmaller particles called quarks. Scientists theorize that there are sixtypes of quarks: up, down, charm,strange, top, and bottom. Protons are made of two up quarks andone down quark. 34. Quarks (cont.) Neutrons are made of two down quarksand one up quark. The current atomic model might changewith the invention of new technologythat aids the discovery of newinformation. 35. If you were to divide an element intosmaller and smaller pieces, thesmallest piece would be an atom. Atoms are so small that they can beseen only by using very powerfulmicroscopes. 36. Scientists now know that atomscontain a dense, positive nucleussurrounded by an electron cloud. 37. Which term describes a particlewith one negative charge?A. atomB. electronC. nucleusD. proton 38. Whose model of the atomcontained a sphere of positivecharge with negatively chargedelectrons within it?A. DaltonB. DemocritusC. RutherfordD. Thomson 39. Which term refers to an areaaround an atomic nucleus wherean electron is most likely to be?A. electron cloudB. neutronC. nucleusD. proton 40. Do you agree or disagree?1. The earliest model of an atom contained only protons and electrons.2. Air fills most of an atom.3. In the present-day model of the atom, the nucleus of the atom is at the center of an electron cloud. 41. Protons, Neutrons, andElectronsHow Atoms Differ What happens during nuclear decay? How does a neutral atom changewhen its number of protons, electrons,or neutrons changes? 42. Protons, Neutrons, andElectronsHow Atoms Differ atomic number radioactive isotope nuclear decay mass number ion average atomicmass 43. The Parts of the Atom The mass ofelectrons ismuch smallerthan the massof protons orneutrons. Most of themass of anatom is foundin the nucleus. 44. Different ElementsDifferentNumbers of Protons The number of protons in an atom of anelement is the elements atomicnumber. The atomic number is the whole numberlisted with each element on the periodictable. Atoms of different elements containdifferent numbers of protons. 45. Different elements have different atomicnumbers. 46. Different ElementsDifferentNumbers of Protons (cont.) Neutral atoms of different elements alsohave different numbers of electrons. In a neutral atom, the number ofelectrons equals the number of protons;therefore, the number of positivecharges equals the number of negativecharges. 47. Neutrons and Isotopes Atoms of the same element can havedifferent numbers of neutrons. Isotopes are atoms of the sameelement that have different numbers ofneutrons. Most elements have several isotopes. 48. Neutrons and Isotopes (cont.) isotope from Greek isos, means equal; and topos, means place 49. Neutrons and Isotopes (cont.) The mass number of an atom is thesum of the number of protons andneutrons in an atom. Mass number = number of protons + number of neutrons An isotope is often written with theelement name followed by the massnumber. 50. Neutrons and Isotopes (cont.)The average atomicmass of an element isthe average mass of theelements isotopes,weighted according tothe abundance of eachisotope. 51. Radioactivity Marie Curie called elements thatspontaneously emit radiationradioactive. Henri Becquerel and Pierre and MarieCurie discovered that the radiationreleased by uranium was made ofenergy and particles. 52. Radioactivity (cont.) This radiation came from the nuclei ofthe uranium atoms. When uranium releases radiation, itchanges to a different element. 53. Radioactivity (cont.) Nuclear decay is a process that occurswhen an unstable atomic nucleuschanges into another more stablenucleus by emitting radiation. Nuclear decay can produce threedifferent types of radiationalphaparticles, beta particles, and gammarays. 54. An alpha particle is made of two protons andtwo neutrons. When an atom releases analpha particle, its atomic number decreasesby two. 55. When beta decay occurs, a neutron changesinto a proton and a high-energy electroncalled a beta particle. The atomic numberof an atom increases by one because it hasgained a proton. 56. Because gamma rays do not containparticles, the release of gamma rays doesnot change one element into anotherelement. 57. Radioactivity (cont.)What happens duringradioactive decay? 58. Radioactivity (cont.) The energy released by radioactivedecay can be both harmful andbeneficial to humans. Radiation therapy can be beneficial tohumans by destroying harmful cells suchas cancer cells. 59. IonsGaining or Losin