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Chapter 3 Notes Atomic Structure

Students will understand the development of atomic theory. Chapter 3 Notes Atomic Structure. I. Early Atomic Constructs. A. What are atoms 1. Democritus - 450 BC Greek, determined matter was composed of ATOMOS A finite piece of matter, considered the smallest peice

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Chapter 3 Notes Atomic Structure

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  1. Students will understand the development of atomic theory Chapter 3 Notes Atomic Structure

  2. I. Early Atomic Constructs • A. What are atoms • 1. Democritus- 450 BC Greek, determined matter was composed of ATOMOS • A finite piece of matter, considered the smallest peice • 2. Modern Definition- Atoms are the smallest piece of “organized” matter of an element having properties of that element • 3. Aristotelian Science- Held that all matter was composed of 4 basic elements… earth/air/fire/water

  3. I. Early Atomic Constructs • A. What are atoms (cont) • 4. Robert Boyle (circa 1660)- Performed quantitative experiments on atoms • a. investigated behavior of gases • Created Boyles Law: The volume of gas is inversely proportional to the pressure (V = 1/P) • As the volume of the gas increases the pressure decreases and as the volume of the gas decreases the pressure increases • 5. Joseph Priestly (circa 1770)- Investigated air • a. determined air to be a vital substance for life • b. determined photosynthesis produced oxygen

  4. I. Early Atomic Constructs • A. What are atoms • 6. Antoine Lavoisler(circa 1790)- Disproved ‘Phlogiston’ theory of George Stahl • a. Conducted quantitative experiments about burning. • b. Names Priestly’s gas to be oxygen • c. Experimentally demonstrated ‘The Law of Conservation of Mass’ • 7. Joseph Proust (circa 1799)- Extended Lavoisler’s concepts

  5. I. Early Atomic Constructs • A. What are atoms • 7. Proust (cont)- • a. Demonstrated the ‘Law of Definite Proportion’ • A compound will have the same proportion of element throughout • Also stated, a given compound will always contain the same proportion of elements by weight • 8. John Dalton (circa 1803)- Builds on Proust’s concepts • a. Derives the ‘Law of Multiple Proprotions’ • 2 elements that form a series of compounds (ex. CO, CO2) combine to give ratios that reduce to a whole number by weight

  6. I. Early Atomic Constructs • A. What are atoms • 8. Dalton (cont)- • b. Determined some of those elements can form more than one compound • c. Expanded on ideas from the Greeks and Boyle to derive the Atomic Theory of Matter • 1. elements are composed of identical atoms • 2. atoms of an element are identical, in all aspects • 3. atoms of different elements differ in mass • 4. atoms combine to form compounds in a definite proportion (this was Proust’s theory) • 5. atoms are not created nor destroyed during a chemical reaction

  7. I. Early Atomic Constructs • A. What are atoms • 9. Joseph Gay-Lussac (circa 1809)- Conducted experiments on gases • a. Determined that gases under controlled temperature and volume have a specific behavior • A given volume of gas reacts to produce a given volume of product • 10. Amedeo Avogadro (circa 1811)- Introduced the concept of molecules

  8. I. Early Atomic Constructs • A. What are atoms • 10. Avogadro (cont) • a. Determined that equal volumes of gas contain equal numbers of atoms/particles/molecules • b. His work was ignored until Einstein (proved N= 6.023 X 1023, Avogadro’s number) • Avogadro’s number is the number of atoms or molecules in a given amount of gas (a mole of gas) • 11. JonsJakob Berzelius (circa 1820)- • a. Established the modern symbol system for elements • b. Discovered Cerium, Selenium, Silicon, and Thorium

  9. I. Early Atomic Constructs • A. What are atoms • 12. Michael Faraday (circa 1839)- • a. Determined atomic structure is related to electricity

  10. I. Early Atomic Constructs • B. Discovering Atomic Structure • 1. General Information • a. Faraday’s discoveries were correct • Atoms contain particles that have electrical charge • 2. Static Electricity • a. Electricity comes from the greek word elekton (the word for amber) • Used the word because when amber was rubbed with a cloth the amber would attract dust

  11. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 2. Static Electricity (cont) • b. Benjamin Franklin studied electricity and determined an object would have 2 charges ( + positive and – negative) • Determined 2 like charges repel each other • Determined 2 opposite charges attract each other • Determined charges can collect on one object and then become attracted to another object • The charge can jump across open spaces (static shock!) • The moving stream of electron charge is called a current

  12. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 3. Cathode Rays and Electrons • a. a cathode tube is an evacuated glass tube • b. on each end of the tube are wires connected to two ends of a battery • c. one end of the tube is connected to the positive end of the batter (anode) and the other end is connected to the negative end of the battery (cathode) • d. inside of the tube is a fluorescent material • e. a stream can be seen inside of the tube

  13. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 3. Cathode Rays and Electrons (cont) • f. since the stream comes from the negative end, it was called a Cathode Ray • The Cathode Ray is responsible for the creation of the TV picture • The ray can move a paddle • The movement proves the electron is a particle • Magnets can deflect the beam, suggesting the particle was negatively charged

  14. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 3. Cathode Rays and Electrons (cont) • g. J.J. Thomson attempted to determine the mass of an electron • Used a specialized Cathode Ray tube with a small hole in it • Used a magnet and a electrically charged plate • The magnet and the plate would ‘bend’ the ray • h. Thomson repeated the experiment using different gases • Used mathematical equations to predict how far each cathode ray would bend (with each new gas)

  15. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 3. Cathode Rays and Electrons (cont) • h. (cont) • Named the beams electrons • Determined the ratio of the electron charge to the mass as 1.76 X 108 coulambs/gram • Thomson concluded: • Electrons are negatively charged • Electrons are particles • Electrons charge ratio to mass is 1.76 X 108 coulambs/gram

  16. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 3. Cathode Rays and Electrons (cont) • i. Robert Millikan- Used oil droplets to determine the charge of an electron • 1.60 X 1o-19 C (Coulamb) • He was able to determine the mass of an electron as well • 9.11 X 10-28 g • The electron is 2000(x) lighter than an atom of Hydrogen

  17. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 4. Radioactivity • a. Henri Bequerel discovered radioactivity • He placed a piece of uranium on unexposed film and it made an image • He helped discover 2 other radioactive elements • Radium and Polonium • b. Radioactivity accompanies fundamental changes in the atom • Chemical properties change as the element gives off radiation • Radiation is the emission of particles/rays from an element

  18. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 4. Radioactivity (cont) • c. Ernest Rutherford studied radioactivity • Using 2 electrically charged plates he was able to see 2 types of radiation • Alpha radiation – Deflected toward the negative plate • Beta radiation – Deflected toward the postivie plate • Gamma radiation – (discovered later) is not deflected in either direction • d. Alpha and Beta rays are particles • Alpha particles have a 2+ charge • Beta particles are considered high speed electrons

  19. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 4. Radioactivity (cont) • e. Gamma radiation acts like X-rays and are not particles • (Go to Types of Radioactive Decay Notes Here!) • 5. The Nuclear Atom • a. An atom has no charge (electrically neutral) • b. Since there are negatively charged particles, there must be positively charged particles • Rutherford was determined to discover where the positively charged particles were located • c. Alpha (radiation) particles were shot at gold foil

  20. I. Early Atomic Constructs • B. Discovering Atomic Structure (cont) • 5. The Nuclear Atom (cont) • d. most passed through without a deflection • e. some were deflected at great angles • The deflection was dependant on the angle of impact with the nucleus of the gold atom (Au) • f. This demonstrated that there was a nucleus to an atom and that the positive charge was within the nucleus

  21. I. Early Atomic Constructs • C. Modern Atomic Theory • 1. General Information • a. atoms have 3 fundamental paricles • Protons– positively charged particle (p+) • Neutrons– particles which carry no charge (n0) • Electrons – negatively charged particles (e-) • 2. The Structure of the Atom • a. The nucleus contains 2 of the particles • Protons and Neutrons • Neutrons have a slightly greater mass than a proton • Protons are 2000 (x) greater in mass than an electron

  22. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 2. The Structure of the Atom (cont) • b. Rutherford visualized the atom as a miniature solar system • The nucleus in the middle • The electrons have different orbitals to circle around the nucleus • The proton’s charge has been simplified to +1 • The electron’s charge has been simplified to -1 • The atomic masses have been abbreviated and expressed as Atomic Mass Units (AMU)

  23. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 3. Atomic Numbers • a. Henry Moseley discovered each atom had a unique positive charge • b. each atom has a different positive charge • Each positive charge is a proton, each atom has a different number of protons • c. The Atomic Number equals the number of protons • d. Since each atom is electrically neutral, the positive charges must equal the negative charges

  24. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 4. Ions • Charged atoms • Atoms can gain or lose electrons • Causes the atom to have a net charge (either positive or negative) • Example : H+ is the hydrogen ion because it lost 1 electron • Ions with more positive (protons) than negative (electrons) charges is positive • Ions with more negative (electrons) than positive (protons) charges is negative • Determining the net charge of the atom is easy… • Charge of ion = [# of p+] – [# of e-] • The loss or gain of an electron doesn’t change the name of the atom (i.e. Hydrogen ion)

  25. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 5. Isotopes • a. Dalton’s second postulate isn’t exactly true… • ‘All atoms of a given element are identical’ • All atoms of a given element do not have the same number of neutrons • Atoms that have the same number of protons but different numbers of neutrons are called Isotopes • Most elements in the first 2 rows have at least 2 isotopes • b. In nature elements are almost always found in a mixture of isotopes • The elements isotopes typically are found in the same percentages

  26. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 5. Isotopes (cont) • c. To identify isotopes, a number is added before the symbol or name, the mass number • The mass number is the sum of the protons and the neutrons in an atom • For example: Oxygen has 8 protons and 8 neutrons (most of the time) or Oxygen has 8 p+ and 7 neutrons (a very small amount of the time), this is an isotope of oxygen • This is why Oxygen's atomic mass is 15.9994, not 16 • For example: an atom with 17 protons and 20 neutrons • We know by the protons it is Chlorine (Cl) and is called Chlorine-37 or 37Cl.

  27. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 6. The Mass of an Atom • a. Always measured in Atomic Mass Units (AMU) • b. Defined as the mass of either a proton or a neutron (loosely defined) • c. The mass of an atom in AMU is approximately the sum of the number of protons and neutrons (not exactly, we just learned about isotopes!) example: Oxygen is approximately 16 AMU (8 p+ and 8 no)

  28. I. Early Atomic Constructs • C. Modern Atomic Theory (cont) • 6. The Mass of an Atom • d. The real AMU for an atom includes the Isotopes by percentage, thus it is called the Average Atomic Mass • Chlorine has two isotopes: • Element Mass # Mass (AMU) Percentage % AMU • Chlorine 35 34.969 75.53 26.412 • Chlorine 37 36.966 24.47 9.0455 • Ave AMU= 35.45 • Carbon 12 12.0 98.89 11.866 • Carbon 13 13.003 1.11 0.144 • Ave AMU= 12.01

  29. I. Early Atomic Constructs • D. Nuclear Reactions • 1. General Information • a. Are the changes in an atom’s nucleus • b. The reactions change the composition of the atom’s nucleus • c. There are 3 types of nuclear reactions • Alpha, Beta, and Gamma rays • d. Radioactivity is the spontaneous emission of radiation from the nucleus of an atom

  30. I. Early Atomic Constructs • D. Nuclear Reactions • 2. Nuclear Stability • a. Most atoms are stable in nature • b. Why are they stable? • The combination of protons and neutrons are nearly equal • There is enough space in the nucleus for the protons to be close together • c. A ‘Strong Nuclear Force’ overcomes the repulsive force of like charges • It is only encountered with subatomic particles

  31. I. Early Atomic Constructs • D. Nuclear Reactions • 2. Nuclear Stability • d. Stable nuclei follow a distinct pattern • Elements 1-20 have equal numbers of protons and neutrons • Atomic #s greater than 83 (can’t have enough neutrons) therefore all are radioactive • e. If too many neutrons, the nucleus is unstable as well, and it will emit Beta radiation • f. Heavy isotopes and light isotopes are also radioactive

  32. I. Early Atomic Constructs • E. Radioactivity • 1. Types of Radioactive Decay (A closer look) • a. Alpha Radiation (Decay) is a stream of Alpha particles • An alpha particle consists of 2 protons and 2 neutrons • Is represented by 42He or 42α • Alpha particles do not penetrate the skin well • b. Beta Radiation (Decay) is a stream of high speed electrons • The electrons come from the nucleus, not the orbitals • Neutrons change into protons and electrons • The protons stays in the nucleus • Is represented by 0-1 e- or 0-1β

  33. I. Early Atomic Constructs • E. Radioactivity (cont) • 1. Types of Radioactive Decay (A closer look) (cont) • b. Beta Radiation is a stream of high speed electrons (cont) • 100 (x) greater penetration of the skin/body then alpha particles • Can damage skin (skin cancer) • c. Gamma radiation is a form of light • Similar to X-rays in behavior • Is represented by 00γ • Accompanies alpha and beta decay

  34. I. Early Atomic Constructs • E. Radioactivity (cont) • 1. Types of Radioactive Decay (A closer look) (cont) • c. Gamma radiation is a form of light (cont) • Has the greatest damage to the body/skin • Lead and concrete barriers can stop gamma radiation • 2. Elemental Radioactive Decay • a. the original nucleus decomposes and becomes a new nucleus (always subtract from the original element) • Ex. 22688Ra  42He + 22286Rn (alpha decay) • Ex. 13153I  0-1β + 13154Xe (beta decay)

  35. I. Early Atomic Constructs

  36. I. Early Atomic Constructs

  37. I. Early Atomic Constructs

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