Chapt4 2, 4-3
- 1. Chapter 4 Atoms and their structure
- 2. Idea of the atom Original idea Ancient Greece (400 B.C.) Democritus, Leucippus and Aristotle- Greek philosophers.
- 3. History of the atom Late 1700’s - John Dalton- England. Teacher- summarized results of his experiments and those of others. Elements substances that can’t be broken down In Dalton’s Atomic Theory - combined idea of elements with that of atoms.
- 4. Dalton’s Atomic Theory All matter is made of tiny indivisible particles called atoms. Atoms of the same element are identical, those of different atoms are different. Atoms of different elements combine in whole number ratios to form compounds. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.
- 5. Parts of Atoms J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out. A limited amount of other gases are put in
- 6. Thomson’s Experiment + - Metal Disks Voltage source
- 7. Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment + - Voltage source
- 8. Thomson’s Experiment By adding an electric field he found that the moving pieces were negative + - Voltage source
- 9. Thomson’s Experiment Used many different metals and gases Beam was always the same By the amount it bent he could find the ratio of charge to mass Was the same with every material Same type of piece in every kind of atom
- 10. Thomsom’s Model Found the electron. Couldn’t find positive (for a while). Said the atom was like plum pudding. A bunch of positive stuff, with the electrons able to be removed.
- 11. Rutherford’s experiment When the alpha particles hit a florescent screen, it glows. Here’s what it looked like (pg 72)
- 12. Lead block Uranium Gold Foil Flourescent Screen
- 13. He Expected The alpha particles to pass through without changing direction very much. Because… The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles.
- 14. What he expected
- 15. Because, he thought the mass was evenly distributed in the atom
- 16. Because, he thought the mass was evenly distributed in the atom
- 17. What he got
- 18. Atom is mostly empty. Small dense, positive piece at center. Alpha particles are deflected by it if they get close enough. How he explained it +
- 19. +
- 20. Modern View The atom is mostly empty space. Has two regions. Nucleus - Electron cloud-
- 21. Subatomic particles Electron Proton Neutron Name Symbol Charge Relative mass Actual mass (g) e - p + n 0 -1 +1 0 1/1840 1 1 9.11 x 10 -28 1.67 x 10 -24 1.67 x 10 -24
- 22. Structure of the Atom There are two regions. 1. The nucleus- contains protons and neutrons. Positive charge. Almost all the mass. 2. Electron cloud- most of the volume of an atom (empty space). The region where the electron can be found .
- 23. Counting the Particles Atomic Number Atomic Mass Atomic Number = number of protons (# p) # of protons determines kind of atom. Helps find the atom in the periodic table In neutral atom, atomic number = # of e Atomic mass - avg mass of all isotopes of the atom Mass Number = (rounded atomic mass) # p + # n All the things with mass. NOT on the periodic table
- 24. Symbols if an element has an atomic number of 34 and a mass number of 79 what is the number of protons number of neutrons number of electrons Name
- 25. Isotopes Dalton was wrong. Atoms of the same element not identical, may have different masses. called isotopes – different number of neutrons . Do isotopes of an element have the same number of protons? Electrons?
- 26. Nuclear Symbols Contain the symbol of the element, the mass number and the atomic number. X Mass number Atomic number
- 27. Naming Isotopes Can also be represented as follows: Put the mass number after the name of the element. carbon- 12 carbon -14 uranium-235
- 28. Symbols Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name Na 24 11
- 29. Symbols Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name Br 80 35
- 30. Symbols if an element has 91 protons and 140 neutrons what is the Atomic number Mass number number of electrons Complete symbol Name
- 31. Symbols if an element has 78 electrons and 117 neutrons what is the Atomic number Mass number number of protons Complete symbol Name
- 32. Measuring Atomic Mass Atomic mass – average mass of isotopes in an element Unit is the Atomic Mass Unit (amu) 1 amu = One twelfth the mass of a carbon-12 atom. 1 amu ~ mass of p + and n 0 Mass of isotopes not Exact ( silicon-30 29.974 amu)
- 33. Calculating Atomic Mass Atomic mass: Atomic mass = (m 1 * % 1 ) + (m 2 * % 2 )+ (m n * % n ) m 1 = mass of Isotope 1 % 1 = abundance or percent of isotope 1 MUST BE IN DECIMAL Use for as many isotopes in an element.
- 34. Atomic Mass Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu.
- 35. Atomic Mass Magnesium has three isotopes . 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu , and the rest magnesium 25 with a mass of 25.9826 amu . What is the atomic mass of magnesium?
- 36. Atomic Mass Is not a whole number because it is an average. are the decimal numbers on the periodic table.