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Chapter 4

Chapter 4. The Structure of the Atom. Models of Atom through Time. Democritus Aristotle Dalton Thomson model Rutherford model Bohr model Quantum Mechanical model. Democritus (460-370 BC). Matter is composed of atoms in empty space

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Chapter 4

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  1. Chapter 4 The Structure of the Atom

  2. Models of Atom through Time • Democritus • Aristotle • Dalton • Thomson model • Rutherford model • Bohr model • Quantum Mechanical model

  3. Democritus (460-370 BC) • Matter is composed of atoms in empty space • Atoms are solid, homogenous, indestructible, and indivisible • Different kinds of atoms have different sizes and shapes • Size, shape, and movement of atoms determine the properties of matter

  4. Aristotle (384-322 BC) • Empty space cannot exist • Matter is made of earth, fire, air, and water

  5. Dalton’s Model of the Atom • Matter composed of atoms • Said atom is indivisible sphere with uniform density • Theorized atoms of different elements always combine in fixed number ratios to produce specific compounds • Ex: 2H2 + O2 2H2O

  6. Crookes’ Experiment • Cathode ray tube • Disk shaped cathode at narrow end of tube, cross shaped anode at wide end • High voltage applied to electrodes, greenish glow appeared. • Caused by negative particles coming from cathode

  7. Thomson’s Experiment • Used magnets to prove electrons have negative charge when attracted to positively charged plate placed in cathode ray tube (p. 108)

  8. The Electron • Definition: negatively charged subatomic particle • Mass = 9.11 x 10-28 grams • Found around outside of nucleus of atom

  9. Thomson Model • Discovered electron • “Plum Pudding” atomic model • Negative particles stuck in a ball of positive charge

  10. Rutherford Model • Discovered nucleus with gold foil experiment (see next slide) • Most of atom is empty space • Dense positively charged nucleus surrounded by negative electrons

  11. Rutherford’s Gold Foil Experiment

  12. Bohr Model • “Planetary Model” • Electrons travel in orbits around nucleus

  13. Quantum Mechanical Model • Developed by Schrödinger • Used mathematical method to describe the location of electrons in atoms • Address of electron • Mathematically predicts where electron probably is around nucleus • No electron paths, just a fuzzy cloud where electron can be found 90-95% of the time

  14. Rutherford Thompson Quantum Mechanical Bohr All the Models Together

  15. The Proton • Discovered by Ernest Rutherford • Definition: a positively charged subatomic particle • Mass = 1.67 x 10-24 grams • 1836 times larger than mass of electron • Found in nucleus of atom

  16. Neutron • Discovered by James Chadwick (~1935) • subatomic particle having no charge • Mass = same as proton (1.67 x 10-24 grams ) • Found in nucleus of atom

  17. Summary of subatomic particles

  18. Atomic Number • Equals number of protons and electrons in atom for neutral atom • Ex: 3Li = 3 protons ; 3 electrons

  19. Mass Number • Total # of protons and neutrons in atom’s nucleus • Ex: Li: mass # of 7: has 3 protons, 4 neutrons • Is an average of all the isotopes masses.

  20. Writing Convention • Atomic # as subscript to left of symbol • Mass # as superscript to left of symbol • Ex: 1939K

  21. Isotopes • Definition: atoms of the same element that contain different numbers of neutrons, so then have different atomic masses (aka mass #) • Ex: 36Li (lithium-6, Li-6) 37Li (lithium-7, Li-7)

  22. Complete the table for the following isotopes. Examples of isotopes

  23. Complete the table, assuming that each atom is neutral. More Examples of Isotopes

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