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Atomic Structure

Atomic Structure. History of the Atom. A. Democritus Particle theory of matter was supported as early as 400 B.C. by the Greek thinker Democritus He was the first person to suggest all matter is composed of “atoma”……atoms. History of the Atom. B. John Dalton (1808)

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Atomic Structure

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  1. Atomic Structure

  2. History of the Atom A. Democritus Particle theory of matter was supported as early as 400 B.C. by the Greek thinker Democritus He was the first person to suggest all matter is composed of “atoma”……atoms

  3. History of the Atom B. John Dalton (1808) Dalton’s Atomic Theory: 1. chemical elements are made of atoms. 2. the atoms of an element are identical in their masses

  4. 3. atoms of different elements have different masses 4. atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on. 5. atoms can be neither created nor destroyed

  5. History of the Atom • What, if any, of Dalton’s ideas are no longer true today? • The atoms of an element are identical in their masses • How do we know this is no longer true? • ISOTOPES

  6. History of the Atom C. J.J. Thomson (1897) Credited with discovering the electron, using a cathode ray tube http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#

  7. History of the Atom D. Millikan (1909) Determined the mass of an electron to be 9.109 × 10-31 kg, using his oil drop experiment How could he measure something so small?

  8. History of the Atom F. Ernest Rutherford (1911) Famous for his gold foil experiment Bombarded a thin gold foil with fast moving alpha particles (pos. charged particles) http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

  9. History of the Atom 2 Major Discoveries Rutherford made: 1. Nucleus is positively charged 2. An atom is mostly empty space

  10. Modern Atomic Theory Atom is composed of 3 subatomic particles: A. Electrons • negatively charged particles that orbit around the outside of the nucleus (electron cloud) • responsible for little or no mass of an atom

  11. responsible for most the volume of an atom • sharing or exchange of electrons between atoms form chemical bonds

  12. Modern Atomic Theory B. Protons • positivelycharged particles foundinsidethenucleus • have a mass of 1 amu (atomic mass unit) • NUMBER OF PROTONS IS UNIQUE TO EACH ELEMENT

  13. Modern Atomic Theory C. Neutrons • found in the nucleus of an atom • has a mass of 1 amu • carries no electrical charge • can vary in number within the same element (Isotopes)

  14. Atomic Number

  15. Modern Atomic Theory Atomic Number • the number of protons in the nucleus • An atom has an overall neutral charge, so what does the atomic number tell us about the number of electrons present? • Atomic number also signifies the number of electrons present in an atom

  16. Nuclear Symbols • Indicates the composition of the nucleus • What 2 particles are found in the nucleus? • protons & neutrons • Written 2 different ways:

  17. Nuclear Symbols

  18. C-12 , C-14 • How can the number of protons, neutrons, and electrons be determined using this notation?

  19. Isotopes & Ions • Isotopes are atoms of elements with different numbers of neutrons • Ex. O-16, O-17, O-18 How many neutrons are present in each isotope?

  20. Ions are atoms with either extra electrons or missing electrons • Ex. Ca +2 Where electrons lost or gained here? • Ex. F- How about here?

  21. Average Atomic Mass • Weighted average of the atomic masses of thenaturally occurring isotopesof an element • Contribution of element = fractional abundance × mass of isotope

  22. Average Atomic Mass • ex.

  23. Average Atomic Mass • ex. Oxygen 16- 15.994915 × .99762 = 15.9568471 • Oxygen 17- 16.999131 × .00038 = .0064596698 • Oxygen 18- 17.999169 × .00200 = .035998338 • Total = 15.9568471 + .0064596698 + .035998338 = • 15.99930511

  24. Section Review • 1. Isotopes of an element have different…. • 2. How many protons, neutrons, and electrons are in a neutral atom of sodium? (Na-23) • 3. Atoms of the same element must…… • 4. Which scientist was the first to conclude through experimentation that atoms have positive charges in their nuclei?

  25. 5. Which idea of John Dalton is no longer considered part of the modern view of atoms? • 6. A neutral atom of aluminum-27 contains: • 7. The atomic number corresponds to an atom’s number of ________ • 8. A scientist has found the following isotope O-19. How many neutrons are present?

  26. Electrons In Atoms

  27. The Bohr Model • Bohr began with the assumption that electrons were orbiting the nucleus, much like the earth orbits the sun

  28. Proposed that: • 1. electrons are confined to specific orbits • 2. electrons have a defined energy state • 3. electrons do not give off energy • 4. electrons will not spiral into the nucleus

  29. Orbital's • Atomic Orbital- the region of space around the nucleus where there is a high probability of finding an electron • Each energy sublevel corresponds to orbital's of different shapes describing where the electron is likely to be found

  30. s sublevel Are spherical in shape • Finding electrons does not depend on direction • Only 1 orbital

  31. p sublevel • Dumbbell shaped • 3 distinct p orbital's • different orientations

  32. d sublevel • Clover leaf in shape • 5 orbital’s

  33. f sublevel • 7 orbital’s • Extremely complex shape

  34. Quantum Numbers • Numbers that specify the properties of atomic orbital’s and their electrons.

  35. Quantum Numbers • Principle Quantum Number (n)- • Have integer values of 1,2,3,etc. • As n increases the electron density is farther away from the nucleus • As n increases the electron has a higher energy and is less tightly bound to the nucleus

  36. Principle Quantum Number

  37. Electron Configurations

  38. Electron Configurations 3 Rules used to determine electron configurations: • Aufbau Principle: electrons occupy lowest energy levels first

  39. Diagonal Rule

  40. Electron Configurations 2. Pauli Exclusion Principle: No 2 electrons can have the same set of 4 quantum numbers

  41. Electron Configurations 3. Hund’s rule: Electrons fill orbital’s 1 at a time beforepairing up

  42. Orbital Diagram • http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter7/animations_center.html#

  43. Practice

  44. Do these on your own: C N Ne Na

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