Atomic Structure

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#

8. 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?

9. 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

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

12. 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

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

14. 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

15. 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)

16. Atomic Number

17. 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

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

19. Nuclear Symbols

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

21. 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?

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

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

24. Average Atomic Mass • ex.

25. 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

26. 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?

27. 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?

28. Electrons In Atoms

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

30. 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

31. 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

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

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

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

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

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

41. 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

42. Principle Quantum Number

43. Electron Configurations

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

45. Diagonal Rule

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

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

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

49. Practice

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