1. Atomic Structure History
Chem: Objective 2b-d

2. Activity Research topic using books supplied.
Write down your information found.
Be able to present at the end of class today.
Must have a visual of some kind
Create a visual/act it out/etc.

3. Assignments Purple: John Dalton and his contribution to the atom
Green and Yellow: J.J. Thomson and his contribution to the atom
Pink and Orange: Rutherford and his contribution to the atom
Blue: Explain The Law of Conservation of Matter; Law of Definite Proportions; Law of Multiple Proportions

4. Atom Beginings Democritus Aristotle Greek philosopher
“Atomos” = uncut/indivisible
Did not have evidence
Aristotle
Believed all matter was made up of 4 elements:
Earth, Air, Fire, Water

5. The Atomic Theory John Dalton School teacher
Used experimental evidence – lab work
Dalton proposed a 5 point theory – did not fit all observations
Proposed 3 laws: (at the time were not laws)
Conservation of Mass
Definite Proportions
Multiple Proportions

6. Law Conservation of Mass
Matter can neither be created nor destroyed.

7. Law of Definite Proportions
Ex: (Table Salt) NaCl
The same elements in exactly the same proportions by mass regardless of the size of the sample or sources of the compound.
By mass always consists 39.34% Na; 60.66% Cl.

8. Law of Multiple Proportions
Balanced equations

9. Dalton’s Atomic Theory
All matter is composed of extremely small particles called atoms.
Atoms of given element are identical in size, mass, and other properties
Atoms cannot be subdivided, created, or destroyed
Atoms of different elements combine in simple whole-number ratios to form chemical compounds
In chemical reactions, atoms are combined, separated, or rearranged.

10. Discovery of Electrons
J.J. Thomson
Did experiments using cathode-rays
Opposite attract/Like repel
Discovered atoms were made of small negatively charged particles = electrons
Discovered the atom is NEUTRAL.

11. Cathode Ray Vacuum tube Two metal plates at each end
Cathode plate(-)
Anode plate (+)
Magnets deflected charges(glowing beam)
The beam was made of NEGATIVE charges
ELECTRONS were discovered
Led to the plum pudding model (choc chip cookie)
Explained the atom was NEUTRAL!!

12. Discovery of Nucleus Ernest Rutherford
Shot alpha-particles at thin, gold foil.
Particles deflected
Alpha-particle: 2protons, 2 neutrons, (+) charge
Force of alpha-particles being returned was due to a densely packed bundle of matter with (+) charge
Discovered the NUCLEUS
Dense, (+),
Accounts for mass of atom, not volume

13. Gold-Foil Experiment

14. Gold-Foil Experiment (zoom)

15. Rutherford Model

16. Activity From the Notes Make 5 test questions
Each person make 3 flash cards – don’t show others

17. End of Section 1

18. What is an atom?
Atom: the smallest unit of matter that retains the identity of the substance
3 subatomic particles
Proton (+)
Electrons (-)
Neutral (0) 18

19. Atomic Structure Atoms are composed of 2 regions:
Nucleus: the center of the atom that contains the mass of the atom
Electron cloud: region that surrounds the nucleus that contains most of the space in the atom
Nucleus
Electron
Cloud 19

20. Atomic Structure The Nucleus
The nucleus contains 2 of the 3 subatomic particles:
Protons: positively charged subatomic particles
Neutrons: neutrally charged subatomic particles 20

21. Atomic Structure The Electron Cloud
The 3rd subatomic particle resides outside of the nucleus in the electron cloud
Electron: the subatomic particle with a negative charge and relatively no mass 21

22. Atomic Structure Each element has its own atomic number
Atomic number: the number of protons
Elements are neutral
The number of protons are = the number of electrons
Electric force – holds the atom together
Electric force between protons and electrons
Opposites attract

23. Atomic Number vs. Mass Number
Atomic Number : # of protons
The ATOM’S number
Mass Number: # of protons AND # of neutrons
Sums up the Nucleus

24. Isotope
Atoms with same number of protons, different number of neutrons.
Isotopes vary in mass
Isotopes are distinguished by their # of
neutrons

25. Isotopes Some isotopes are more abundant than others.
Unstable isotopes are called radioisotopes
They emit radiation and decay into other isotopes
Decay until stable
Decay at a fixed rate

26. Isotopes Number of neutrons can be found:
Mass Number (Nucleus) – Atomic Number (Protons)

27. End of Section 2

28. Modern Atomic Theory
The QUANTUM Model

29. Electron Orbital/Configuration
Section 3

30. Atomic Model All models are proposed theories NO Exact model
Bohrs
Quantum model
NO Exact model
Scientist’s experiments
Dalton
Rutherford
Thomson

31. Atoms 2 Regions Nucleus Electron cloud holds what? Protons (+)
Neutrons (0)
Electron cloud
Electrons (-)

32. Bohr Model Niels Bohr proposed this model:
All of the protons and the neutrons
The 3rd ring can hold up to 18 e-
The 1st ring can hold up to 2 e-
The 4th ring and any after can hold up to 32 e-
The 2nd ring can hold up to 8 e-

33. Bohr Model Orbits: paths electrons follow as they circle nucleus
aka: atomic energy levels
Orbitals: 3D region around nucleus that indicates probable location of e-
definite/fixed energy
Closer to nucleus = lower energy
Further from nucleus = higher energy

34. Bohr Model - Orbital Energy
Ladder rung

35. S-Orbital (2e-)
Only ONE “s” orbital per enery level

36. P-Orbitals (6e-)

37. P-Orbitals-Another look:

38. D-Orbitals (10e-)

39. Aufbau Principle
States: e- occupies the lowest energy level that can receive it.
1s=lowest energy level
2s=next lowest
2p… and so on

40. Pauli-exclusion Principle
States: no e- in same atom can have same set of 4 quantum #’s
Opposite spins
No more than two electrons per orbital

41. Pauli-exclusion Principle

42. Hund’s Rule
Orbitals of equal energy each occupied by 1 e- and all e- in singly occupied orbitals must have same spin.
One e- will enter each of the 3 p orbitals in the main energy level before a 2nd e- enters any of them.
Example next slide

43. Energy Level Charts

44. Hund’s Rule
Each orbital must have one e- before another may have a second e-

45. Quantum Model Principal quantum #: Symbol = “n”
Indicates the main energy level occupied by e-
n , e- energy and distance from nucleus
Total # of orbitals existing in a given energy level = n2
EL 1 = 2 orbitals, EL 2 = 4 orbitals, EL 3 = 9 orbitals

46. PAUSE
Configure Your Electrons
WORKSHEET

47. Practice Lithium At#=3 ___ ___ ___ ___ ___
1s 2s 2px 2py 2pz
Lithium At#= ___ ___ ___ ___ ___
Beryllium At#=4 ___ ___ ___ ___ ___
Boron At#= ___ ___ ___ ___ ___
Carbon At#=6 ___ ___ ___ ___ ___

48. Practice Nitrogen At#=7 ___ ___ ___ ___ ___
1s 2s 2px 2py 2pz
Nitrogen At#= ___ ___ ___ ___ ___
1s22s22p3
Oxygen At#= ___ ___ ___ ___ ___
1s22s22p4
Fluorine At#= ___ ___ ___ ___ ___
1s22s22p5
Neon At#= ___ ___ ___ ___ ___
1s22s22p6

49. Practice Phosphorus Sodium Atomic # = 15 1s22s22p63s23p3 Atomic # = 11

50. Animation