1. History of the Atom Democritus Greek philosopher – 2000 years ago
Model- all matter is made up of small indivisible particle
Called atomos which means indivisible, can’t be cut

2. History of the Atom John Dalton English chemist – 1800’s
Model- the atom is a sphere
Foundation of modern chemistry

3. All elements are composed of atoms are indivisible, indestructible particles
Atoms of the same element are exactly alike
Atoms of different elements are different
Compounds are formed by the joining of atoms of two or more elements

4. History of the Atom J.J. Thomson English scientist - 1897
Discovered a negative particle called the electron

5. History of the Atom J.J. Thomson
Model- atom is a positively charged sphere with negatively charged electrons embedded throughout

6. History of the Atom Ernest Rutherford Model English physicist-1911
Atom is mostly empty space

7. Ernest Rutherford Model
Contains a small positive dense core called the nucleus
Electrons are scattered outside the nucleus

8. History of the Atom Niels Bohr Danish scientist-1913
Model- atom has a positive nucleus and the electrons move outside the nucleus in specific paths called energy levels (1-7)

9. History of the Atom Niels Bohr
The further away the electron is from the nucleus the more energy it has

10. Niels Bohr Electrons can gain or lose energy
Increase in energy when the electron raises or jumps to a higher energy level.
Decrease in energy when the electron falls or drops to a lower energy level.

11. History of the Atom
Erwin Schrodinger
1926
Based on wave mechanics

12. History of the Atom Erwin Schrodinger
Model- electrons move very rapidly in regions of space around the nucleus
This space is called the electron cloud

13. History of the Atom Erwin Schrodinger
You don’t know the exact location of the electron just the most probable location.

14. Structure of the atom Nucleus Located in the center Positive charge
Contains 99.9% of the mass of the atom

15. Structure of the atom Nucleus Protons Positively charged
The number of protons in an atom identifies the type of atom

16. Structure of the atom Nucleus Protons
Has a mass of 1 amu (atomic mass unit)

17. Structure of the atom Nucleus Neutrons Neutral charge Mass of 1 amu
Helps keep the protons from repelling apart

18. Structure of the atom Atomic number Number of protons in the nucleus
Located above the element symbol on the periodic table
examples

19. Structure of the atom Isotope Same number of protons & electrons
Atoms of the same element that has the same number of protons but a different number of neutrons
Same number of protons & electrons
Example: Hydrogen-1. Hydrogen-2, Hydrogen-3

20. Structure of the atom Isotope
A sample of an element contains a mixture of all the isotopes of that element in nature

21. Structure of the atom Mass number
Sum of the protons and neutrons of an atom
Example: Carbon-14, carbon-12
Distinguishes one isotope from another

22. Structure of the atom Mass number
Number of neutron = mass number – atomic number
Examples: Uranium-235, Uranium-238

23. Structure of the atom Atomic mass
Average mass of all the isotopes of that element as they occur in nature

24. Structure of the atom Atomic mass
Round to find the mass number of the most common isotope of that element

25. Structure of the atom Electrons Negative charge Mass of 0.0006 amu
Equal but opposite charge to that of a proton

26. Structure of the atom Electrons
In a neutral, number of electrons equals the number of protons

27. Structure of the atom Electrons
Can determine only the probability of the location of an electron that is in energy levels

28. Structure of the atom Electrons
The amount of energy of an electron determines which energy level it will most likely be found

29. Structure of the atom Electrons
Each energy level can hold a certain number of electrons, the maximum is…

30. Structure of the atom Electrons First energy level – 2 e-
Second energy level –8 e-
Third energy level – 18 e-
Forth energy level – 32 e-

31. Structure of the atom Electrons
The electron arrangement gives an element its chemical properties

32. Structure of the atom Electrons
To be stable, an atom wants 8 electrons in its last energy level & it will bond to achieve this.

33. Electromagnetic force
Forces within the atom
Electromagnetic force
Attraction or repulsion between charged particles

34. Forces within the atom
Electromagnetic force
Same charges repel – Ex – between two protons or two electrons

35. Forces within the atom
Electromagnetic force
Opposite charges attract – ex – between electron to proton

36. Electromagnetic force
Forces within the atom
Electromagnetic force
Keeps the negative electrons orbiting around the positive nucleus

37. Forces within the atom
Strong force
Glues the protons together

38. Forces within the atom
Strong force
Only works at close distances

39. Forces within the atom
Strong force
Greatest force of the four

40. Forces within the atom
Weak force
Responsible for radioactive decay

41. Weak force Forces within the atom
When neutrons change into a proton and an electron

42. Gravity Forces within the atom
Force of attraction between objects of mass

43. Forces within the atom
Gravity
Weakest force of the four

44. Forces within the atom
Gravity
Can work over large distances

45. Nuclear Chemistry
Reactions concerning the nucleus of the atom are considered nuclear chemistry.

46. Nuclear Chemistry
Transmutation - change in the identity of a nucleus as a result of a change in the number of protons.

47. Nuclear Chemistry
Remember: the number of protons determines the identity of the atom. Number of neutrons determine isotopes and number of electrons determine ions (or charge)

48. Nuclear Chemistry Radioactive Decay
Unstable nuclei undergo radioactive decay to become more stable.
Unstable nuclei have greater forces pushing it apart than holding it together.

49. Nuclear Chemistry Radioactive Decay: Applications
Radioactive Dating
Medicine: tracers, radiation therapy
Agriculture: tracing fertilizer, shelf life
Problems: Storage and disposal

50. Nuclear Chemistry
nuclear fission a process in which a very heavy nucleus splits into more-stable nuclei of smaller masses

51. Nuclear Chemistry Nuclear Fission

52. Nuclear Chemistry Nuclear Fission
chain reaction a reaction in which the material that starts the reaction is also one of the products and can start another reaction

53. Nuclear Chemistry Nuclear Fission
Applications:
Controlled: Power Plants and Nuclear Subs
Uncontrolled: “The Bomb”

54. Nuclear Chemistry
nuclear fusion the combining of light-mass nuclei to form a heavier, more stable nucleus

55. Nuclear Chemistry Nuclear Fusion

56. Nuclear Chemistry Nuclear Fusion
Applications:
The SUN!
Maybe, someday, clean energy.
Fusion requires high temperatures to work (like the sun). Scientist are trying to find a way to get a fusion reaction at lower temperatures.