1. The Structure of Matter
Atomic Models
Subatomic Particles
Forces Within the Atom

2. Part One: Atomic models past and present

3. Atomic Models Throughout History
Greek (~400 BC)
Dalton (1800)
Thomson (1897)
Rutherford (1908)
Bohr (1913)
Wave Model

4. Greek (~400 BC) Atomos: indivisible
Democritus said the smallest piece of matter was an atom
Theory wasn’t accepted for 2100 years

5. Dalton (1800)
All elements are composed of atoms. Atoms are indivisible and indestructible
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

7. Thomson (1897) Discovered negatively charged particles
The atom was divisible!
Particles discovered are electrons
“Plum Pudding Model”
Atom consists of positively charged material with negative charges spread evenly throughout

8. Here’s JJ!

9. Rutherford (1908) Gold Foil Experiment
Positive particles shot at gold foil occasionally bounced back!
Proposed dense, positively charged center called the nucleus

10. Thomson’s theory

11. Rutherford’s reality

12. Rutherford’s atom

13. Bohr (1913) Electrons move in definite orbits around the nucleus
Places each electron in a specific energy level

14. The Bohr Atom

15. Wave Model Modern model based on wave mechanics
Nucleus is surrounded by electrons
Electrons do not move in orbits
We can determine the probable location of an electron based on the amount of energy the electron has
This probable location is called an orbital

17. Part Two: Subatomic particles

18. Three main subatomic particles
Proton
Neutron
Electron

19. Protons Positively charged Found in nucleus Has a mass of 1 amu
The number of protons determines the identity of the atom
The atomic number tells the number of protons

20. Elements are made of atoms
Hydrogen-1proton
Helium-2 protons
Lithium-3 protons
The number of protons determines the identity
of the element!! (atomic number)

21. What is that other particle found in the nucleus?
It’s a neutron!
Neutrons have no charge
(they’re neutral)
Neutrons have a mass of 1 amu
Proton + neutron = mass number

22. Electrons
Electrons hang out in “orbitals” outside the nucleus of the atom
Electrons have almost no mass
The electron cloud is the majority of the volume of the atom
ELECTRONS ARE NEGATIVELY CHARGED!

23. More electron info!
In a neutral atom, the number of electrons is equal to the number of protons
When an atom gains or loses electrons, it is called an ion.

25. The ionization process
Now I’m a happy ion!
I’m POSITIVE! And my
outer shell is full, without that
troublesome extra electron.

27. This chloride ion has added an electron. It is a NEGATIVE ion!
(note: the inner 2 electrons are not shown)
Now I’m a happy ion!!!

28. Sodium chloride-everybody’s happy!
One lost……
One gained.
(positive ion)
(negative ion)

29. Quick Review:
The three subatomic particles are proton, neutron and electron
Protons are positively charged, electrons are negative, neutrons are neutral
When an electron is lost or gained, the atom becomes an ion.

30. Isotopes
Atoms with the same number of protons but different numbers of neutrons are called isotopes.
Isotopes are designated by the symbol and the mass number:
H-1: 1 proton, no neutrons
H-2: 1 proton, one neutron
H-3: 1 proton, two neutrons

32. It’s the Isotopes!

33. What symbols represent ions?
Elements on the left side of the periodic table will lose electrons to become positive ions
Examples: Ca2+, Na+,Fe3+,Fe2+,Al3+
Elements on the right side of the periodic table will gain electrons to become negative ions
Examples: F-, O2-, P3-, Cl-

34. How big is the nucleus?
If an atom was as big as a football field, the electrons would move over the entire field, while the nucleus would be the size of a lima bean in the middle of the field.

35. If an atom was an elephant, the nucleus would be as big as a flea on the elephant

36. How massive is the nucleus?
Even though the nucleus is VERY small, it is VERY massive. Even though it’s the size of the flea, it would weigh as much as the elephant. And though the electrons take up as much space as the elephant, they would only weigh as much as the flea.

38. End of Part 2

39. Part Three: Forces Within The Atom

40. Forces that govern the behavior of subatomic particles:
Strong
Weak
Electromagnetic
Gravity

41. Strong force Opposes electro- magnetic force of
repulsion between protons
“Glues” protons together to form the nucleus
Greatest of the forces, but has very limited range

42. Weak force
Responsible for radioactive decay in the atom

43. Electromagnetic force
Repels positively charged protons within the nucleus.
Do you remember the force which holds them together so the atom doesn’t explode?
(Yes- strong force!)

44. Strong force overcomes electromagnetic repulsion Electromagnetic force
causes proton repulsion
Strong force
overcomes
electromagnetic
repulsion

45. Gravity Weakest of the forces Force of attraction between all objects
Effect seen easily only for very large objects

46. Uses of the forces

47. THE END