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

3. Part One: Atomic models past and present

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

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

6. Dalton (1800) All elements are composed of atoms. Atoms are indivisible and indestructible All elements are composed of atoms. Atoms are indivisible and indestructible Atoms of the same element are exactly alike Atoms of the same element are exactly alike Atoms of different elements are different Atoms of different elements are different Compounds are formed by the joining of atoms of two or more elements Compounds are formed by the joining of atoms of two or more elements

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

9. Here’s JJ!

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

11. Thomson’s theory

12. Rutherford’s reality

13. Rutherford’s atom

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

15. The Bohr Atom

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

18. Part Two: Subatomic particles

19. Three main subatomic particles Proton Neutron Electron

20. 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

21. 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)

22. 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

23. 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!

24. 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.

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

28. 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!!!

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

30. 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.

31. 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

33. It’s the Isotopes!

34. What symbols represent ions?  Elements on the left side of the periodic table will lose electrons to become positive ions –Examples: Ca 2+, Na +,Fe 3+,Fe 2+,Al 3+  Elements on the right side of the periodic table will gain electrons to become negative ions –Examples: F -, O 2-, P 3-, Cl -

35. 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.

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

37. 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.

40. Part Three: Forces Within The Atom

41. Forces that govern the behavior of subatomic particles: SStrong WWeak EElectromagnetic GGravity

42. 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

43. Weak force RResponsible for radioactive decay in the atom

44. 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!)

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

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