1. Atoms CHAPTER 4

2. Democritus develops the idea of atoms 460 B.C. he pounded up materials until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible) Were Democritus’ tiny particles really undividable?

3. The Greeks believed… …that all matter was made from 4 elements Aristotle (384-322 BC) Fire is NOT matter! What form of energy is fire? WRONG

4. 1803John Dalton EXPERIMENTAL OBSERVATIONS Combined elements to form compounds Observed that the ratio of elements in a compound was always the same element+ element = compound Magnesium + oxygen = magnesium oxide 10 grams + 6.58 grams = 16.58 grams 1000 grams + 658 grams = 1,658 grams

5. Dalton’s Atomic Theory  Elements are made of tiny particles called ATOMS  All atoms of a element are identical.  And are different from those of any other element  Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply rearranges the way atoms are grouped together.

6. Law of Constant Composition  Atoms of one element can combine with atoms of other elements to form compounds. Ex: H 2 O, CO 2  A given compound always contains the same proportions (by mass and by number) of its elements. Ex: H 2 O, CO 2  This means a given compound always has the same composition, regardless of where it came from. element+ element = compound Magnesium + oxygen = magnesium oxide 10 grams + 6.58 grams = 16.58 grams 1000 grams + 658 grams = 1,658 grams

7. 1803 John Dalton Dalton’s Model of a Atom All matter is made of particles that can’t be divided – ATOMS An ATOM is like a solid sphere Elements are made of 1 type of atom Compounds contain more than 1 kind of atom

8. 1897JJ Thompson EXPERIMENTAL OBSERVATIONS Negatively charged beam attracted to a positive plate (magnet) https://www.youtube.com/watch?v=GzMh4q-2HjM ELECTRON Sealed tube filled with gas

9. JJ THOMSON Evidence / Experiment Negative (-) particles are a part of the atom Since the atom as a whole, is neutral, there must also be positive (+) matter within the atom Description of the model: Chocolate Chip Ice Cream Model Chips are negative particles Ice cream is positive matter 1897

10. 1911Ernest Rutherford oversaw Geiger and Marsden carrying out his famous gold foil experiment. they fired radiation at a very, very thin piece of gold foil (only a few atoms thick). They predicted that the alpha particles would pass right through the foil.

11. 1911Ernest Rutherford Experimental Observations Most of the radiation passed through the foil. However, about 1 in 10,000 particles was deflected.

12. 1911 Ernest Rutherford Theory (model) The radiation was deflected by the NUCLEUS. The Nucleus is positively charged. https://www.youtube.com/w atch?v=5pZj0u_XMbc https://www.youtube.com/w atch?v=5pZj0u_XMbc Predicted result  Actual result  What do the blue circles on the diagram represent?

13. Rutherfords Model of Atoms

14. Empty Space  There is a LOT of empty space is in between the nucleus and the electrons  If the nucleus was a marble on the 50 yard line of a football stadium, the electrons would be in the nosebleed seats…

15. HW: Read Chapter 4.1-4.4 Questions/Problems Pg. 115: #1, 4, 8, 13, 15, 16, 20

16. Subatomic Particles

17. Review: Elements vs. Compounds  Elements can NOT be chemically broken down to a simpler substance, compounds can. (Ex. H 2 O  H 2 + O 2 )  Pure substances can be either elements or compounds. Most materials are MIXTURES of pure substances.  There are only 88 naturally occurring elements, 115 elements that are known.

18. Chemical Formulas  A formula describes how a compound is composed in terms of atoms (how many and which) How many of each atom are in:  Na 2 CO 3  (NH 4 ) 3 PO 4

19. Subatomic Particles  Protons – (p + )  # of proton determines the type of element  Atomic Number = # of Protons  Have a positive charge  Has a mass of 1 a.m.u.  How many protons does Carbon have?  How many protons does Iron have?  How many protons does Ununnilium have?  What element has 35 protons?

20. Subatomic Particles  Neutrons – (n 0 )  Have no (neutral) charge  Have a mass of ~1 a.m.u.  Contributes to the total mass of an atom  Defines the isotope of an atom  Neutrons = Atomic mass – Protons  How many neutrons does Carbon-12 have?  How many neutrons does Carbon-14 have?  How many neutrons does Uranium-238 have?

21. Subatomic Particles  Electrons – (e - )  Have a negative charge  Electrons = Protons (in NEUTRAL atoms)  Gained, lost, or shared in CHEMICAL REACTIONS  Have a mass of 1/1836th of a proton (basically 0!) How many electrons does Carbon have? How many electrons does Potassium have? Which neutral atom has 79 electrons? How many electrons does F - have?

22. Make Up Of Atom  Protons and Neutrons are in the center of the atom.  Electrons are whizzing around on the outside of the atom.  What element (and isotope) is this atom?

23. Isotopes  Isotopes are atoms of an element that have different masses.  Same element = same # protons  Different mass = different # neutrons  Every element has many isotopes – both stable and unstable  The atomic mass on the periodic table is the weighted average of all the stable isotopes of that element.

24. Isotopes  Isotopes of Magnesium 1. Protons: 12, Neutrons: 12, Mass: 24 2. Protons: 12, Neutrons: 12, Mass: 24 3. Protons: 12, Neutrons: 12, Mass: 24 4. Protons: 12, Neutrons: 12, Mass: 24 5. Protons: 12, Neutrons: 12, Mass: 24 6. Protons: 12, Neutrons: 12, Mass: 24 7. Protons: 12, Neutrons: 12, Mass: 24 8. Protons: 12, Neutrons: 12, Mass: 24 9. Protons: 12, Neutrons: 13, Mass: 25 10. Protons: 12, Neutrons: 14, Mass: 26

25. Chart of Nuclides (black = stable, red = unstable)

26. Isotopes  The specific isotope of any element is written with the generic formula Z A X Z = the atomic number A = the mass number (protons + neutrons) X = the elemental symbol  Write the symbol for Magnesium with 13 neutrons.

27. Isotope practice  What is the # of protons, neutrons and electrons for the following isotopes 1. 5 10 B 2. 5 11 B 3. 19 40 K 4. 90 235 Th

28. Isotope Practice  Write the following isotope in the Z A X symbol format. 1. p + = 35, mass # = 126 2. Tungsten, mass # 180 3. Atomic # = 64, n 0 = 91 4. Mass # =60, n 0 = 33

29. Chemical v. Nuclear Reactions  Chemical reactions:  Electrons are involved (exchanged or shared)  Atoms are rearranged into different compounds, but stay as the same atom.  What we will be studying most this year  Nuclear reactions:  Nuclei (protons and neutrons) are involved and changed.  Atoms become different elements by losing or gaining protons.

30. Assignment:  Read 4.5-4.7  Answer: #24, 25, 29-32, 40, 37