CHAPTER 4 – THE ATOM

1. CHAPTER 4 – THE ATOM

2. John Dalton’s Atomic Theory (19th Century) 1) All matter is composed of small particles called atoms 2) All atoms of an element are identical in size, mass, and chemical properties 3) Atoms cannot be created, divided into smaller particles or destroyed 4) Different atoms combine in simple whole number ratios to form compounds 5) In chemical reactions, atoms are separated, combined, or rearranged FALSE FALSE

3. Rule #4 + ELEMENT B ELEMENT A COMPOUND of A and B

4. Rule #5 +

5. What is an atom? • Defn – smallest particle of an element that retains properties of the element How many copper atoms can fit on a penny? 29,000,000,000,000,000,000,000 atoms (29 x 1021)

6. Electron • Discovered by J.J. Thomson (1909) using a cathode ray tube (CRT) • Electron – negative charged particle of matter (-1) - has no relative mass

7. Nucleus • Discovered by Ernest Rutherford (1911) using Gold Foil Experiment • Nucleus – dense, positively charged region in center of atom http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

8. Composition of Nucleus • Proton – positive (+1) charged particle of nucleus • Neutron – neutral (0) charged particle of nucleus

10. Relative Mass ParticleSymbolLocationCharge Proton p+ nucleus +1 1 Neutron n0 nucleus 0 1 Electron e- around nucleus -1 0

11. What makes an atom of one element different from an atom of another element ?

12. Atomic Number • Defn – number of protons in an atom • How is periodic table arranged? by increasing atomic number • How many electrons do atoms have? # electrons = # protons atomic number identifies atoms

13. reading the periodic table Element Hydrogen 1 Atomic number H Symbol 1.008 Atomic mass

14. Mass Number • Defn – total number of protons and neutrons NOT SAME AS ATOMIC MASS!!!!!! Cannot be found on periodic table Hydrogen 1 NO NO NO NO NO!!!! H 1.008

15. Mass Number • Remember this formula to find # neutrons: MAN M – A = N (Mass #) – (Atomic #) = Neutrons

16. Refresh!!!! • I’ve given you 3 numbers: • Atomic number • Atomic mass • Mass number The ones with the word “ATOMIC” is on the periodic table Not on periodic table

17. What’s in a cheeseburger?

18. Isotope • Defn – atoms with same number of protons, but different number of neutrons HYDROGEN - 1 HYDROGEN - 2 HYDROGEN - 3 = protons = neutrons = electrons

19. 3 Different Hydrogen Isotopes HYDROGEN – 1 (protium) HYDROGEN – 2 (deuterium) HYDROGEN – 3 (tritium) 1 proton 0 neutrons 1 electron 1 proton 1 neutron 1 electron 1 proton 2 neutrons 1 electron

20. Ways to write isotopes 1) Hyphen notation (2 parts) name of element – # OR symbol – # ex: carbon-14 OR C-14 chlorine-35 OR Cl-35 hydrogen-3 OR H-3 MASS NUMBER

21. Ways to write isotopes 2) Nuclear symbol (3 parts) 14 6 mass number C element symbol atomic number

22. Ex problem Potassium 19 Potassium-39Potassium-40Potassium-41 K # protons # neutrons # electrons Nuclear symbol 19 19 19 39.10 20 21 22 19 19 19 39 19 40 19 41 19 K K K

23. Mass of individual atoms • Atoms have very very tiny masses to work with (~10-27 kg) • Instead we use a relative mass – atomic mass unit (amu) • Atomic Mass Unit (amu) – 1 amu ≈ mass of 1 proton or 1 neutron

24. amu’s and subatomic particles particle Mass (amu) e- p+ n0 0 1 1 0.000549 1.007276 1.008665

25. Atomic Mass • Defn – weighted average mass of all isotopes of an element • Where can it be found? found on periodic table Potassium 19 K 39.10

26. Ex problem: Calculate atomic mass of chlorine. Isotope mass (amu) percent abundance 35Cl 35 75.770% 37Cl 37 24.230% What do you expect the average to be? About 35 amu Actual = 35.453 amu

27. Which isotope is most abundant?Ar-38, Ar-40, or Ar-41? Argon Ar-40 18 Ar 39.948