2. CHAPTER 4 – THE ATOM

3. John Dalton’s Atomic Theory (19 th 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

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

5. Rule #5 +

6. 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 10 21 )

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

8. 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/ess entialchemistry/flash/ruther14.swf

9. Composition of Nucleus a)Proton – positive (+1) charged particle of nucleus b)Neutron – neutral (0) charged particle of nucleus

11. Particle Symbol Location Charge Relative Mass Electron e - around nucleus -1 0 Neutron n 0 nucleus 0 1 Proton p + nucleus +1 1

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

13. 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

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

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

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

17. Refresh!!!! I’ve given you 3 numbers: 1)Atomic number 2)Atomic mass 3)Mass number The ones with the word “ATOMIC” is on the periodic table Not on periodic table

18. What’s in a cheeseburger?

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

20. 3 Different Hydrogen Isotopes HYDROGEN – 1 (protium) 1 proton 0 neutrons 1 electron HYDROGEN – 2 (deuterium) HYDROGEN – 3 (tritium) 1 proton 1 neutron 1 electron 1 proton 2 neutrons 1 electron

21. Ways to write isotopes 1) Hyphen notation (2 parts) name of element – # ORsymbol – # ex: carbon-14ORC-14 chlorine-35ORCl-35 hydrogen-3ORH-3 MASS NUMBER

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

23. Ex problem K Potassium 19 39.10 # protons # neutrons # electrons Nuclear symbol Potassium-39 Potassium-40 Potassium-41 19 222021 19 K KK 39 19 41 19 40 19

24. 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

25. amu’s and subatomic particles particleMass (amu) e-p+n0e-p+n0 0.000549 1.007276 1.008665 011011

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

27. Atomic Mass Recall all the hydrogen atoms in the world Hydrogen-1Hydrogen-2Hydrogen-3 Each has their own percent abundance in the world 99%0.2%0.8% Take averages of all the weights of each to find atomic mass atomic mass

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

29. Ex problem: Calculate atomic mass of chlorine. Isotope mass (amu) percent abundance 35 Cl 35 75.770% 37 Cl 37 24.230% Mass contribution = (mass)(abundance)

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

31. Ex problem: Calculate atomic mass of chlorine. Mass contribution = (mass)(abundance) For 35 Cl= (35)(0.75770)= 26.5195 amu For 37 Cl= (37)(0.24230)= 8.9657 amu + 35.4852 amu Matches periodic table for Cl