1. The Atom Atomic Number and Mass Number Isotopes

2. Three fundamental parts of an atom are: protons electrons neutrons Structure of the atom is: protons and neutrons are found in the nucleus electrons are located outside of the nucleus

3. Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds

4. Subatomic Particles There are three subatomic particles that are of interest to chemists. These particles define the nature of atoms and how they are put together. These particles are: Neutrons Protons Electrons

5. Properties of Subatomic Particles ParticleMass, g Relative mass to C-12, amu Charge, Coulombs Unit Charge proton 1.6726 x 10 -24 1.00728 1.67 x 10 -19 +1 electron 9.1096 x 10 -28 0.000549 -1.67 x 10 -19 neutron 1.6749x 10 -24 1.008670 0

6. Subatomic Particles ParticleSymbol Charge Relative Mass Electron e - 1- 0 Proton p + + 1 Neutron n0 1

7. Location of Subatomic Particles 10 -13 cm electrons protons neutrons 10 -8 cm nucleus

8. Representation of Atoms Element Symbol Mass Number Atomic Numbe r

9. Counts the number of protons in an atom

10. Periodic Table Represents physical and chemical behavior of elements Arranges elements by increasing atomic number Repeats similar properties in columns known as chemical families or groups

11. Periodic Table 1 2 3 4 5 6 7 8 11 Na

12. Atomic Number on the Periodic Table 11 Na Atomic Number Symbol

13. All atoms of an element have the same number of protons 11 Na 11 protons Sodium

14. Counting Protons State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons

15. Solution State the number of protons for atoms of each of the following: A. Nitrogen 2) 7 protons B. Sulfur 2) 16 protons C. Barium 3) 56 protons

16. Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons

17. Mass Number Counts the number of protons and neutrons in an atom

18. Atomic Symbols Show the mass number and atomic number Give the symbol of the element mass number 23 Na sodium-23 atomic number 11

19. More Atomic Symbols 163165 O P Zn 81530 8 p + 15 p + 30 p + 8 n16 n35 n 8 e - 15 e - 30 e -

20. Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35 Cl 37 Cl17 chlorine - 35 chlorine - 37

21. Counting Protons, Neutrons & Electrons Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______

22. Solution 12 C 13 C 14 C 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___

23. Protons, Neutrons & Electrons An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 1) 302) 353) 65 B.Number of neutrons in the zinc atom 1) 302) 353) 65 C. What is the mass number of a zinc isotope with 37 neutrons? 1) 372) 653) 67

24. Solution An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 1) 30 B.Number of neutrons in the zinc atom 2) 35 C. What is the mass number of a zinc isotope with 37 neutrons? 3) 67

25. Atomic Symbols Write the atomic symbols for atoms with the following: A. 8 p +, 8 n, 8 e - ___________ B.17p +, 20n, 17e - ___________ C. 47p +, 60 n, 47 e - ___________

26. Solution 16 O A. 8 p +, 8 n, 8 e - 8 B.17p +, 20n, 17e - 37 Cl 17 C. 47p +, 60 n, 47 e - 107 Ag 47

27. Identifying Elements An atom has 14 protons and 20 neutrons. A.Its atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163) 34 C. The element is 1) Si2) Ca3) Se D.Another isotope of this element is 1) 34 X 2) 34 X 3) 36 X 16 14 14

28. Solution An atom has 14 protons and 20 neutrons. A.It has atomic number 1) 14 B. It has a mass number of 3) 34 C. The element is 1) Si D.Another isotope of this element would be 3) 36 X 14

29. Masses of Atoms A scale designed for atoms gives their small atomic masses in atomic mass units (amu) An atom of 12 C was assigned an exact mass of 12.00 amu Relative masses of all other atoms was determined by comparing each to the mass of 12 C An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu.

30. Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number Na 22.99

31. Atomic Mass Using the periodic table, specify the atomic mass of each element (round to the tenths place): A.calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________

32. Solution Using the periodic table, specify the atomic mass of each element (round to the tenths place): A.calcium_40.1 amu _ B. aluminum_27.0 amu _ C. lead_207.2 amu_ D. barium_137.3 amu_ E. iron_55.8 amu__

33. Calculating Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope 1 (%) + mass isotope 2 (%) + … 100 100

34. Atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24 Mg =24.0 amu 78.70% 25 Mg = 25.0 amu 10.13% 26 Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu Mg 24.3

35. Calculating Atomic Mass Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium ?

36. Solution Ga-69 68.9 amu x 60.2 = 41.5 amu for 69 Ga 100 Ga-71 (%/100) 70.9 amu x 39.8 = 28.2 amu for 71 Ga 100 Atomic mass Ga = 69.7 amu

37. Finding An Isotopic Mass A sample of boron consists of 10 B (mass 10.0 amu) and 11 B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

38. Assign X and Y values: X = % 10 B Y = % 11 B Determine Y in terms of X X + Y = 100 Y = 100 - X Solve for X: X (10.0) + (100 - X )(11.0) = 10.8 100 100 Multiply through by 100 10.0 X + 1100 - 11.0X = 1080

39. Collect X terms 10.0 X - 11.0 X = 1080 - 1100 - 1.0 X = -20 X = -20 = 20 % 10 B - 1.0 Y = 100 - X % 11 B = 100 - 20% = 80% 11 B

40. Isotopes of Copper Copper has two isotopes 63 Cu (62.9 amu) and 65 Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass) 1) 30%2) 70%3) 100%

41. Solution 2) 70% Solution 62.9X + 6490 = 64.9X = 6350 -2.0 X = -140 X = 70%

42. Isotopes of chlorine Naturally occurring chlorine consists of 75.53% of the isotope with mass number 35 and 24.47% of the isotope with mass number 37. What is the average atomic mass of naturally occurring chlorine?

43. Solution (0.7553)(34.97 u) = 26.41 u (0.2447)(36.95 u) = 9.04 u Atomic mass of Cl = 35.45 u

45. Where Are the Electrons Located? This question becomes important since the nuclear model of the atom proposed by Rutherford accounted only for the location of the positively charged particles. The location of the electrons is the key to understanding chemistry.