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3-3: Counting Atoms

3-3: Counting Atoms. Beaker Breaker. What was the name of Rutherford’s experiment? What did Rutherford’s experiment discover? My atomic number is 36..who am I?. Objectives. Explain isotopes Define mass # and atomic #

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3-3: Counting Atoms

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  1. 3-3:Counting Atoms

  2. Beaker Breaker • What was the name of Rutherford’s experiment? • What did Rutherford’s experiment discover? • My atomic number is 36..who am I?

  3. Objectives • Explain isotopes • Define mass # and atomic # • Given the identity of a nuclide, determine its # protons, neutrons & electrons

  4. What is the same for all atoms on an element ? • # protons • Atomic number, Z = # protons in the nucleus of each atom of that element

  5. ISOTOPES • Atoms of the same element that differ in mass • Have the same # protons but different # neutrons

  6. Isotopes (con’t) • Atomic # = # protons • # protons determines the identity of the element • # neutrons determines the isotope of the element • (Another revision to Dalton’s Theory) • Although isotopes differ in mass, they do NOT significantly differ in their chemical properties

  7. Beaker Breaker • The_____________of an element is the number of protons in the nucleus of each atom of that element. • ______________are atoms of the same element that have different masses. 3.________________number is the total number of protons and neutrons in the nucleus of an isotope.

  8. Mass Number • Mass number: total number of protons and neutrons in the nucleus of an isotope # protons (At. #) + # neutrons Mass #

  9. NUCLIDE: particular kind of atom containing a definite number of protons and neutrons • ex. Carbon-14 Mass #, A - total # nucleons (particles that make up the nucleus --> protons and neutrons)

  10. How many neutrons are in carbon-14? If: # protons (At. #) then: 6 + # neutrons + ? Mass # 14

  11. How can you determine the # neutrons in an isotope? Mass ## protons + # neutrons - Atomic #- # protons # neutrons # neutrons

  12. Designating Isotopes • Carbon–14 (name mass #) or…….. • 14Cmass #element symbol. 6 atomic #.

  13. Radium-226 • ID the following: • # protons • # neutrons • # electrons • atomic symbol

  14. Radium-226 • ID the following: • # protons • Atomic # = 88 88 protons • # neutrons • 226-88=138 • # electrons • # protons = # electrons (neutral) 88 electrons • atomic symbol 226Ra • 88

  15. Beaker Breaker • How many protons, electrons, and neutrons are in an atom of bromine-80? • Write the nuclear symbol for carbon-13 • Write the hyphen notation for the element that contains 15 electrons and 15 neutrons.

  16. Homework

  17. Atomic masses are VERY, VERY small…..too small to be measured in grams! We need another way to express “how much”

  18. Electron = 9.10953 x 10-28 g • Proton = 1.67265 x 10-24 g • Neutron = 1.67495 x 10-24g

  19. Scientists use a relative scale to describe atomic mass – Atomic Mass Units • Carbon-12 nuclide is the standard • Carbon-12 = 12 atomic mass units (amu) • The mass of all nuclides is determined by comparing them to carbon-12

  20. What is the value of 1 amu ?? • If 12 amu = 1 carbon-12 atom, then… • 1 amu = 1/12 the mass of a carbon-12 atom • Since H = 1/12 the mass of carbon-12, then.. • H = 1/12 ( 12 amu) = 1 amu • O = 4/3 mass of carbon-12 • = 4/3 (12amu) = 16 amu

  21. If we round…proton = 1 amuneutron = 1 amuelectron = 0 amu proton = 1.007276 amu neutron = 1.008665 amu electron = 0.0005486 amu

  22. Atomic Mass • Sum of subatomic masses in a atom • Carbon-12: • 6 protons = 6 ( 1 amu) = 6 amu • 6 neutrons = 6 ( 1 amu) = 6 amu • 6 electrons = 6 ( 0 amu) = 0 amu 12 amu

  23. Predict the atomic mass of oxygen-16 • 8 protons + 8 neutrons + 8 electrons • = 8 amu + 8 amu + 0 amu • = 16 amu • How does this compare with the atomic mass value on Periodic Table?

  24. Predict the atomic mass of uranium-234 • 92 protons + 142 neutrons + 92 electrons • = 92 amu + 142 amu + 0 amu • = 234 amu • How does this compare with the atomic mass value on Periodic Table? • 238 !!…why is it different?

  25. Average Atomic Mass • Weighted average of the atomic masses of the naturally occurring isotopes of an element

  26. IF 40.% of the students living in Hershey have 2 telephones while 60.% of the students have 4 phones, what is the average # phones in Hershey homes? • (0.40 x 2 phones) + (0.60 x 4 phones) • 3.2 phones • “weighted” average

  27. What is the aver. atomic mass of the chlorine?

  28. Average Atomic Mass = • (isotope mass)(relative abundance[dec]) + (isotope mass)(relative abundance[dec]) • (0.75771)(34.96885amu) + (0.24229)(36.96590amu) • = 35.453 amu

  29. Which isotope of hydrogen is the most abundant…? hydrogen-1 hydrogen-2 hydrogen-3 • Hydrogen-1 (1.0079 = aver. atomic mass on chart)

  30. Complete the following:Beaker Breaker(not in packet)

  31. Complete the following:

  32. Objectives • Define MOLE in terms of Avogadro’s # • Define MOLE in terms of molar mass • Use FLM to convert between grams, moles and # atoms/molecules

  33. Relating MASS to # ATOMS

  34. The Mole (mol) • Amount of substance that contains as many particles as there are atoms in exactly 12 g of carbon-12 (Avogadros #) • Experimentally determined to 6.0221367 x 1023 atoms 6.022 x 1023

  35. “Mole Things” Conversions

  36. How many atoms are in 0.43 moles of copper? • 0.43 mol Cu 6.02 x 1023 atoms Cu = 1 1 mol Cu • 2.6 x 1023 atoms of Cu

  37. How many moles are in 1.4 x 1022 atoms of aluminum? • 1.4 x 1022atoms Al 1 mole Al 1 6.02 x 1023atoms • = 0.023 mol Al

  38. Beaker Breaker • Calculate the number of molecules in 1.058mole of H2O?

  39. Molar Mass • Mass of 1 mole of a pure substance • Numerically equal to the atomic mass but expressed in GRAMS

  40. What is the molar mass of the following: • Potassium ? • 39.098 g (or 39.098 g/mol) Nickel ? • 58.693 g (or 58.693 g/mol)

  41. What is the atomic mass of the following: • Potassium ? • 39.098 amu Nickel ? • 58.693 amu

  42. Gram- Mole Conversions

  43. How many grams are needed to have 0.852 moles gold? • 0.852 mol Au 196.97 g Au 1 1 mol Au = 168 g Au

  44. How many moles are in 55 g of lead? • 55 g Pb 1 mol Pb 1 207.2 g Pb • = 0.26 moles Pb

  45. How many moles are in 86.1 g sodium? • 86.1 g ? mole Na = 1 ? g • 86.1 g 1 mole Na = 1 22.99g • 3.74 moles Na

  46. How many atoms would be in 12.0 grams of carbon-12 ? • If …atomic mass of carbon-12 = 12.0 amu (chart value) • Then…12.0 g C = 1 mole (molar mass) • And since…..1 mole = 6.022 x 1023 atoms • Then…12.0 g carbon contains 6.02 x 1023 C atoms

  47. Beaker Breaker • How many moles are there in 5.04x103atoms of Cu?

  48. Gram #Atoms Conversions

  49. How many atoms are in 54.21 g potassium? • 54.21 g K 1 mole K 6.022 x 1023 atoms K 1 39.098g K 1 mole K • = 8.350 x 1023 atoms K

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