Accelerated Chemistry Chapter 3 Wksht # 1



Acc Chemistry Chapter 3 worksheet # 1 Name KEY KEY KEY

This worksheet is designed to help you practice with counting protons, neutrons, and electrons and also with isotope calculations.

1. Determine the # of protons, neutrons, and electrons in the following elements:

|element |protons |neutrons |electrons |

|Potassium |19 |20 |19 |

|Iron |26 |30 |26 |

|Gold |79 |118 |79 |

2. Complete the following tables:

|Periodic Table Box |37Cl |35Cl |88Sr |90Sr |

|# protons |17 |17 |38 |38 |

|# neutrons |20 |18 |50 |52 |

|# electrons |17 |17 |38 |38 |

|atomic mass number |37 |35 |88 |90 |

|Periodic Table Box | | | | |

| |[pic] |23Na+1 |14N-3 |17O-2 |

|# protons |20 |11 |7 |8 |

|# neutrons |20 |12 |7 |9 |

|# electrons |18 |10 |10 |10 |

|atomic mass number |40 |23 |14 |17 |

3. Calculate the average atomic mass if element X has two isotopes: 28X (mass = 27.98 amu, % abundance = 92.23 %), and 29X (mass = 28.98 amu, % abundance = 7.770 %).

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X = (%)(mass) + (%)(mass)

Average mass = (.9223)(27.98 amu) + (0.07770))(28.98 amu)

Average mass = 28.06 amu

4. Calculate the average atomic mass if Copper has two isotopes: 63Cu (mass = 62.94 amu, % abundance = 69.17%), and 65Cu (mass = 64.93amu, % abundance = 30.83%).

X = (%)(mass) + (%)(mass)

= (0.6917)(62.94 amu) + (0.3083)(64.93 amu)

X = 63.55 amu

5. Explain why the mass of a chlorine atom really isn’t 35.45 amu. The number listed on the periodic table (atomic mass/atomic weight) is an AVERAGE mass. Some atoms weigh 35 amu, some weigh 37. NONE WEIGH 35.45!!!

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