chem hw 13

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chem hw 13
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2010-04-12 00:07:58
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homework 13 chapter 12
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  1. Review 12. What happens to the properties of elements across any period of the periodic table?
    Across any period, the properties of elements gradually change. The gradual change is called a periodic trend.
  2. Review 25. Does the periodic table explain the shell model or does the shell model explain the periodic table?
    The shell model is a conceptual model that explains the periodic table.
  3. Review 26. Which electrons are most responsible for the properties of an atom?
    The outer electrons or varience electrons are responsible for the properties of an atom.
  4. Review 27. What is the relationship between the maximum number of electrons each shell can hold and the number of elements in each period of the periodic table?
    The maximum number of electrons each shell can hold is the same as the number of elements in that period.
  5. Exercises 13. Why are the atomic masses listed in the periodic table not whole numbers?
    The atomic masses listed in the periodic table are average numbers that reflect the variety of isotopes that exist for an element.
  6. Exercises 16. What is the approximate mass of a carbon atom in atomic mass units? How about a carbon dioxide molecule?
    From the periodic table we see that a carbon atom has a mass of about 12 amu. The carbon dioxide molecule, CO2 consists of one carbon atom bonded to two oxygen atoms for a total mass of about 44 amu.
  7. Exercises 17. What is the approximate mass of a hydrogen atom in atomic massunits? How about a water molecule?
    From the periodic table we see that a hydrogen atom has a mass of about 1 amu. The water molecule H2O consists of two hydrogen atoms bonded to a central oxygen atom for a total mass of about 18 amu.
  8. Exercises 22. Which of the following diagrams best represents the size of the atomic nucleus relative to the size of the atom:
  9. Exercises 23. A beam of protons and a bem of neutrons of the same energy are both harmful to living tissue. The beam of neutrons, however, is less harmful. Suggest why.
    The neutrons carry no electri charge and thus have a greater liklihood of passing through the tissue.
  10. Esercises 29. What is the function of an atomic model?
    An atomic model predicts the behavior of a system that we cannot _____
  11. Exercise 38. Place the proper number of electrons in each shell.
  12. Exercises 39. Use the shell model to explain why a potassium atom, K, is larger than a sodium atom, Na.
    Both the potassium and sodium atoms are in group 1 of the periodic table. The potassium atom, however, is larger than the sodium atoms because it contains an additional shell of electrons.
  13. Exercise 42. Use the shell model to explain why a lithium atom, Li, is larger than a beryllium atom, Be.
    Both lithium and beryllium are in the second period of the periodic table, which means that they each contain two shells of electrons. The nuclear charge of the lithium atom, however, is not as strong as that of the beryllium atom. The electrons of the lithium atom, therefore, are not drawn in as close to the nucleus as are the electrons of the beryllium atom.
  14. Problem 1. The isotopes lithium-7 has a mass of 7.0160 amu, and the isotope lithium-6 has a mass of 6.0151 amu. Given the information that 92.58% of all lithium atoms found in nature are lithium-7 and 7.42% are lithium-6, show that the atomic mass of lithium is 6.941 amu.
    • Li-6 (6.0151) X (.0742) = .446 amu
    • Li-7 (7.0160) X (.9258) = 6.495 amu

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