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Chemistry LibreTexts

Homework 3

  • Page ID
  • 1.74. 4.62

    Chapter 1

    The atomic mass of chlorine is 35.453 amu. There are two stable isotopes for chlorine. Would either of these isotopes have a mass of 35.453 amu? Why or why not?

    Important things to consider:

    • The atomic mass is the sum of the protons and neutrons.
    • Isotopes vary in the amount of neutrons of the same element.
    • Each isotope will have a different mass number depending upon how many neutrons are present.
    • amu = atomic mass unit
      • unit used for indicating mass on an atomic scale

    Answer: No, because isotopes are variants of an element that differ in the number of neutrons present, but they have the same number of protons (atomic number the same).

    Chapter 4

    Which set of elements would you expect to be different? Explain?

    A. Lithium and Potassium

    B. Carbon and Neon

    C. Sulfur and Oxygen

    D. Aluminum and Thallium

    Important things to consider:

    • The number of valence electrons each element contains.
    • Nonmetal, Metal, Halogen, or noble a gas

    Answer: B. Carbon and Neon, because they belong to different groups. Neon is a noble gas with 8 valence electrons. Carbon is a nonmetal with only 4 valence electrons.

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