Atomic Structure --Unit Test 7

The Inside Story: The Atom and Radioactivity


True/False

  1. Cathode rays are bent by magnetic or electric fields.

  2. All isotopes of hydrogen have one proton in the nucleus.

  3. A proton and a neutron have approximately the same mass

  4. Alpha particles are attracted to the nuclei of atoms.

  5. All isotopes of any one element exhibit essentially the same chemical properties.

  6. The mass of an atom is mostly in the nucleus.

  7. The mass number is the sum of the number of protons and the number of neutrons in an atom.

  8. All isotopes are radioactive.

  9. An alpha particle is a 2+ helium ion.

  10. Loss of a beta particle produces a product with an atomic number one greater than that of the reactant.

Multiple Choice (Choose the best answer.)

Consider the three statements below in answering questions 1 & 2.

I. Atoms of one element cannot be changed into atoms of another element.
II. Atoms are not created or destroyed in chemical reactions, only rearranged.
III. Atoms contain negative charges embedded in a "dough" of positive charge.

  1. Which statement(s) were part of Dalton's early model of the atom?

    I only

    II only

    III only

    I & II only

    I, II, & III

  2. Based on experiments with cathode ray tubes, Thompson modified Dalton's model of the atom. Which statement(s) represent Thomson's modification?

    I only

    II only

    III only

    I & II only

    I, II, & III

  3. Identify the FALSE statement about Rutherford's "gold foil" experiment.

    Neutral helium atoms were used as "bullets."

    The results were interpreted to mean most of the gold foil was empty space.

    It established the notion of a nuclear atom.

    Alpha particles were repelled by protons in the nucleus.

    Rutherford's model did not explain why electrons orbited the nucleus.

  4. is an isotope of carbon that has a nucleus containing:

    14 neutrons and 6 protons

    6 neutrons and 14 protons

    8 neutrons and 6 protons

    6 neutrons and 8 protons

    None of these.

  5. Which of the following statements about isotopes is FALSE?

    Different isotopes of the same element can have different half-lives.

    Different isotopes of the same element have different numbers of neutrons.

    Bromine atoms with a mass number of 65 contain 30 neutrons.

    The nuclei of all iodine atoms contain 53 protons.

    All isotopes of magnesium contain 24 neutrons.

  6. An element has two naturally occurring isotopes. 80% of the element's atoms have a mass of 17.0 g/mol. 20% of the element's atoms have a mass of 15.0 g/mol. What is the molar mass of the mixture of the isotopes? (All answers in g/mol.)

    15.4

    16.0

    16.6

    32.2

    46.2

  7. Identify the FALSE statement about the half-life of radioactive elements.

    The half-life of a radioactive element is the time it takes 1/2 of the atoms to decay.

    The half-lives of different radioactive elements can range from a fraction of a second to several years.

    Isotopes with short half-lives are very unstable.

    Heating or chemically treating a sample does not change its half-life.

    After 2 half-lives have passed, all of a sample has disintegrated.

  8. The radioactive iodine isotope has a half-life of 8 days. How much will be left of a 1.0 g sample after 24 days?

    1/24 g

    1/8 g

    1/3 g

    1/2 g

    3 g

  9. The equation for a nuclear reaction given below could be completed by using which of the following in the blank?

    + _____ +

  10. Plutonium-238 () undergoes radioactive decay to give as one of the products. The other product and the mass number of the uranium produced are which of the following?

    and

    and

    and

    and

    and

    Problem Solving (Show All Work. Use significant figures)

    1. In his experiments with cathode rays, Thomson found the charge-to-mass ratio for an electron is 1.76 x 108 coulombs/g. In his oil drop experiment, Millikan found the charge is charge of an electron is 1.60 x 10-19 coulomb.

    a) Calculate the mass of a single electron.
    b) Calculate the mass of one mole of electrons.






    2. After 252 days a 24 g sample of scandium-42 decays to only 1.5 g of the isotope. What is the half-life of the scadium?




    3. Radon-222 (222Rn) is an unstable isotope that emits an alpha particle accompanied by a gamma ray. Write the nuclear reaction showing its decay.

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