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Sample Quiz: Chemistry Chapter 2

Atoms, Molecules, and Ions — Chemistry: The Central Science, 15th Global Edition in SI Units (Theodore L. Brown, H. Eugene LeMay, Jr., Bruce E. Bursten, Catherine J. Murphy, Patrick M. Woodward, Matthew W. Stoltzfus)

10 questions · 23 points · answer key included

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Multiple Choice

  1. According to Dalton's atomic theory, which of the following statements is correct? (2 PTS)
    1. Atoms are divisible into smaller, fundamental particles.
    2. All atoms of a given element are identical, but atoms of one element differ from atoms of other elements.
    3. Atoms of different elements can have identical properties.
    4. Compounds are formed when atoms of the same element combine in varying ratios.
  2. Which of the following compounds would you expect to be ionic? (2 PTS)
    1. N2O
    2. Na2O
    3. SF4
    4. Cl2O
  3. In Rutherford's gold foil experiment, most alpha particles passed through the foil with little or no deflection. What does this observation suggest about the structure of the atom? (2 PTS)
    1. The gold foil was too thin to deflect the alpha particles significantly.
    2. Alpha particles are too small to interact with atoms.
    3. Most of the atom is empty space, with the positive charge concentrated in a tiny nucleus.
    4. The atom is a uniform sphere of positive charge with electrons embedded throughout.
  4. What is the charge on a proton compared to the charge on an electron? (2 PTS)
    1. The proton has twice the charge of an electron.
    2. The proton has the same magnitude of charge as an electron but opposite in sign.
    3. The proton has a smaller charge than an electron.
    4. The proton has no charge.
  5. Which of the following correctly names the ionic compound NaClO2? (2 PTS)
    1. Sodium chlorate
    2. Sodium hypochlorite
    3. Sodium chlorite
    4. Sodium chlorine oxide

True or False

  1. According to Dalton's atomic theory, a given compound always has the same relative number and kind of atoms. (1 PTS)
  2. Neutrons carry a negative electrical charge. (1 PTS)
  3. The nucleus of an atom accounts for nearly the entire mass of the atom. (1 PTS)

Problem Solving

  1. Naturally occurring chlorine is 75.78% ^35Cl (atomic mass 34.969 u) and 24.22% ^37Cl (atomic mass 36.966 u). Calculate the atomic weight of chlorine. (5 PTS)
  2. An atom contains 82 protons, 82 electrons, and 126 neutrons. Write the complete chemical symbol (with superscript and subscript) for this atom, and identify the element. (5 PTS)

Answer key

Multiple Choice

  1. 1.B — Dalton's second postulate states that all atoms of a given element are identical, but atoms of one element are different from atoms of all other elements.
  2. 2.B — Ionic compounds are composed of a metal combined with a nonmetal. Na2O contains sodium (a metal) and oxygen (a nonmetal), making it ionic. The other compounds are composed entirely of nonmetals, making them molecular compounds.
  3. 3.C — Rutherford's nuclear model explains that most alpha particles pass through undeflected because most of the atom is empty space. Only particles that come very close to the tiny, highly charged nucleus are deflected at large angles.
  4. 4.B — The charge of a proton is +1.602 × 10-19 C, which is opposite in sign but equal in magnitude to the charge of an electron at -1.602 × 10-19 C.
  5. 5.C — The polyatomic ion ClO2- is named chlorite. When combined with sodium, the compound is named sodium chlorite.

True or False

  1. 1.True — This is Dalton's fourth postulate, which forms the basis of the law of constant composition.
  2. 2.False — Neutrons are electrically neutral, which is how they received their name. They carry no electrical charge.
  3. 3.True — Because protons and neutrons are much more massive than electrons (it takes 1836 electrons to equal the mass of one proton), the nucleus, which contains the protons and neutrons, accounts for nearly all of the atom's mass.

Problem Solving

  1. 1.Atomic weight = (0.7578 × 34.969 u) + (0.2422 × 36.966 u) = 26.496 u + 8.953 u = 35.45 u — The atomic weight is calculated as the weighted average of the isotopic masses, where each mass is multiplied by its fractional abundance and the results are summed.
  2. 2.The element with 82 protons is lead (Pb). The mass number is 82 + 126 = 208. The complete symbol is ^20882Pb. — The atomic number (number of protons) identifies the element as lead. The mass number is the sum of protons and neutrons. The symbol format is ^(mass number)atomic numberElement.