MCAT General Chemistry Practice Test 1: Atomic Structure and Periodic Trends

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Atoms are the building blocks of molecules and they consist of electrons surrounding a nucleus composed of neutrons and protons. The identity of an atom depends on how many protons it contains. The stability and/or reactivity of an atom often depends on how many neutrons and electrons it contains.

Nucleons themselves are composed of elementary particles known as quarks. Quarks are held together by the strong force to generate composite particles referred to as hadrons. This strong force, sometimes called the nuclear force, is also responsible for holding protons and neutrons together in the nucleus and overcomes other forces that may be present. Baryons, which are hadrons containing three quarks, form a charged nucleon when two up quarks and one down quark combine and uncharged nucleons when one up quark combines with two down quarks. Mesons, which are the other family of hadrons, are unstable particles composed of one quark and one antiquark.

1. An atom contains 29 hadrons comprised of two down quarks and one up quark and 28 hadrons comprised of two up quarks and one down quark. Which one of the following is the identity of the atom?

  • A. Iron-57
  • B. Nickel-57
  • C. Copper-57
  • D. Nickel-58

2. An excited electron drops down to its ground state and in the process a photon of light with a wavelength of 525 nm is emitted. Which of the following types of electromagnetic radiation could the photon be?

  • A. Infrared
  • B. Visible light
  • C. X-ray
  • D. Cannot be determined from the information given

3. A scientist in a laboratory observes a nucleon composed of three quarks with charges of +2/3 e, -1/3 e, and -1/3 e respectively. Which of the following best describes the nucleon?

  • A. The particle is a neutron and it contains two down quarks.
  • B. The particle is a proton and it contains two down quarks.
  • C. The particle is a neutron and it contains one down quark.
  • D. The particle is a proton and it contains one down quark.

4. The first, second, and third ionization energies for strontium are 549.5 kJ/mol, 1064.2 kJ/mol, and 4138 kJ/mol respectively. Why is the third ionization energy so much higher than the first two ionization energies?

  • A. The third electron is being removed from a completely full subshell.
  • B. The third electron has a larger mass than the first two electrons being removed.
  • C. The third electron being removed is less attracted to the nucleus than the first two electrons.
  • D. The third electron is at a higher energy level than the first two electrons.

5. Particles with opposite charges attract one another and particles with like charges repel. How can protons, which are positively charged, coexist in the nucleus?

  • A. The neutrons in the nucleus prevent the protons from touching one another.
  • B. The nuclear force is stronger than the repulsive forces between protons.
  • C. Hadrons do not experience forces with one another.
  • D. The surrounding cloud of electrons generates an opposing force.