This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Ionization Energy and Electron Affinity”.
1. What is ionization energy?
a) Energy absorbed by an atom to eject an electron
b) Energy released by an atom to eject an electron
c) Energy absorbed by an electron to eject an atom
d) Energy released by an electron to eject an atom
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Explanation: Ionization energy is the energy required to remove an electron from a gaseous atom, ion, or molecule. These follow certain trends in the periodic table with across columns and rows. Most elements have a first ionization energy associated with them.
2. What reaction corresponds with first ionization energy?
a) A+ + e– = A
b) A2+ = A+ + 2e–
c) A = A+ + e–
d) A = A+ + 2e–
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Explanation: The first ionization energy is the energy required to remove an electron from an uncharged atom to form a positively charged ion. Hence, by absorbing energy, the atom releases an electron and forms a charged cation. First ionization energy has well defined periodic table trends.
3. What reaction corresponds with second ionization energy?
a) A+ = A2+ + e–
b) A = A+ + 2e–
c) 2A = 2A+ + 2e–
d) A = A+ + e–
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Explanation: The second ionization energy is the energy required to remove an electron from a cation with charge +1. Hence, by absorbing energy, the atom releases an electron and forms another cation with a charge of +2.
4. What is the most difficult atom to ionize?
a) Hydrogen
b) Helium
c) Beryllium
d) Neon
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Explanation: The electron in Helium is most closely bound to the nucleus electrostatically, hence having the least distance between these two. Hence it requires a large amount of energy to remove the outermost duplet electron to create an ionized atom and cation.
5. What group of the periodic table is easiest to ionize?
a) Noble Gases
b) Alkali metals
c) Alkali earth metals
d) Transition metals
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Explanation: Alkali metals only have one electron in their outermost shell. This makes it easy to eject it due to a weak electrostatic force with the nucleus. Moreover, ejecting this electron will create a very stable octet for the corresponding cations.
6. What is electron affinity?
a) Energy released by ejecting an atom from an electron
b) Energy absorbed by ejecting an electron from an atom
c) Energy released by adding an electron to an atom
d) The magnetic attraction between an external electron and an atom
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Explanation: Electron Affinity is the energy of an atom released in the process of adding an electron. This has defined trends in the periodic table, with the halogens having the highest electron affinity. Noble gases do not have a measured or definite value with their electron affinity.
7. What reaction corresponds with electron affinity?
a) A–(g) + e– = A2-(g)
b) A(g) = A+(g) + e–
c) A(g) + e– = A–(g)
d) A(g) = A–(g) + e
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Explanation: Electron Affinity is the energy of an atom released in the process of adding an electron. By absorbing this electron, an atom becomes a negatively charged cation. All these are in the gaseous state, and hence standard values are also in the gaseous form.
8. If the enthalpy of electron affinity for chlorine is -347 kJ/mole at 0K, what is its electron affinity if the Faraday constant is 96.485 kJ/mol/Ev?
a) -1.80 ev
b) 3.60 ev
c) -3.60 ev
d) 1.80 ev
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Explanation: Standard enthalpy change = \(\frac{-347\frac{kJ}{mole}}{\frac{96.485\frac{kJ}{mole}}{ev}}\) = -3.60 ev. Since the change in enthalpy is -3.60 eV, the electron affinity equation is the reverse reaction of the same. Hence, the electron affinity for chlorine is 3.60 ev.
9. What does it mean if the electron affinity value is negative?
a) Atom is unreactive/ extremely stable
b) It is ionization energy, not electron affinity
c) Energy was absorbed, not released
d) Negative ion is unstable with respect to the atom and an electron
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Explanation: Since electron affinity is energy released, the process must be endothermic and hence a positive value. Negative electron affinity does not exist except if the ion is unstable compared to the corresponding electron and atom. This normally occurs for noble gases hence they do not have a properly measured electron affinity.
10. Which noble gas has the highest first ionization energy?
a) Helium
b) Krypton
c) Xenon
d) Neon
View Answer
Explanation: The electron in Helium is most closely bound to the nucleus electrostatically. Although this is the case with all noble gases, helium has the shortest distance between its nucleus and electron, hence the greatest electrostatic force. Hence it requires a large amount of energy to remove the outermost duplet electron to create an ionized atom and cation.
11. Which element has the highest electron affinity?
a) Helium
b) Hydrogen
c) Neon
d) Chlorine
View Answer
Explanation: Chlorine has the highest electron affinity of 3.60 ev. This is greater than all other elements as it requires a lot of energy to release an electron. On the contrary, chlorine needs to absorb one electron to obtain the stable octet electron configuration. Noble gases do have clearly measured electron affinities.
Sanfoundry Global Education & Learning Series – Physical Chemistry.
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