GRE Subject Test: Chemistry : Ionization Energy

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

Example Question #3 : General Chemistry

Ionization energy __________ and atomic radius __________ down a group of the periodic table.

Possible Answers:

increases . . . increases

decreases . . . increases

stays the same . . . decreases

increases . . . decreases

decreases . . . decreases

Correct answer:

decreases . . . increases

Explanation:

Elements within a group have the same number of valence electrons, but in increasing energy levels. Elements toward the bottom of a group have valence electrons with higher energies in larger orbitals. This results in a larger radius and a weaker attractive force between the nucleus and outer electrons. The ionization energy decreases as the electrons are more removed from the attraction of the nucleus.

When moving down a group, atomic radius increases and ionization energy decreases.

Example Question #4 : General Chemistry

For an atom of scandium, which of its ionization energies will be greatest?

Possible Answers:

4th ionization energy

1st ionization energy

3rd ionization energy

2nd ionization energy

Correct answer:

4th ionization energy

Explanation:

Ionization energy is the energy that an atom must absorb in order to release an electron. Metals have fairly low ionization energies, up until they develop a noble gas electron configuration. At that point, the ionization energy will spike due to the stability of the noble gas configuration. For example, sodium has a very low first ionization energy because it has only one valence electron, but a very high second ionization energy because removal of a second electron disrupts the noble gas configuration of the ion.

Based on its position on the periodic table, scandium shows that it can release three electrons before it develops a noble gas electron configuration (hence its tendency to become an ion with a charge of +3).

At this point, the atom will require a massive amount of absorbed energy in order to release a fourth electron. This means that the 4th ionization energy for scandium is the highest of the given options.

 

Example Question #1 : Ionization Energy

Which atom has the lowest first ionization energy?

Possible Answers:

Sr

Rb

Ca

K

Correct answer:

Rb

Explanation:

First ionization energy tends to decrease as you move downward and to the left on the periodic table. Of the given answer options, rubidium is the farthest down and to the left, so it has the lowest first ionization energy.

Example Question #2 : Ionization Energy

Which element would you expect to have the highest first ionization energy?

Possible Answers:

Astatine

Iodine

Fluorine 

Bromine 

Chlorine

Correct answer:

Fluorine 

Explanation:

Ionization energy is a property of an atom that describes the lowest energy needed to remove a electron from its valence shell in the ground state.

Ionization energy increases up and to the right on the periodic table. All the elements listed are halogens located in group 7A of the periodic table. Because fluorine is located at the top of the periodic table in group 7A, it will have the highest first ionization energy. Ionization energy can be though of as the inverse of atomic radius. That is, the closer the valence shell of electrons is to the nucleus, the larger the magnitude of electric attractive force, and thus, the more energy is required to strip that electron. 

Example Question #3 : Ionization Energy

Which element would you expect to have the highest first ionization energy?

Possible Answers:

Boron

Iron

Calcium

Oxygen

Aluminum

Correct answer:

Oxygen

Explanation:

Ionization energy is a property of an atom or ion that describes the lowest energy needed to remove a electron from it in the ground state.

Ionization energy increases up and to the right on the periodic table. Because oxygen is the highest and rightmost element of those listed, it will have the highest first ionization energy. Ionization energy can be though of as the inverse of atomic radius. That is, the closer the valence shell of electrons is to the nucleus, the larger the magnitude of electric attractive force, and thus, the more energy is required to strip that electron.

Example Question #4 : Ionization Energy

Which element would you expect to have the highest first ionization energy?

Possible Answers:

Sodium

Fluorine

Potassium

Lithium

Barium

Correct answer:

Fluorine

Explanation:

Ionization energy is a property of an atom or ion that describes the lowest energy needed to remove a electron from it in the ground state.

Ionization energy increases up and to the right on the periodic table. Because fluorine is located furthest to the top right on the periodic table in group 7A, it will have the highest first ionization energy.

Example Question #5 : Ionization Energy

Which element would you expect to have the highest first ionization energy?

Possible Answers:

Chlorine

Calcium

Barium

Silicon

Correct answer:

Chlorine

Explanation:

Ionization energy is a property of an atom or ion that describes the lowest energy needed to remove a electron from it in the ground state.

Ionization energy increases up and to the right on the periodic table. All the elements listed are either lower than or further to the left on the periodic table than chlorine, therefore chlorine has the highest ionization energy.

Example Question #6 : Ionization Energy

Which element would you expect to have the highest first ionization energy?

Possible Answers:

Selenium

Tellurium

Sulfur

Oxygen

Correct answer:

Oxygen

Explanation:

Ionization energy is a property of an atom or ion that describes the lowest energy needed to remove a electron from it in the ground state.

Ionization energy increases up and to the right on the periodic table. All the elements listed are chalcogens located in group 6A of the periodic table. Because oxygen is located furthest to the top right on the periodic table in group 6A, it will have the highest first ionization energy.

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