GRE Subject Test: Chemistry : Electron Affinity

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

varsity tutors app store varsity tutors android store

Example Questions

Example Question #31 : General Chemistry

Which of the given atoms has the lowest electron affinity?

Possible Answers:

Sr

Be

Ra

Ca

Correct answer:

Ra

Explanation:

Beryllium, calcium, strontium, and radium are all alkaline earth metals in the same group of the periodic table.

The electron affinity, a measure of the energy released when an atom gains an electron (an exothermic reaction), decreases from the top of a group (column) to the bottom. The trends in electron affinity can be correlated with ionization energy. When a smaller atom gains an electron, the force between the electron and nucleus is greater than in a larger atom; thus, more energy is released when this “bond” between the nucleus and electron is formed in a smaller atom than in a larger atom, meaning that smaller atoms will have greater electron affinity. Radium is the farthest down the group of alkaline earth metals, and will have the largest atomic radius of the answer choices, giving it the lowest electron affinity.

Example Question #6 : Atoms, Elements, And The Periodic Table

Which of the given atoms has the greatest electron affinity?

Possible Answers:

Cl

Al

Na

P

Correct answer:

Cl

Explanation:

Sodium, aluminum, phosphorus, and chlorine are all in the same row (period) of the periodic table.

The electron affinity, a measure of the energy released when an atom gains an electron (an exothermic reaction), increases from left to right across the periodic table because when a smaller atom gains an electron, the force between the electron and nucleus is greater than with a larger atom. More energy is released when this “bond” between the nucleus and electron is formed. Chlorine has the smallest atomic radius of the answer choices because it is located farthest to the right of the period; thus, chlorine will also have the greatest attractive force between its nucleus and electrons, giving it the highest electron affinity.

Example Question #32 : General Chemistry

Which element would experience the greatest energy loss when a neutral atom in the gaseous phase gains one additional electron?

Possible Answers:

Cesium

Chlorine

Krypton

Lithium

Fluorine

Correct answer:

Fluorine

Explanation:

This question refers to electron affinity, which is defined as the energy given off when a neutral atom in the gas phase gains an extra electron.

Electron affinity increases for elements towards the top and right of the periodic table, so the elements in the top right lose the most energy when gaining an electron. Another way of thinking is that they lose energy, but gain stability. Of the available answers, the element to the most upper right of the periodic table is fluorine.

Example Question #31 : General Chemistry

Atoms have characteristic electronegativities and electron affinities. Which of the following best describes the difference between these two terms?

Possible Answers:

Electronegativity describes an atom's tendency to accept electrons, while electron affinity describes an atom's tendency to retain its current electron configuration

Electronegativity describes an atom's tendency to retain its current electron configuration, while electron affinity describes an atom's tendency to accept electrons

Electronegativity describes the potential an atom has to give up its electrons, whereas electron affinity describes the potential an atom has to gain electrons

Depending on the specific case, the electronegativity of an atom is determined by its electron affinity

Electronegativity and electron affinity are two terms describing the same atomic phenomenon

Correct answer:

Electronegativity describes an atom's tendency to accept electrons, while electron affinity describes an atom's tendency to retain its current electron configuration

Explanation:

Electronegativity and electron affinity can be easily confused. Both terms describe resistance to electron gain, but they do so by different classifications. Electronegativity describes how readily an atom will become an anion, or how easily it will accept an electron. The halogens have extremely high electronegativities, while the noble gases have virtually zero electronegativity. In contrast, electron affinity describes the energy change when an electron is added to an atom. The halogens, again, have very high electron affinities. The noble gases will sometimes have negative electron affinities, indicating that it is an exothermic process to remove an electron from these elements.

Example Question #917 : Mcat Physical Sciences

Electronegativity is an important concept in physical chemistry, and often used to help quantify the dipole moment of polar compounds. Polar compounds are different from those compounds that are purely nonpolar or purely ionic. An example can be seen by contrasting sodium chloride, NaCl, with an organic molecule, R-C-OH. The former is purely ionic, and the latter is polar covalent.  

When comparing more than one polar covalent molecule, we use the dipole moment value to help us determine relative strength of polarity. Dipole moment, however, is dependent on the electronegativity of the atoms making up the bond. Electronegativity is a property inherent to the atom in question, whereas dipole moment is a property of the bond between them.

For example, oxygen has an electronegativity of 3.44, and hydrogen of 2.20. In other words, oxygen more strongly attracts electrons when in a bond with hydrogen. This leads to the O-H bond having a dipole moment.

When all the dipole moments of polar bonds in a molecule are summed, the molecular dipole moment results, as per the following equation.

Dipole moment = charge * separation distance

Electronegativity is associated with another function, electron affinity. What is true of electron affinity?

Possible Answers:

It is exothermic for both chlorine and sodium

Electron affinity is a vector quantity

The second electron affinity is always much lower in magnitude than the first

It is equal for sodium and for chlorine

It is endothermic for chlorine and exothermic for sodium

Correct answer:

It is exothermic for both chlorine and sodium

Explanation:

Chlorine has a great thermodynamic desire to capture an electron, thus taking on the electronic structure of a stable noble gas. This causes chlorine to release energy when it captures an electron as it becomes more stable.

Sodium, on the other hand, would prefer to lose an electron and gain the configuration of a noble gas. Adding an electron would however award some stability to sodium, due to the complete s orbital that this would ensue.

Second electron affinity is usually encountered for such elements as oxygen and sulfur, which form anions with the addition of two electrons. The first electron affinity gives you O- or S-, and so it takes significant energy to add another electron to an already negative ion.

Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: