Passage
Dmitri Mendeleev is credited with grouping the elements by atomic mass and observing that similar properties emerge periodically. Henry Moseley then determined that a fundamental property, which Ernest Rutherford later called the atomic number, is more important than atomic mass for ordering the elements.As the periodic table took shape, scientists noted certain properties and trends. For example, Rayleigh and Ramsay observed that some elements are unreactive and gave them the name noble gases. But it was not until Niels Bohr described his model of the atom that scientists understood why noble gases are stable.Another important trend was discovered by Linus Pauling. He was the first to identify electronegativity as a way to describe bonds that are neither completely ionic nor completely covalent. Pauling assigned fluorine the highest electronegativity value of 4.0 because of its strong tendency to attract electrons when bonded to other atoms. All other atoms were assigned values relative to fluorine. This became known as the Pauling electronegativity scale.Scientists identified other trends based on x-ray crystallography and reactivity studies. Figure 1 shows the first ionization energy of the elements, and Figure 2 shows electron affinity.
Figure 1 First ionization energy of elements
Figure 2 Electron affinity of several elements (larger negative values indicate greater electron affinity)
-Oxygen is the most electronegative element of Group 6A. However, it also has the lowest electron affinity in the group. What factor can be used to explain this discrepancy?

Question

Passage
Dmitri Mendeleev is credited with grouping the elements by atomic mass and observing that similar properties emerge periodically. Henry Moseley then determined that a fundamental property, which Ernest Rutherford later called the atomic number, is more important than atomic mass for ordering the elements.As the periodic table took shape, scientists noted certain properties and trends. For example, Rayleigh and Ramsay observed that some elements are unreactive and gave them the name noble gases. But it was not until Niels Bohr described his model of the atom that scientists understood why noble gases are stable.Another important trend was discovered by Linus Pauling. He was the first to identify electronegativity as a way to describe bonds that are neither completely ionic nor completely covalent. Pauling assigned fluorine the highest electronegativity value of 4.0 because of its strong tendency to attract electrons when bonded to other atoms. All other atoms were assigned values relative to fluorine. This became known as the Pauling electronegativity scale.Scientists identified other trends based on x-ray crystallography and reactivity studies. Figure 1 shows the first ionization energy of the elements, and Figure 2 shows electron affinity.

Figure 1 First ionization energy of elements

Figure 2 Electron affinity of several elements (larger negative values indicate greater electron affinity)
-Oxygen is the most electronegative element of Group 6A. However, it also has the lowest electron affinity in the group. What factor can be used to explain this discrepancy?

Quizplus · Accepted Answer

11ecba2d_11c1_f0bf_a3bf_5d092e3a28a6_MD0008_00 Electronegativity is a qualitative measure of how strongly electrons are attracted to an atom within a bond. Group 6A (Group 16) elements follow the trend that electronegativity decreases going down the group on the periodic table. When bonded to another atom, oxygen strongly attracts electrons toward itself, creating unequal electron sharing that produces a dipole moment. In contrast, electron affinity (EA) is the quantitative measure of the energy change when an electron is added to an atom in the gas state. The more negative the change in energy, the more energy released upon addition of an electron. Although EA generally increases (becomes more negative) from left to right across a period, EA generally decreases (becomes more positive) going down a group because the electron is added at an increased distance from the nucleus. The exception to this trend is when an atom is very small (ie, first or second period). Small atoms such as oxygen and fluorine have several electrons crowded around a small nucleus, resulting in greater electron-electron repulsion. Adding another electron would increase repulsion forces even further, so it is more difficult to add an electron to oxygen than to a larger atom with lower repulsion forces. (Choice A) Oxygen is no more or less stable than other Group 6A elements, and its stability does not explain why its electron affinity breaks the pattern. (Choice C) Oxygen's valence electrons are less shielded from the nucleus than other Group 6A elements because its valence electrons are closer to the nucleus. (Choice D) Although it is true that oxygen does not have empty d orbitals in its valence shell, this does not explain why oxygen has a smaller electron affinity than expected. Educational objective: Electron affinity is the measure of energy change when an electron is added to an atom in the gaseous state. Electron-electron repulsions result in a decreased electron affinity.

Passage Dmitri Mendeleev Is Credited with Grouping the Elements by Atomic