In the second row of the periodic table, Be, N, and Ne all have endothermic (unfavorable) electr

step 1 All right, guys, we're doing problem 126 in Chapter 7. So in the second row of the PRR table, Bo

In the second row of the periodic table, Be, N, and Ne all...

In the second row of the periodic table, $\mathrm{Be}, \mathrm{N}$, and $\mathrm{Ne}$ all have endothermic (unfavorable) electron affinities, whereas the other second-row elements have exothermic (favorable) electron affinities. Rationalize why Be, $\mathrm{N}$, and Ne have unfavorable electron affinities.

Key Concepts

Subshell Stability and Electronic Structure

Subshell stability refers to the extra stability observed in atoms with half-filled or completely filled orbitals. For instance, atoms with a half-filled p-subshell or a completely filled electron configuration enjoy a degree of symmetry and exchange energy stabilization. Adding an electron to such configurations can disrupt this stability; the incoming electron may be forced into a higher energy orbital or introduce additional electron–electron repulsion, which makes the process endothermic. This concept rationalizes why elements with particularly stable electron configurations may exhibit unfavorable (endothermic) electron affinities.

Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gas phase. It reflects the tendency of an atom to accept an electron; a large, negative electron affinity indicates that energy is released upon electron addition (favorable), while a positive (endothermic) electron affinity means that energy must be supplied. The concept encompasses both the electronic attraction of the nucleus for an extra electron and the repulsion effects arising from electron–electron interactions.

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom’s orbitals, and it plays a key role in determining an atom’s chemical and physical properties. When an electron is added, it must occupy an orbital that may already be filled or partially filled, and this new electron experiences different shielding and penetration effects. In elements with specific configurations, like a completely filled or half-filled subshell, the added electron might enter an orbital that is higher in energy or disturb a particularly stable arrangement, leading to an unfavorable electron affinity.

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