Question

Consider the following statement: "Because oxygen wants to have a negative two charge, the second electron affinity is more negative than the first." Indicate everything that is correct in this statement. Indicate everything that is incorrect. Correct the incorrect statements and explain.

Short answer

The given statement is partially correct - oxygen does want to have a negative two charge to attain a stable electronic configuration. However, the statement incorrectly claims the second electron affinity is more negative than the first. In reality, the first electron affinity is negative, but the second electron affinity is positive due to repulsion between the incoming electron and the negatively charged ion (O^-). The corrected statement should be: "Because oxygen wants to have a negative two charge, the first electron affinity is negative. However, the second electron affinity is positive since the incoming electron faces repulsion from the negatively charged ion (O^-)."

Step-by-step solution

Understanding Electron Affinity

Electron affinity is the energy change associated with adding an electron to an atom or ion. A more negative electron affinity indicates that adding an electron to an atom is a more favorable process. In general, electron affinity becomes more negative as you go from left to right across a period in the periodic table because the effective nuclear charge increases, pulling additional electrons more tightly to the nucleus.

Oxygen's Preferred Charge

Oxygen, with atomic number 8, has six electrons in its outermost shell. To achieve the stable electronic configuration, it prefers to gain two more electrons and thus acquire a negative two charge (O^{2-}). This is because gaining two electrons would fill its 2p orbital, making it more stable.

First Electron Affinity

The first electron affinity is the energy change associated with adding one electron to an atom. For oxygen, this process is favorable, meaning energy is released and the electron affinity value is negative. This is because the added electron will fill one of the unoccupied spaces in the 2p orbital of oxygen.

Second Electron Affinity

The second electron affinity is the energy change associated with adding an additional electron to the ion (O^-). For oxygen, this process is less favorable compared to the first electron affinity because the incoming electron faces repulsion from the negatively charged ion (O^-). As a result, energy must be added for this process to occur, making the second electron affinity positive.

The Correct and Incorrect Parts of the Statement

The only correct part of the given statement is the fact that oxygen wants to have a negative two charge in order to achieve a stable electronic configuration. The incorrect part of the statement is that the second electron affinity is more negative than the first. In reality, the second electron affinity is positive due to the repulsion between the incoming electron and the negatively charged ion (O^-).

Correcting the Statement and Explanation

The corrected statement should be: "Because oxygen wants to have a negative two charge, the first electron affinity is negative. However, the second electron affinity is positive since the incoming electron faces repulsion from the negatively charged ion (O^-)." This properly explains that the first electron affinity is favorable due to oxygen's desire to achieve a stable electronic configuration, while the second electron affinity is less favorable due to electrostatic repulsion.

Key concepts

Energy Change

The concept of 'energy change' is fundamental in understanding electron affinity. When an atom gains an electron, it undergoes a change in energy, known as electron affinity. This change can be exothermic (releasing energy, hence a negative value) or endothermic (absorbing energy, hence a positive value).

Take note that when electrons are added to an atom, the first addition will typically release energy making the electron affinity negative. However, adding more electrons after the atom achieves a stable electron configuration requires energy, which makes subsequent electron affinities less negative or even positive. For example, oxygen's first electron affinity is negative due to the release of energy as it moves closer to stability, but the second electron affinity is unexpectedly positive because the added electron is repelled by the already negative ion.

Atomic Structure

Understanding 'atomic structure' is crucial as it determines how an element behaves when it gains or loses electrons. The atomic structure consists of a nucleus containing protons and neutrons, surrounded by electrons arranged in various orbital levels. Elements seek to achieve a stable electron configuration similar to the nearest noble gas, which usually means having a full outermost electron shell.

For instance, oxygen has six electrons in its valence shell (outermost shell) and requires two more to achieve stability, akin to neon. Therefore, its first electron affinity is significant, but the positive value in the second electron affinity indicates the energy challenge of adding another electron against the electrostatic repulsion of the newly formed O⁻ ion.

Periodic Trends

The 'periodic trends' in electron affinity are patterns observed across the periodic table. As we move from left to right across a period, electron affinities generally become more negative, indicating it is increasingly more energetically favorable to add an electron. This trend occurs due to an increase in 'effective nuclear charge', which attracts additional electrons more tightly.

However, there are exceptions to this trend. For instance, despite being to the right of oxygen in the periodic table, the electron affinity of fluorine is less negative than that of oxygen when comparing their first electron affinities. This is because of the small size of fluorine, causing electron-electron repulsion within its compact valence shell.

Electron Configuration

The 'electron configuration' of an atom can be considered a map of where its electrons reside. Electrons are distributed in orbitals around an atom’s nucleus, and the specific arrangement in these orbitals is termed as the electron configuration. For elements desiring stability, the electron configuration gives insight into the number of electrons needed to achieve a full valence shell.

Oxygen, for example, has an electron configuration of 1s² 2s² 2p⁴. In aiming for a stable electron configuration, oxygen needs two additional electrons to fill its 2p orbital. Understanding an atom's electron configuration helps in predicting how it will interact with other atoms, particularly in its affinity for gaining electrons.

Effective Nuclear Charge

The 'effective nuclear charge' (Zeff) can be thought of as the net positive charge experienced by an electron from the nucleus, taking into account electron shielding and repulsion from other electrons. It influences an atom’s electron affinity as a higher Zeff usually equates to a greater pull on additional electrons, making the addition process energetically more favorable.

As we consider the addition of an electron to oxygen, we are observing the effects of its Zeff. The first electron affinity is negative due to a strong effective nuclear charge that pulls the electron in. Nonetheless, once the oxygen atom gains an electron and becomes O⁻, its Zeff on the added electron diminishes because the electron-electron repulsion reduces the attractive force of the nucleus on the incoming electron.

Ionic Charge

The 'ionic charge' refers to the electric charge an atom holds when it gains or loses electrons to achieve a stable electron configuration. Atoms can become ions with positive (cations) or negative (anions) charges. Oxygen typically forms an anion with a charge of -2 (O²⁻) by gaining two electrons, completing its valence shell which results in a stable electronic arrangement.

While oxygen desires a -2 charge, achieving it through the addition of the second electron is energetically less favorable than the first. The ionic charge impacts the energy change when adding electrons; for oxygen, this means the first electron affinity is negative, as expected, but the second electron affinity becomes positive due to repulsion between the negatively charged ion and the additional electron.