Question

The first ionization energy of Ar and the electron affinity of \(\mathrm{Ar}\) are both positive values. What is the significance of the positive value in each case?

Short answer

The positive values of the first ionization energy and electron affinity of Ar indicate that both removing and adding an electron to a neutral Argon atom require energy input. This is because Argon has a full and stable outer electron shell, making it less likely to engage in electron exchange. Ionization energy represents the energy needed to remove an electron from an atom, while electron affinity is the energy change when an electron is added to an atom. In both cases, Argon's electron configuration results in endothermic processes that require energy to occur.

Step-by-step solution

Define Ionization Energy and Electron Affinity

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state, while electron affinity is the energy change that occurs when an electron is added to a neutral atom or ion in its gaseous state.

Discuss the Significance of Positive Ionization Energy for Ar

The first ionization energy of Ar refers to the amount of energy required to remove one electron from a neutral Argon atom. Since the value is positive, this signifies that energy must be supplied to remove an electron from the Argon atom. This is expected because removing an electron from an atom usually requires energy input, as electrons are attracted to the positive nucleus. In the case of Argon, it has a full outer electron shell with 18 electrons (2 in the first shell, 8 in the second shell, and 8 in the third shell). The full outer shell makes it very stable and less likely to lose or gain electrons, meaning it requires even more energy to remove one of these outer electrons.

Discuss the Significance of Positive Electron Affinity for Ar

Electron affinity is the energy change that occurs when an electron is added to a neutral Argon atom. In the case of Argon, a positive electron affinity indicates that the addition of an electron is an endothermic process, meaning it requires energy input. This happens because the Argon atom, with its stable full electron shell configuration, does not have a tendency to gain an additional electron. Thus, energy has to be supplied to force an extra electron to occupy a higher energy shell or an unfavorable position within the outer shell. In summary, the positive values of the first ionization energy and electron affinity of Ar signify that both processes of removing and adding an electron require energy input due to Argon's full outer electron shell configuration, which makes it very stable and less likely to engage in electron exchange.

Key concepts

Argon Stability

Argon is a unique element due to its highly stable electron configuration. It belongs to the noble gases group, and like other noble gases, it has a full outer electron shell. This specific structure consists of 18 electrons arranged as follows: 2 in the first shell, 8 in the second shell, and 8 in the third shell.

Having a full outer shell means argon doesn't easily react with other elements, as it doesn't readily lose or gain extra electrons. This makes argon extremely stable and unreactive under normal conditions. Its stable configuration minimizes the energy changes that usually drive chemical reactions, making it a preferred shield gas in environments where reactions need to be minimized.

Electron Removal

Removing an electron from an atom involves a concept known as ionization energy. For argon, the first ionization energy is the energy needed to remove the most loosely held electron, which is part of its full outer electron shell.

The positive ionization energy value of argon indicates that extracting an electron requires an input of energy. This need for energy arises because electrons are negatively charged and are naturally attracted to the positively charged nucleus. As a result, external energy must overcome this attraction to remove an electron.

In argon’s case, removing an electron is particularly challenging due to its stable, full outer shell configuration, requiring even more energy compared to elements with incomplete outer shells.

Electron Affinity

Electron affinity refers to the energy change that occurs when an electron is added to a neutral atom. For argon, this process has a positive electron affinity value, which indicates that adding an electron is not energetically favorable and requires energy input.

Typically, when an electron is added to an atom, energy is released. However, argon’s full outer shell means there isn't a natural space for an additional electron. Consequently, if an electron is forced to stick with an argon atom, the location for this electron becomes energetically less favorable, causing the process to be endothermic.

Hence, argon’s positive electron affinity reflects its resistance to gaining additional electrons due to its stable electronic configuration.

Endothermic Process

An endothermic process needs energy to proceed, and this is true when either removing or adding electrons in the case of argon.

When dealing with ionization energy and electron affinity, both cases for argon are examples of endothermic reactions. Removing an electron from argon requires energy input because of the attraction between the electron and the nucleus, and argon's highly stable electron configuration increases this requirement.

Similarly, adding an electron is an endothermic process for argon because the stable electron configuration resists the integration of an additional electron. This energy input to force an electron into the atom highlights the inherent stability in argon's electron arrangement.