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Chapter 9: Problem 23

Some electron affinities are negative quantities, and some are zero or positive. Why is this not also the case with ionization energies?

Short Answer

Expert verified
Ionization energy is always positive because it always requires energy to be supplied to remove an electron from an atom or molecule, which is in contrast to electron affinity that can be either negative, positive or even zero as it refers to the energy change when an atom or molecule gains an electron.

Step by step solution

01

Understanding Electron Affinity

The electron affinity of an atom or molecule is the amount of energy released (or, in certain cases, absorbed) when an electron is added to a neutral atom or molecule to form a negative ion. Thus, it can result in either a release of energy (negative electron affinity value), absorption of energy (positive electron affinity value), or in some cases, no energy change (zero electron affinity).
02

Understanding Ionization Energy

Ionization energy is defined as the quantity of energy that must be supplied to remove an electron from a neutral atom or molecule to form a positive ion. Since this process always requires an input of energy to overcome the attractive forces that hold electrons in the atom, ionization energy is always a positive value.
03

Answering the Question Whether Ionization Energies can be Negative or Zero

Since ionization ALWAYS requires energy to be supplied (endothermic process) to remove an electron from an atom or molecule, it is impossible for ionization energy to be zero or negative. That is, there is no instance where removing an electron from an atom or molecule would release energy, which would be represented as a negative ionization energy.

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Most popular questions from this chapter

Answer each of the following questions: (a) Which of the elements \(P, A s,\) and \(S\) has the largest atomic radius? (b) Which of the following has the smallest radius: \(\mathrm{Xe}, \mathrm{O}^{2-}, \mathrm{N}^{3-},\) or \(\mathrm{F}^{-} ?\) (c) Which should have the largest difference between the first and second ionization energy: \(\mathrm{Al}, \mathrm{Si}, \mathrm{P},\) or \(\mathrm{Cl} ?\) (d) Which has the largest ionization energy: \(\mathrm{C}, \mathrm{Si}\), or \(\mathrm{Sn}\) ? (e) Which has the largest electron affinity: \(\mathrm{Na}, \mathrm{B}\) \(\mathrm{Al},\) or \(\mathrm{C} ?\)

Neither \(\mathrm{Co}^{2+}\) nor \(\mathrm{Co}^{3+}\) has \(4 \mathrm{s}\) electrons in its electron configuration. How many unpaired electrons would you expect to find in each of these ions? Explain.

A method for estimating electron affinities is to extrapolate \(Z_{\text {eff }}\) values for atoms and ions that contain the same number of electrons as the negative ion of interest. Use the data in the table on the next page to answer the questions that follow. $$\begin{array}{lll} \hline \begin{array}{l} \text { Atom or lon: } \\ \text { I(kJmol }^{-1} \text {) } \end{array} & \begin{array}{l} \text { Atom or lon: } \\ \text { I(kJmol }^{-1} \text {) } \end{array} & \begin{array}{l} \text { Atom or lon: } \\ \text { I(kJmol }^{-1} \text {) } \end{array} \\ \hline \text { Ne: 2080 } & \text { F: 1681 } & \text { O: } 1314 \\ \text { Na }^{+}: 4565 & \text { Ne }^{+}: 3963 & \text { F }^{+}: 3375 \\ \text { Mg }^{2+} \text { : 7732 } & \text { Na }^{2+}: 6912 & \text { Ne }^{2+}: 6276 \\ \text { A1 }^{\text {3 }^{+}: 11,577} & \text { Mg }^{3+}: 10,548 & \text { Na }^{3+}: 9540 \\ \hline \end{array}$$ (a) Estimate the electron affinity of \(F\), and compare it with the experimental value. (b) Estimate the electron affinities of \(\mathrm{O}\) and \(\mathrm{N}\) (c) Examine your results in terms of penetration and screening.

Sketch a periodic table that would include all the elements in the main body of the table. How many "numbers" wide would the table be?

Listed below are two atomic properties of the element germanium. Refer only to the periodic table on the inside front cover and indicate probable values for each of the following elements, expressed as greater than, about equal to, or less than the value for Ge. $$\begin{array}{lcc} \hline \text { Element } & \text { Atomic Radius } & \begin{array}{c} \text { First lonization } \\ \text { Energy } \end{array} \\ \hline \mathrm{Ge} & 122 \mathrm{pm} & 762 \mathrm{kJ} / \mathrm{mol} \\ \mathrm{Al} & ? & ? \\ \mathrm{In} & ? & ? \\ \mathrm{Se} & ? & ? \\ \hline \end{array}$$
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