Question

For each of the following pairs of elements \(\begin{array}{ll}(\mathrm{Mg} \text { and } \mathrm{K}) & (\mathrm{F} \text { and } \mathrm{Cl})\end{array}\) pick the atom with a. more favorable (exothermic) electron affinity. b. higher ionization energy. c. larger size.

Short answer

The short answer for the given question is: a. More favorable (exothermic) electron affinity: \(Mg\) and \(F\). b. Higher ionization energy: \(Mg\) and \(F\). c. Larger size: \(K\) and \(Cl\).

Step-by-step solution

Electron Affinity

Both Mg and K belong to the same group 2 (alkaline earth metals) and group 1 (alkali metals) respectively, meaning that their electron affinity follows the periodic table trend. As we move from left to right on the periodic table, electron affinity generally increases. Therefore, Mg has a more favorable (exothermic) electron affinity than K.

Ionization Energy

Ionization energy also follows the periodic table trend, meaning that it generally increases from left to right and decreases from top to bottom. Since Mg is to the right of K, Mg has a higher ionization energy.

Size

The atomic size generally decreases from left to right and increases from top to bottom. Because K is below Mg, K has a larger size than Mg. #Step 2: Compare F and Cl#

Electron Affinity

Both F and Cl are part of the group 17 (halogens), meaning that their electron affinity follows the periodic table trend. As we move down a group, the electron affinity generally decreases. Therefore, F has a more favorable (exothermic) electron affinity than Cl.

Ionization Energy

Ionization energy generally increases as we move from left to right and decreases as we move down within a group. Since F is above Cl, F has a higher ionization energy.

Size

The atomic size generally decreases as we move from left to right and increases as we move down a group. Since Cl is below F, Cl has a larger size than F. So, the final answers are: a. more favorable (exothermic) electron affinity: Mg and F. b. higher ionization energy: Mg and F. c. larger size: K and Cl.

Key concepts

Electron Affinity

When we talk about electron affinity, we're discussing the energy change that occurs when an atom gains an electron. In simpler terms, it's about how much an atom "wants" an additional electron. The more negative (or exothermic) the value, the more an atom desires to gain an electron.

• As you move from left to right across the periodic table, elements generally have a stronger pull for electrons. This means their electron affinity becomes more negative. For example, elements like fluorine (F) have very high electron affinities because they are closer to achieving a full outer electron shell.
• When you move down a group in the periodic table, electron shells are added. This additional distance diminishes the nucleus's ability to attract electrons, leading to less negative electron affinities.

In our exercise, magnesium (Mg) has more favorable electron affinity than potassium (K) because it is further to the right in the periodic table. Similarly, fluorine (F) has a more favorable electron affinity than chlorine (Cl) because it is higher up in its group.

Ionization Energy

Ionization energy is the amount of energy needed to remove an electron from an atom in the gaseous state. It gives us insight into how strongly an atom holds onto its electrons. The higher the ionization energy, the more difficult it is to remove an electron.

• Lithium (Li) to Neon (Ne) trend shows ionization energy increases across a period from left to right, due to stronger nuclear pull without adding extra shielding electrons.
• Down a group, like hydrogen (H) to francium (Fr), ionization energy decreases as the increased distance and shielding make it easier to remove an outer electron.

In our examples, magnesium (Mg) has a higher ionization energy than potassium (K) because it is further to the right. On the other hand, fluorine (F) possesses a higher ionization energy than chlorine (Cl), since it is higher up in their shared group. The periodic trend of increasing ionization energy across a period helps in quickly understanding these relationships.

Atomic Size

Atomic size, or atomic radius, refers to how big an atom is. This can seem like a simple measure, but it actually offers a lot of insight into an element's characteristics and behaviors.

• Atomic size decreases from left to right across a period. This is because more protons are added to the nuclei, pulling the electron cloud closer.
• As you go down a group, atoms get larger because additional electron shells are added, increasing the overall size despite the increased proton number.

In our exercise, potassium (K) is larger than magnesium (Mg) because it is positioned lower down a group in the periodic table. Conversely, chlorine (Cl) is larger than fluorine (F) due to its placement lower in the same group. Understanding atomic size trends provides insights into why some atoms are less or more reactive, how easily they form ions, and their overall chemical behavior.