Question

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

Short answer

In summary: For Mg and K: a. Mg has a more favorable electron affinity. b. Mg has a higher ionization energy. c. K has a larger atomic size. For F and Cl: a. F has a more favorable electron affinity. b. F has a higher ionization energy. c. Cl has a larger atomic size.

Step-by-step solution

a. More favorable (exothermic) electron affinity

Since Mg and K belong to different periods, but Mg is higher up in the periodic table than K, Mg has a more favorable electron affinity.

b. Higher ionization energy

Since Mg and K belong to different groups, but Mg is to the right of K, Mg has a higher ionization energy.

c. Larger size

Since Mg and K belong to different periods, but Mg is higher up in the periodic table than K, K has a larger atomic size. For F (Fluorine) and Cl (Chlorine):

a. More favorable (exothermic) electron affinity

F and Cl belong to the same group, but F is higher up than Cl, F has a more favorable electron affinity.

b. Higher ionization energy

F and Cl belong to the same group, but F is higher up than Cl, F has a higher ionization energy.

c. Larger size

Since F and Cl belong to the same group, but F is higher up in the periodic table than Cl, Cl has a larger atomic size.

Key concepts

Electron Affinity

Electron affinity refers to the energy change that occurs when an atom gains an electron. A more favorable or exothermic electron affinity means that energy is released when an electron is added to an atom. This property is crucial for understanding how different elements interact with electrons.

• In general, elements on the right side of the periodic table have more favorable electron affinities because they are more eager to accept electrons to achieve a stable electronic configuration.
• For example, in the pair of fluorine (F) and chlorine (Cl), fluorine has a more favorable electron affinity. Being higher on the periodic table implies it exerts a stronger pull on additional electrons due to a smaller atomic radius and high electronegativity.
• In contrast, comparing magnesium (Mg) and potassium (K), magnesium typically has a more favorable electron affinity despite its position due to being closer to completing its shell with fewer electrons.

Understanding these trends supports predicting how elements will behave in reactions, where the acceptors of new electrons play a vital part.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. It is a key factor in understanding the reactivity of elements. A higher ionization energy indicates that an atom holds onto its electrons more tightly.

• Atoms higher and to the right on the periodic table generally have higher ionization energies. This trend arises because atoms in these positions have more protons, increasing the nuclear charge and holding electrons more tightly.
• In the case of magnesium (Mg) and potassium (K), magnesium has a higher ionization energy. Mg is to the right of K and has a greater positive charge in its nucleus, thus holding its electrons more firmly.
• Comparing fluorine (F) and chlorine (Cl), fluorine also exhibits a higher ionization energy as it is above chlorine in the periodic table, reflecting its smaller size and greater attraction for electrons.

Recognizing ionization energy trends is essential for predicting how atoms interact, especially in processes like forming cations where electrons are detached.

Atomic Size

Atomic size, or atomic radius, refers to the distance from the nucleus to the outermost shell of an electron. This measure helps in understanding how atoms will pack and interact with one another chemically.

• As you move down a group in the periodic table, atomic size increases due to the addition of more electron shells which outweighs the increased nuclear charge in affecting size.
• For elements in the same period, moving left to right, atomic size decreases as electrons are added to the same shell while the nuclear charge increases, pulling the electrons closer.
• In comparing pairs such as magnesium (Mg) and potassium (K), potassium will have the larger atomic size since it is further down a group, meaning it has more electron shells.
• For fluorine (F) and chlorine (Cl), chlorine is larger as it is below fluorine in their shared column, indicating it has an additional electron shell.

Comprehending the trends in atomic size helps in predicting physical and chemical properties such as densities, melting points, and how elements bond.