Question

For each of the following pairs of elements \((\mathrm{C}\) and \(\mathrm{N})\) \((\mathrm{Ar}\) and \(\mathrm{Br})\) pick the atom with a. more favorable (exothermic) electron affinity. b. higher ionization energy. c. larger size.

Short answer

For the pair (C and N): a. N has a more favorable electron affinity. b. N has a higher ionization energy. c. C has a larger atomic size. For the pair (Ar and Br): a. Br has a more favorable electron affinity. b. Ar has a higher ionization energy. c. Br has a larger atomic size.

Step-by-step solution

Pair 1: C and N

First, let's analyze the pair of atoms, Carbon (C) and Nitrogen (N). They are both in the same period (period 2). a. Since N is to the right of C in period 2, it has a more favorable (exothermic) electron affinity. b. N is closer to the top right corner, so it has a higher ionization energy. c. C is larger in size compared to N, as the size decreases across a period.

Pair 2: Ar and Br

Next, let's analyze the pair of atoms, Argon (Ar) and Bromine (Br). They are both in the same group (group 18, noble gases, and group 17, halogens, respectively). a. Since Ar is a noble gas, it has no electron affinity, while Br has a favorable (exothermic) electron affinity. b. Ar is in a higher period (period 3) compared to Br (period 4), so Ar should have a higher ionization energy. c. Br is lower on the periodic table (period 4) compared to Ar (period 3), so Br has a larger atomic size.

Summary of the answers

For the pair (Carbon and Nitrogen): a. Nitrogen has a more favorable electron affinity. b. Nitrogen has a higher ionization energy. c. Carbon has a larger atomic size. For the pair (Argon and Bromine): a. Bromine has a more favorable electron affinity. b. Argon has a higher ionization energy. c. Bromine has a larger atomic size.

Key concepts

Electron Affinity

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom to form a negative ion. This is often measured in kilojoules per mole (kJ/mol). A more negative value indicates a more favorable or exothermic process. Electrons are attracted to atoms with higher electron affinity as these atoms can accommodate additional electrons more readily.

• Nitrogen (N) and Bromine (Br) have higher electron affinities compared to their pairings (Carbon and Argon) because they have more stable electronic configurations once they acquire an extra electron.
• In general, electron affinity increases across a period from left to right due to increasing nuclear charge, making atoms more able to attract additional electrons.
• Electron affinity generally decreases down a group because electrons are added at greater distances from the nucleus, reducing the effective nuclear attraction.

Ionization Energy

Ionization energy is the energy required to remove an electron from a neutral atom in the gas phase, making it a crucial concept in understanding periodic trends. Atoms with high ionization energy hold onto their electrons tightly, which typically means they have a compact electronic arrangement.

• Nitrogen has a higher ionization energy compared to Carbon due to its greater effective nuclear charge, requiring more energy to remove an outermost electron.
• Argon also has a higher ionization energy than Bromine as Argon is a noble gas, efficiently holding its valence electrons.
• Ionization energy does increase as we move across a period from left to right but decreases as we move down a group.

Atomic Size

Atomic size, often referred to as atomic radius, is the measure of the distance from the nucleus to the outermost occupied electron shell. This size can dramatically influence an element's chemical behavior.

• Carbon is larger in size than Nitrogen because within the same period, atomic size decreases from left to right. This is due to increasing nuclear charge pulling the outer electrons closer.
• Bromine is larger than Argon because atomic size increases down a group. Here, the outer electrons occupy higher energy levels, further from the nucleus.
• When comparing sizes, remember that more protons (increased nuclear charge) within the same period result in a smaller radius, while more electron shells (moving down a group) increase atomic size.