Quiz 3 - Atomic Structure & Periodic Trends | Atomic Structure and Periodic Trends

1

Which element has the largest first ionization energy?

Nitrogen has a half-filled p-orbital, which provides additional stability and requires more energy to remove an electron compared to the other elements listed.

2

Which element has the largest atomic radius?

Atomic radius increases as you move down a group in the periodic table due to the addition of electron shells. Among the given options, potassium (K) is located the farthest down and to the left in the periodic table compared to bromine (Br), magnesium (Mg), and sodium (Na). This position indicates that potassium has the largest atomic radius among the elements listed.

3

Which is the electron configuration for an Fe(III) ion in its ground state?

The neutral iron (Fe) atom has the electron configuration [Ar] 4s2 3d6. When it forms an Fe(III) ion (Fe3+), it loses three electrons. The electrons are removed first from the 4s orbital, followed by the 3d orbital. Therefore, the electron configuration of Fe3+ is [Ar] 3d5.

4

How many valence electrons are in one ion of thiosulfate, S2O32-?

To determine the number of valence electrons in the thiosulfate ion (S2O32-), we need to consider the valence electrons of sulfur and oxygen and account for the extra electrons due to the 2- charge:

• Sulfur (S) has 6 valence electrons. There are 2 sulfur atoms, so 2 × 6 = 12 valence electrons from sulfur.
• Oxygen (O) has 6 valence electrons. There are 3 oxygen atoms, so 3 × 6 = 18 valence electrons from oxygen.
• The 2- charge indicates there are 2 extra electrons added to the total.

Adding these together: 12 (from sulfur) + 18 (from oxygen) + 2 (extra electrons due to the charge) = 32 valence electrons.

5

For which pair of species is the difference in radii the greatest?

The radius of an ion is influenced by both its charge and the number of electron shells. Li+ (lithium ion) is a cation with a +1 charge, resulting from the loss of its single valence electron. This significantly reduces its radius compared to the neutral lithium atom due to the loss of the outermost electron shell. O2- (oxide ion) is an anion with a -2 charge, resulting from the gain of two electrons, which significantly increases its radius due to increased electron-electron repulsion in the same electron shell.

Comparing these two, Li+ has a very small radius because it has only the 1s shell remaining, while O2- has a much larger radius because it has gained additional electrons, leading to increased repulsion among the electrons in the valence shell.

6

The electron configuration of cobalt (Z = 27) is 1s22s22p63s23p63d74s2. How many unpaired electrons are in a gaseous Co3+ ion in its ground state?

1. The electron configuration of neutral cobalt (Co) is [Ar] 3d7 4s2.
2. When cobalt forms a Co3+ ion, it loses three electrons. The electrons are lost first from the 4s orbital and then from the 3d orbital.
3. Removing two electrons from the 4s orbital and one from the 3d orbital, the electron configuration for Co³⁺ becomes [Ar] 3d6.

In the 3d6 configuration, the six electrons are distributed in the five d orbitals according to Hund's rule, which states that electrons fill degenerate orbitals singly before pairing. Thus, the configuration of 3d6 will have four unpaired electrons.

7

Which element has the highest electron affinity?

Electron affinity generally becomes more negative across a period and less negative down a group. Fluorine, being at the top of group 17, has the highest (most negative) electron affinity.

8

Which atom has the largest atomic radius?

Atomic radius increases down a group and decreases across a period. Selenium (Se) is below sulfur (S) and chlorine (Cl) in the periodic table and to the left of bromine (Br), giving it the largest atomic radius among the given options.

9

Which of the following isoelectronic species has the largest radius?

Isoelectronic species have the same number of electrons. In this case, all listed species have 18 electrons (same as argon). The size of isoelectronic species depends on the nuclear charge: the higher the positive charge, the smaller the radius, because the electrons are pulled closer to the nucleus.

• K+ (19 protons)
• Ca2+ (20 protons)
• S2- (16 protons)
• P3- (15 protons)

The more protons in the nucleus, the stronger the attraction to the electrons, resulting in a smaller radius. Therefore, P3-, with the fewest protons (15), has the largest radius among the given options.

10

Which element has the greatest effective nuclear charge?

Effective nuclear charge increases across a period as the number of protons increases while the shielding effect remains relatively constant.