Question

1. according to the aufbau principle, electrons fill orbitals in which order?

a) randomly
b) based on increasing principal quantum number
c) based on increasing energy levels
d) based on decreasing energy levels

1. hunds rule states that electrons prefer to occupy degenerate orbitals:

a) singly with parallel spins
b) singly with opposite spins
c) in pairs with parallel spins
d) in pairs with opposite spins

1. which of the following elements demonstrates a deviation from expected electronic configuration due to stability gained from half - filled or fully - filled subshells?

a) sodium (na)
b) chromium (cr)
c) magnesium (mg)
d) nickel (ni)

1. the periodic trend in atomic radius across a period can be attributed to:

a) decreasing nuclear charge
b) increasing electron shielding
c) increasing number of protons
d) decreasing number of valence electrons

1. ionization energy tends to increase across a period due to:

a) decreased nuclear charge
b) increased atomic radius
c) increased electron affinity
d) increased effective nuclear charge

Explanation:

1. The Aufbau Principle states that electrons fill orbitals starting from the lowest - energy orbital. So, electrons fill orbitals based on increasing energy levels.
2. Hund's Rule states that electrons prefer to occupy degenerate orbitals singly with parallel spins to minimize electron - electron repulsion.
3. Chromium (\(Cr\)) has an electron configuration of \([Ar]3d^{5}4s^{1}\) instead of the expected \([Ar]3d^{4}4s^{2}\) because a half - filled \(d\) - subshell (\(d^{5}\)) gives extra stability.
4. Across a period, the number of protons (nuclear charge) increases. The electrons are added to the same principal energy level. The increased nuclear charge pulls the electrons closer, resulting in a decrease in atomic radius.
5. Ionization energy is the energy required to remove an electron from an atom. Across a period, the effective nuclear charge (the net positive charge experienced by an electron) increases. This stronger attraction between the nucleus and the electrons makes it more difficult to remove an electron, so ionization energy increases.

Answer:

1. C. Based on increasing energy levels
2. A. Singly with parallel spins
3. B. Chromium (Cr)
4. C. Increasing number of protons
5. D. Increased effective nuclear charge