Question

the electron configurations described in this chapter all refer to gaseous atoms in their ground states. an atom may absorb a quantum of energy and promote one of its electrons to a higher-energy orbital. when this happens, we say that the atom is in an excited state. the electron configurations of some excited atoms are given. select the configuration that would correspond to an excited state of as.
○ $1s^1 2s^1$
○ $1s^2 2s^2 2p^2 3d^1$
○ $1s^2 2s^2 2p^6 4s^1$
○ $\text{ar} 4s^1 3d^{10} 4p^4$
○ $\text{ne} 3s^2 3p^4 3d^1$

Explanation:

1. First, determine the ground - state electron configuration of As (Arsenic). The atomic number of As is 33. The electron configuration of Ar (Argon) is $[Ar]=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{3}$. So the ground - state electron configuration of As is $[Ar]4s^{2}3d^{10}4p^{3}$.
2. For an excited state, an electron is promoted from a lower - energy orbital to a higher - energy orbital.

• Option 1: $1s^{1}2s^{1}$ has only 2 electrons, while As has 33 electrons. So this is not for As.
• Option 2: $1s^{2}2s^{2}2p^{2}3d^{1}$ has a small number of electrons (2 + 2+2 + 1=7) and does not match the electron count of As.
• Option 3: $1s^{2}2s^{2}2p^{6}4s^{1}$ has 2+2 + 6+1 = 11 electrons, not 33.
• Option 4: The ground - state configuration of As is $[Ar]4s^{2}3d^{10}4p^{3}$. In the configuration $[Ar]4s^{1}3d^{10}4p^{4}$, an electron from the $4s$ orbital (lower energy) is promoted to the $4p$ orbital (higher energy). The total number of electrons is $18+1 + 10+4=33$, which matches the number of electrons in As.
• Option 5: $[Ne]3s^{2}3p^{4}3d^{1}$ has $10 + 2+4 + 1=17$ electrons, not 33.

Answer:

[Ar] $4s^{1}3d^{10}4p^{4}$ (the option with this electron configuration)