Question

the ground state electron configuration of an al atom is
answer:
a $1s^{2}2s^{2}2p^{6}3s^{2}3d^{1}$
b $1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$
c $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}4p^{1}$
d $1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}$
e $1s^{2}2s^{2}2p^{1}$

Explanation:

Step1: Determine the atomic number of Al

Al (aluminum) has an atomic number \(Z = 13\). This means it has 13 electrons in the ground - state.

Step2: Fill the orbitals according to the Aufbau principle

• Fill the \(1s\) orbital first: \(1s\) can hold 2 electrons, so we have \(1s^{2}\).
• Then fill the \(2s\) orbital: \(2s\) can hold 2 electrons, so now we have \(1s^{2}2s^{2}\).
• Next, fill the \(2p\) orbital: \(2p\) can hold 6 electrons, so we get \(1s^{2}2s^{2}2p^{6}\).
• After that, fill the \(3s\) orbital: \(3s\) can hold 2 electrons, resulting in \(1s^{2}2s^{2}2p^{6}3s^{2}\).
• Finally, we need to place the remaining \(13-(2 + 2+6 + 2)=1\) electron. According to the Aufbau principle, the next orbital is \(3p\), so the electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}\).

• Option A: \(1s^{2}2s^{2}2p^{6}3s^{2}3d^{1}\) is incorrect because the \(3p\) orbital should be filled before the \(3d\) orbital according to the Aufbau principle (\(E(3p)<E(3d)\)).
• Option C: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}4p^{1}\) is incorrect. The total number of electrons in this configuration is \(2 + 2+6 + 2+6 + 2+1=21\), which is not equal to the number of electrons in Al (\(Z = 13\)).
• Option D: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}\) has \(2 + 2+6 + 2+2 = 14\) electrons, which is more than the number of electrons in Al.
• Option E: \(1s^{2}2s^{2}2p^{1}\) has \(2 + 2+1=5\) electrons, which is less than the number of electrons in Al.

Answer:

B. \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}\)