Question

1.) The atomic number of an element is 11. Based on its electron arrangement, which of the following explains its correct position in the periodic table?

A. Group 1, because it has a single electron in the 4s orbital.
B. Group 3, because it has a single electron in the 3p orbital.
C. Group 1, because its outermost electron is in the 3s orbital.
D. Group 3, because its outermost electron is in the 4p orbital.

Answer 1

The answer is C. And to check, NA which has the atomic number of 11 is in group 1.

Answer 2

The element is in group 1 for having a single electron in the 3s orbital.

Explanation

A neutral atom of element 11 will have a total of 11 electrons. By the Aufbau "build-up" principle, it will have:

• 2 electrons in its 1s orbital,
• 2 electrons in its 2s orbital,
• 6 electrons in its 2p orbital, and
• 1 electron in its 3s orbital.

2 + 2 + 6 + 1 = 11.

Its electron configuration shall be:

1s² 2s² 2p⁶ 3s¹

The first ten electrons $1s^{2} \; 2s^2 \; 2p^{6}$ completes the first two electron shells. That leaves the atom with one valence electron in its 3s orbital. As a result, it shall be placed in group 1 of the periodic table.