Question

An atom has the following electron configuration.

1s22s22p63s23p3

How many valence electrons does this atom have?

3
5
8
15

Answer 1

Answer:

5 electrons

Explanation:

Valence electrons are electrons located in the outermost energy shell, so you want to count the number of electrons in the last energy shell.

You can divide the configuration into 1s2 / 2s22p6 / 3s23p3 to see the energy shells in this atom. There are 3 shells occupied by the atom's electrons, so you need to count the electrons in the third shell as those are its valence electrons.

2 + 3 = 5 valence electrons total

Note: you don't count the 3 before the letter because that only indicates the shell level, not the number of electrons. Count only the exponents.

Answer 2

An atom that has the following electron configuration.

1s22s22p63s23p3 contains only 5 valence electrons in its outermost shell.

Electronic configuration of chemical elements is the classification and ordering of electrons around the nucleus of an atom in reference to their energy levels.

Electrons can be ordered and classified using Aufbau's principle.

Aufbau's principle posits that in the ground state of an atom, electrons are ordered to the subshell of the lowest energy levels before filling the higher energy level subshell.

The valence electron of a chemical element is the outermost electron participating actively in a chemical bonding.

From the given electronic configuration, we will first determine the total atomic number (total electrons) before we determine the valence electrons in the outermost shell.

Given that

1s² 2s² 2p⁶ 3s² 3p³

There are (2 + 2 + 6 + 2 + 3) total electrons in the elctronic configuration.

= 15 total electrons

The maximum number of electrons in the energy levels is determined by using the formula is  $\mathbf{2n^2}$

where;

n = 1, 2, 3 ....

In the first energy level, we have the maximum number of electrons to be:

= 2(1)²

= 2 electrons

In the second energy level, we have:

=  2(2)²

= 2(4) electrons

= 8 electrons

Since we have only 15 electrons, the number of the valence electrons in the atom is:

= 15- (2 + 8 ) electrons

= 15 electrons - 10 electrons

= 5 valence electrons left in the outermost shell.

In conclusion, an atom that has the following electron configuration 1s22s22p63s23p3 contains only 5 valence electrons in its outermost shell.

Learn more about electronic configuration here:

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