Video Transcript
How many electrons does aluminum-27 have in its valence electron shell?
This question is asking us to determine the number of electrons found in the valence electron shell of the aluminum-27 isotope. First of all, the valence electron shell is the outermost electron shell of an atom. And the electrons found in this shell are called valence electrons. Let’s first determine the total number of electrons in the aluminum-27 isotope. Then, we can determine the identity of the valence electron shell and finally count up the number of valence electrons that it contains.
The atomic number of aluminum is 13. Therefore, all isotopes of aluminum have 13 positively charged protons. We know that atoms have neutral electric charge because they have an equal number of positively charged protons and negatively charged electrons. Therefore, the aluminum-27 isotope must have 13 electrons.
Now that we know the total number of electrons, we can determine how these electrons fill the electron shells. Let’s use the following table to help us. In all atoms, electrons fill electron shells in order from the lowest energy shell to the highest energy shell. The nucleus of an aluminum-27 atom has 13 protons, and the first and lowest energy electron shell outside of the nucleus is the K-shell. The K-shell can hold a maximum of two electrons. After filling the K-shell, we’re ready to move on to the second lowest energy shell, which is the L-shell. The L-shell can hold a maximum of eight electrons.
We know the aluminum-27 isotope has a total of 13 electrons, and so far we’ve used 10. Therefore, we need to place the last three electrons in the M-shell. We can now see that the M-shell is the valence electron shell of aluminum-27. And the three electrons found in this shell are therefore the valence electrons.
How many electrons does aluminum-27 have in its valence electron shell? The answer is three electrons.
