Question Video: Identifying Electron Shell Structure for an Oxygen Atom | Nagwa Question Video: Identifying Electron Shell Structure for an Oxygen Atom | Nagwa

# Question Video: Identifying Electron Shell Structure for an Oxygen Atom Chemistry

Which picture shows the arrangement of electrons in an atom of oxygen? [A] Picture A [B] Picture B [C] Picture C [D] Picture D [E] Picture E

03:20

### Video Transcript

Which picture shows the arrangement of electrons in an atom of oxygen?

What we’ve been given are five electron shell diagrams. In the middle is a drawing of a nucleus, much, much bigger in relation to the atom than it would be in real life. The red circles with p are protons, and the white circles with n are neutrons. The black circles are electron shells, which can fit a limited number of electrons. And the blue dots are the electrons.

What the question is asking for is the picture that shows the arrangement of electrons in an atom of oxygen. Oxygen is an element that we can find on the periodic table. There, we see that the atomic number of oxygen is eight. This means that every atom or ion of oxygen has eight protons in its nucleus. Atoms are neutral, which means we need an equal number of electrons and protons. The first thing we can do is check all of our diagrams depict eight protons and eight electrons.

All the nuclei look identical, and they each have eight protons. This means we’re dealing with nuclei of oxygen, and we can proceed to the next test. The easiest way to count out electrons is to work out the electron configuration of each diagram. We do this by counting the electrons in each shell, starting with the first shell.

In the first diagram, there are two electrons in the first electron shell, there are two in the second, and there are four in the third. This is the right number of electrons, but we’ll come back to this in a moment. The second diagram has configuration two, six. And the third diagram has configuration zero, eight. Remember, the zero still matters because it’s an inner shell. The fourth diagram has configuration eight. And the last diagram has configuration four, four.

Each electron shell has a fixed maximum number of electrons that it can fit. You can fit two electrons in the first electron shell and up to eight in the second. The other principle we’re going to use to find the answer is that electrons occupy the most stable space. For electron shell diagrams, that means the lowest available shell.

So, in the first diagram, we can see that there are two electrons in the lowest available shell. That’s good. However, there are four electrons in the third shell when there’s still space in the second. So, this is not the correct diagram. In the second diagram, there are again two electrons in the first electron shell. And the remaining six out of the eight electrons fill the second shell as they should. So, this is the correct diagram. But let’s look at the other three just in case.

In the third diagram, there are eight electrons in the second shell when there are two available spaces in the first. So, this is not the correct configuration. For the fourth diagram, all the electrons in the first electron shell, which is six too many. And in the last diagram, there are two too many electrons in the first electron shell. Meaning that the picture that shows the correct arrangement of electrons in an atom of oxygen is the one with eight protons in the nucleus, two electrons in the first shell, and six in the second.

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