Video Transcript
The diagram shows electrons in different electron shells in an atom. The atom is electrically neutral. What element is this an atom of?
We’ve got this diagram here that we’re told shows an atom with electrons in different electron shells. This red circle that we can see at the center of the diagram represents the nucleus of the atom, and this is where all of the atoms, protons, and neutrons are found. Then, around this nucleus, we can see that we’ve got these two black rings, and these represent the first two electron shells of the atom.
These electron shells, which are also known as the atom’s energy levels, are where the electrons of the atom are found. These electrons are represented by the small blue circles drawn on each of the rings. The shell that’s closest to the nucleus — so that’s the one that’s represented by this black ring here in our diagram — is known as the first electron shell or the first energy level. Then, the next shell out from this — so that’s the one represented by this ring in our diagram — is the second electron shell or energy level.
If the atom also had electrons in higher electron shells, then the next one out would be the third shell and then we’d have the fourth shell, and so on. However, when we draw a diagram of an atom, we generally only draw the electron shells that have at least one electron in them. So, in this case, that’s just the first two shells.
The question is asking us to identify what element this is an atom of. We’re told that the atom is electrically neutral, and this means that it has no overall electrical charge. We can recall that the charge of an electron and the charge of a proton are equal in magnitude but opposite in sign. Protons are positively charged, while electrons are negatively charged. In order for an atom to be electrically neutral, the number of negatively charged electrons must be equal to the number of positively charged protons because then the negative charges and the positive charges exactly cancel each other out, leaving the atom with no overall electrical charge.
Now, we might be wondering why this information about the number of electrons and the number of protons in a neutral atom is useful to us for this question. Well, we’re asked to identify what element this atom in the diagram is an atom of. And we can recall that this element is determined by the atom’s atomic number, which is equal to the number of protons in the atom’s nucleus.
In the diagram we’re given in this question, we can’t see directly how many protons there are in the nucleus because this nucleus is just drawn as a single red circle. However, what we can do is to count up all of the electrons that are drawn on the shells around this nucleus. And then since we know that for an electrically neutral atom the number of electrons is equal to the number of protons in the nucleus, then the number of electrons that we count will give us the atomic number of the atom, which will allow us to work out what element it’s an atom of.
To count the electrons in this atom, let’s number off the blue circles drawn on each of the black rings in the diagram. We can see that on the inner ring or the first electron shell, there are two electrons. And then on the outer ring, which represents the second electron shell, there are four electrons. So then, the total number of electrons in the atom is equal to the two electrons from the first shell plus the four electrons from the second shell, which works out as a total of six. Since the electrically neutral atom has six electrons, then this means that it must also have six protons. So then, we know that the atomic number of the atom is equal to six.
Then, at this point, we can either recall or look up in a periodic table that this corresponds to the element carbon. So then, our answer to this question is that the atom that’s shown to us in the diagram is an atom of the element carbon.
