# Question Video: Identify Elements from Atom Diagrams Physics

The diagram shows electrons in different electron shells in an atom. The atom is electrically neutral. What element is this an atom of?

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### 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?

Okay, so in this question, we’ve been given a diagram, which shows what appears to be the nucleus at the centre of the atom as well as the electronic energy levels, which are represented in black. Now, these electronic energy levels are also known as shells. And we can see that occupying these shells there are one, two, three blue dots representing electrons. In other words, there’re three electrons in this atom.

Now, we’ve been told that this atom in question is electrically neutral. This means that the overall electric charge on the atom is zero, because it’s neutral. Now, to understand the significance of this, we should recall that electrons are negatively charged particles. And that atoms are neutral if the number of electrons in the atom is equal to the number of positively charged protons found in the nucleus. And so what this diagram is telling us is that there are three electrons in this atom. And in order for it to be neutral, there must be three protons in the nucleus of the atom. And then, we can recall that an element is defined by the number of protons found in the nucleus of an atom of that element.

And so in order to find the answer to our question, we will need to look on the periodic table. Specifically, we can recall that the periodic table of the elements shows all of the elements arranged in order of atomic number, where the atomic number of an atom is simply the number of protons found in the nucleus of that atom. And so considering the periodic table is arranged in order of increasing atomic number, we want to find the element in the periodic table, which has an atomic number of three. Because there are three protons in this particular atom’s nucleus. So the element that has three protons in its nucleus is lithium. And hence, that is the answer to our question.

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