Video Transcript
An uncharged atom has an atomic
number of six and a mass number of 11. How many protons does that atom
have? How many neutrons does that atom
have? And how many electrons does that
atom have?
So to make sure we don’t miss
anything out, let’s underline all the important bits of the question. So what we’ve got is an uncharged
atom. This part is really easy to
miss. We also know that it’s got an
atomic number of six and a mass number of 11. But, what do we mean by atomic
number and mass number?
Atomic number is defined as the
number of protons in a nucleus. And mass number is defined as the
number of nucleons, that’s protons and neutrons, in a nucleus. By the way, protons and neutrons
are called nucleons because you find them in the nucleus of an atom. So based on that, we’ve got enough
information to answer our question.
First of all, how many protons does
that atom have? Well, we know that it’s got an
atomic number of six. And the atomic number is just the
number of protons. So these two numbers are
identical. It has six protons.
Secondly, how many neutrons does
that atom have? Well, we’ve got the mass number and
we’ve got the atomic number. Now the mass number is the total
number of nucleons. That’s protons and neutrons put
together. And that total number is 11. But we know that out of those 11,
six of them are protons. So the remaining number are
neutrons. So in order to find that out, what
we need to do, is to do 11 minus six. And that ends up being five. So we’ve got five neutrons. And that does make sense. If we’ve got six protons and five
neutrons, then together we’ve got 11 nucleons. That’s protons and neutrons
together. And hence, the mass number is
11.
Finally, we need to work out how
many electrons that atom has. Now in order to answer this, we
need to look at the very first piece of information that we’ve been given in this
question. The fact that the atom is
uncharged. If the atom is uncharged, then the
total overall charge of the atom is zero. That’s what uncharged means. So in order to do that, all of the
positive charges in the atom have to be cancelled by all of the negative
charges. Or, in other words, the number of
negative charges in the atom has to be exactly the same as the number of positive
charges in the atom. That way, each of those negative
charges can cancel out each one of those positive charges. So we know that we’ve got six
protons in the atom. And those protons are positively
charged. Therefore, we’ve got six positive
charges in the atom. We also know that electrons are
negatively charged. So it’s the electrons that’ll be
cancelling out all other protons. Hence, the number of electrons has
to be the same as the number of protons. So we’ve got six electrons in the
atom. And that’s the final answer to our
question.
