So first, let's take a look at general atomic structure.
We have protons, neutrons, electrons.
You've probably all heard of those.
To review protons and neutrons,
they're found in the nucleus of an atom.
And electrons are found in the periphery.
Protons and neutrons have some mass.
And electrons have barely any mass at all,
which is why they float around essentially in electron cloud
around the central nucleus of protons and neutrons.
Protons are found in the nucleus. They're positively charged
and they weigh one atomic mass unit.
Neutrons are also found in the nucleus
and weigh one atomic mass unit
whereas electrons weigh barely anything.
Their weight is essentially negligible.
And they're found in a cloud surrounding the protons and neutrons
in the nucleus and have a negative charge.
So proton's positive, electron's negative, neutrons neutral.
Atomic number is what defines an element.
So let's say we're looking at carbon, it has atomic number 6.
It means it has 6 protons.
And any atom with 6 protons is called carbon.
We may see some variants in the number of neutrons and electrons,
we'll take a look at some example shortly.
But atomic number definitely defined by the number of protons
and that defines what the element is called.
We have also atomic mass. When we add the protons and the neutrons
in the nucleus together, that gives us the atomic mass.
Again, each of them is one atomic mass unit,
and thus our atomic mass for standard carbon,
the most prevelant form of carbon is 12 atomic mass units.
As I mentioned, we could have a varying number of neutrons.
They are less common forms.
But isotopes are the name we gave for
a varying numbers of neutrons.
Again, here we have carbon. It has 6 protons.
It will always have 6 protons.
But we could have carbon-13, which you've probably
heard of in carbon dating. Carbon-14.
We have 6 protons. We subtract that from 13
means we have 7 neutrons.
We might even see in variant instances, carbon-14, in which case
we actually have 8 neutrons and the atomic mass of 14.
We can also see variation in electrons.
When we have either more or less electrons, we have ions.
For example, if we look at sodium, in its natural state,
we have a balanced number of electrons and protons.
However, we'll often see sodium as a postive ion, so Na+,
in which case we have one less electron
We take away a negative charge,
but we still have the same number of positive charges,
so we end up with a positive ion.
In the example below we see, we have chlorine.
Chlorine is in its balanced state
where we have equal number of electrons and protons.
However chlorine sometimes likes to gain an electon,
in which case we have an additional negative charge
and so there's not balance, we'll see Cl-.
And we'll see later in the next lecture,
how sodium and chloride might interact with each other
because of these positive and negative charges.
So once again, to emphasize,
proton number is not going to change, at least in biology.
And proton number is going to define
what element we're looking at.