Hello chemists welcome back to our chapter
2 lecture series Michele Glass here and our topic for this presentation is the ionic bond. So
we left off in our last video talking about how to determine the chemical behavior of an atom.
And what you do is you look at that valence shell or that outermost electron shell.
Remember if your atom has an incomplete, has unpaired valence electrons, then we would
consider it reactive meaning it can enter into chemical bond. And that could be an ionic bond
which is the topic for this presentation or that could be a covalent bond which we'll talk about
in the next video. When we talk about an ionic bond it's important for us to define what we mean
by ions. So ions are going to be charged atoms. So what we drew in our first video when we
talked about our different atom structure is we talked about uncharged atoms. So now we're
going to be drawing ions. So ions can be either cations or they can be anions. A cation
is going to have a positive charge the only way to become positively
charged is to lose an electron. If you want to you can think about your
plus sign here the t as a plus sign. So you can make it into a plus sign. An anion is going to have a negative charge which means it's going to gain electrons. And so what we're seeing is in the formation
of ions you're going to see an atom will lose an electron or gain an electron. Remember that is
going to be the only subatomic particle that would be involved here. You can't gain or lose protons
because that actually defines that particular element. When we talk about an ionic bond we
can use the memory device transfer electrons because what we see happening is one atom in the
bond is going to gain electrons and the other atom in the bond will lose electrons. And then the key
thing that we see happening here is that opposite charges attract. And so we're going to see that the anion and the negative...the cation and the
negative anion they are in love, right? So they are attracted to each other. So this
is going to be a key feature of the ionic bond. To help yourself remember that your cation he's losing an electron here's this little comic
strip from Frank and Ernest to help you with that. Okay so let's go ahead and use sodium and chlorine
as our examples. We've drawn out sodium before. It has atomic number of 11 and so we're going
to do 11 protons in the nucleus, 11 neutrons, and then we're going to
draw 11 electrons orbiting. Remember two electrons go in the first shell,
eight go in the second, and then because we just have one electron left we have just one electron
here in the valence shell or outermost shell. And let's do the same thing here for our chlorine.
So we can see here that chlorine's atomic number is 17, so 17 protons, 17 neutrons, and
then let's fill in our electron shells. Remember to draw them first
unpaired and go back in and pair. And when you get your chlorine drawing complete notice that you have unpaired electrons in the valence shell. So
when we have unpaired valence electrons or an incomplete valence shell then we have reactive
atoms. And reactive atoms are going to do some kind of chemical bond in order to complete that
outermost shell. What happens in an ionic bond is one atom will lose an electron and the
other atom will gain an electron. So that electron that used to belong to sodium now belongs
to chlorine. And then your sodium is now called a cation notice that it has more positive protons
compared to the number of electrons. There are 11 positive protons and just 10 negative electrons
so we're going to assign a positive charge to sodium. And over here when we look at chlorine
we are seeing an anion it has gained an electron. So in this case this atom has 17 positive protons
and 18 negative electrons so because it has more electrons compared to the number of protons it
is called an anion and it has a negative charge. If we get back up here to our descriptions of
cations and anions we can add here that your anion will typically be assigned an "-ide" ending. So
when we go back and we look at this compound here we can write sodium chloride like this (Na+Cl-).
So ionic bonds you're always going to see the charges. These are fully charged atoms.
We write the anion excuse me the cation first and then the anion second and we give it an
"-ide" ending so chlorine becomes called chloride. Now what is it that's actually holding the sodium
and the chloride together? That is actually just this attraction between charges. So we see
that opposite charges attract in chemistry and here's a funny little comic to help us
remember. It says "Perhaps one of you gentlemen would mind telling me just what it is outside
the window that you all find so attractive?" Right? And notice that you've got cations in
the classroom and anions outside. That's it for ionic bonds. Stay tuned for covalent and as
always take care of yourselves and each other.