Today we're going to discuss the formation of ions
and then, this is going to flow into how we make
ionic compounds. So the first thing we need to understand about
atoms, is that they have a specific number of
valence electrons. Valence electrons are the electrons
that are on the outermost energy level, and we can tell
the number of electrons in the representative group,
atoms, by their group number. So
the representative groups are the groups that have an A; so, 1A through 8A.
Group 1A has 1 valence electron;
group 2A has 2; 3A has 3;
4A has 4. I'm sure you're seeing the pattern by now,
all the way to 8A, and they have
8 valence electrons, OK. 8 valence electrons is the maximum number of
electrons
that you can have; that is basically a full set,
which we call an octet, OK. So, the noble gases, which are
which is the common name for the group A elements, have a full set
of valence electrons. This is the most stable electron configuration, to have a
full set.
All of the other elements want to be like a noble gas, and want to
achieve an octet, OK. So
they're going to gain or lose
electrons so that they reach 8 valence electrons.
So, when we talk about
ions, ions are
atoms that do not have an equal number of protons
and electrons, OK. If they're equal, they would be neutral;
an ion has an unequal number, so they're either going to be positively
charged or negatively charged,
OK. So ions, for example, group 1A,
OK, if we use sodium for as an example of a group 1A
element; sodium has 11 protons
and 11
neutrons in a normal neutral atom.
Sodium is going to lose
its 1 valence electron, so that it looks like the noble gas
that precedes it. When it does this, it loses
1 electron; it's still going to have 11 protons,
but now (that's electrons)
its going to have 10 electrons, OK.
Now it is not neutral anymore, it
has 1 extra positive charge versus negative charge;
so now this would be sodium with a positive charge, +1.
So, every element that's in group 1A is going to do the same thing, they're going
to lose their 1
valence electron and it's going to give them
a +1 charge. Group 2A
is going to do something very similar, so it's
plus one for 1A. Group 2A: if we look at magnesium as an example;
12 protons, 12 electrons,
it's neutral. It wants to look like a noble gas;
it's going to lose its 2 valence electrons,
2 electrons leave.
We still have 12 protons, but now we only have 10
electrons, OK. Since there are 2 more positives than negatives, it has a +2
charge,
and we would write the symbol as magnesium (Mg)
2+. Everything in group 2A is going to do the same thing, they're going to lose
their 2
valence electrons and form a 2+ ion.
Same pattern for group 3A,
OK, and it's going to form +3 charge.
Group 4A doesn't follow the pattern,
OK. In group 4A, the elements are
(mostly) nonmetals, OK. Nonmetals
that have 4 valence electrons, the
upper ones, aren't going to form ions;
so, they would either have to lose
4 electrons or they would have to gain 4 electrons and that's too much
energy involved, so normally we're not going to see
ions here. Some of the transition metals will
form +4 charges, but
that doesn't apply to all of these, so we're going to just
kinda put an X here and skip over that.
Now the nonmetals: starting group 5A over on this side;
if we followed this same pattern, they would have to lose
5 electrons to get to 8 valence electrons.
Or, the easier way would be to gain
three, OK? So it's easier for these guys to gain 3
electrons to reach 8. So, if we have something like
nitrogen;
nitrogen, for example, has 7
protons, 7
electrons, OK. In this case,
to form an ion, it's going to gain, we're going to
add 3
electrons. When we do that we still have 7 protons; it's still nitrogen,
but now we have 10
electrons. This is going to give us a full set; it's going to look like the noble gas,
neon, which has 10 electrons.
So, now we have more negatives than positives;
so we have a -3 charge
and you'd write the symbol like this. So, the nonmetals that are in Group 5A are
all going to do the same thing and are all going to have
a -3 charge because they're going to gain 3 electrons.
Group 6A: oxygen, for example,
oxygen has
8 protons, 8 electrons.
It's nearest noble gas, what it wants to look like, is neon, which has 10
electrons, so we're going to gain 2 electrons.
So, 8 protons, 10 electrons:
its going to have a -2 charge
because it has 2 extra electrons, so everything, all of the non metals in group
8A,
I'm sorry, 6A are going to do the same thing, and have a
-2 charge. Group 7A: 7 valence electrons,
they need to gain 1 more to look like the nearest noble gas;
so they're going to have 1 extra electron; they're going have a
-1 charge.
Group 8A: they already have a full set of electrons, so they're not going to gain or
lose,
so we're not going to form any ions for group 8A.
OK, now that you understand how the ions are formed,
we can take this information and start making ionic compounds.