Hello and welcome to bonding part 1, ionic bonds and the resulting ionic
compounds, in which we will take a look at how ions form, what forms the ionic bond,
balancing charge in ionic formulas, and looking at how the ionic bond
relates to the structure of ionic compounds.
Let's start with a question:
Why do atoms stick together?
In the ionic bond neutral atoms lose or gain
electrons to get a stable electron configuration, which is often the outer
octet of a noble gas. Fluorine has 7 valence electrons shown as dots around
the symbol, and so gaining one more gives it an octet.
And sodium losing its lone valence electron
allows the octet below that outer electron to become
valence electrons. Once that electron exchange happens the
result is a positive sodium ion and a negative fluoride ion.
The ions are attracted to each other
due to having opposite charge. The compound sodium fluoride
consists of sodium ions and fluoride ions. I hope you can see here
what the ionic bond is. Yes you're right! The ionic bond is the electrostatic
attraction between the positive sodium ion and the negative fluoride ion.
One thing that is essential to know and remember is that ionic compounds are neutral.
The amount of positive charge and negative charge has to be equal,
so that they cancel each other, creating a neutral compound. Here are the 1+ and
1- charges cancel each other, sodium fluoride is neutral. What about
ionic compounds made of ions where the charge does not balance such as the
magnesium ion with a 2+ charge and the 1- fluoride. What can we do to
fix this and make it neutral? We simply add more ions until it balances.
The charges of two fluoride ions balanced the charge on a single magnesium ion.
2+ balances 2-, and the formula MgF2 gives us a neutral compound.
Typically ionic bonds form from metals bonded to nonmetals. You can identify an
ionic compound by seeing that is composed of a metal and a nonmetal,
and this is because metals form cations (positive ions), and nonmetals form
anions (negative ions). On the periodic table we can distinguish metals and
nonmetals by their location on the table. metals and nonmetals are divided by the
stair-step line seen here in yellow, and metals are to the left of the stair-step
in blue, nonmetals are to the right in brown, with metaloids along the
stair-step in violet. Let's take a closer look at the atomic structure to see why
ions form and how that influences the structure of the ionic compound.
Neutral sodium has a single valence electron but we can see that there is an octet just
below that valence electron, while neutral fluorine only needs one more
electron to gain an octet. The reaction here is the exchange of sodium's valence electron.
Sodium loses its valence shell and become smaller while fluorine
experiences more repulsions with the added electron and becomes larger.
Both ions now have the stable electron configuration of neon with 10 total electrons.
Let's back up a bit. Neutral sodium has 11 electrons and 11 protons,
while neutral fluorine has 9 electrons and 9 protons. The electron
exchange allows each atom to now have the 10 electrons of the neon electron configuration.
In showing the reaction and the two models side-by-side, we can
more easily see how the ionic bond forms, which is the electrostatic attraction
between positive and negative charge. To get a better understanding of the
structure of ionic compounds, let's view the atoms and ions as simple spheres.
The ionic compound does not exist as a diatomic molecule as implied here, but as
an ongoing array of alternating positive and negative charge, the organization of
which is partly determined by the size and charge of each ion. With magnesium
fluoride you can see more readily the importance of ion size and ratio,
two fluorides for every one magnesium, on how the ions stack in the very ordered crystalline structure.
That's it!
This has been a mad scientist production!
SEEYA!