CHAPTER 5
IONIC COMPOUNDS
Mrs. Czyryca
What you already know:
 Ionic compounds donate and accept electrons,
not share, in order to become stable.
Ionic compounds consist of a metal and a
nonmetal.
An atom that has lost an electron has a
positive charge.
An atom that has gained an electron has a
negative charge.
Remember my joke?
Two atoms were walking down the street.
Looking all around, one says, “Oh my gosh,
I lost an electron!”
The other says, “Are you sure?!”
The first says, “I’m POSITIVE!”
You should also remember:
When a compound forms and it’s atoms
become stable, energy is given off.
And that’s EXOTHERMIC!
We are using a new unit for ionic
compounds
Instead of using atoms, molecules,
particles, or ions as a unit---we will use
FORMULA UNITS
Formula units are the smallest collection of
an ionic compound
For example:
Instead of writing:
6.022 x 1023molecules NaCl
Write:
6.022 x 1023 formula units NaCl
Formation of KCl from it’s elements
As you can see from the prior slide, KCl
doesn’t exist as a molecule.
There are many, many K and Cl atoms
bonded into a structure called the
CRYSTAL LATTICE.
The gaseous chlorine, Cl2, exists as
individual molecules.
The metal, potassium atoms, K, just pile
up like oranges at the grocery store.
Look again…
Let’s look individually at the potassium
and chlorine atoms.
K is in group 1 on the periodic table…
So what is it’s charge likely to be once it
loses an electron to become stable?
+1
Chlorine is in group 17
 What charge would chlorine have once it
gains an electron in order to become
stable?
-1
What are the positive ions called?
Cations
That’s pronounced “cat” – “ion”
What are the negative ions called?
Anions
That’s pronounced “an” – “ion”
not ant ion, an’ ion!
We know a positive with a negative
=zero
That’s electroneutrality!
when the charges equal zero
+1 -1 = 0
(can I use a calculator?)
How many cations and anions are
present in MgCl2?
MgCl2?
Just one cation.
And two anions
How many cations and anions are
present in MgCO3?
MgCO3?
Just one cation still.
And one anion- carbonate
One more…
How many cations and anions are
present in Mg3(PO4)2?
Mg3(PO4)2?
Three cations.
And two anions- two phosphate
polyatomic anions
Potassium’s electron configuration:
1s22s22p63s23p64s1
It loses that electron in the 4s orbital to
become stable.
It then has the same electron configuration
as a noble gas. VERY STABLE!
ISOELECTRONIC
having the same electron configuration as
another element
The potassium ion is isoelectronic with
Argon.
1s22s22p63s23p6
chlorine’s electron configuration:
1s22s22p63s23p5
It gains an electron in the 3p orbital to
become stable.
It then has the same electron configuration
as a noble gas. VERY STABLE!
ISOELECTRONIC
having the same electron configuration as
another element
The chlorine ion is also isoelectronic with
Argon.
1s22s22p63s23p6
Naming ions (atoms with a charge)
Like any cation, the potassium keeps it’s
name and you add the word “ion” to the
end.
“Potassium ion”
Not too tricky, huh?
Naming ions (atoms with a charge)
Like any anion, the end of chlorine
changes to “ide”
and you add the word “ion” to the end.
Chloride ion
What does a roman numeral tell us?
The charge on the cation
Never an option for the anion b/c it
only has one possible charge
EVER!