Combining Elements
How Chemical Compounds Are Made
Combining Elements
• Elements can exist on their own but most
matter consists of two or more elements
combined together
• How do they combine??
Metals and Non-metals
• Metals have a tendency to lose electrons and
form positive (+) ions.
• Non-metals tend to gain electrons and form
negative (-) ions
• Positive and negative charges attract
• When a positive ion and a negative ion bind
together they form an ionic bond
What makes an Atom Stable?
• First of all, what does “stable” even mean?
– Answer: A stable atom is one that will stay the
way it is. It will not gain or lose any of its
components (protons, neutrons or electrons)
• Atoms are stable if their outer orbital is full of
electrons!
What Makes An Atom Stable?
Example – Helium
An atom of Helium only has one orbital and this
orbittal has two electrons. Since the first orbital can
only hold two electrons, the orbital is full.
That means that helium is stable.
Unstable Atoms
• Example: Sodium
Sodium has 11 electrons; 2 in the first orbital,
8 in the second and 1 in the third.
It’s outer orbital is not full since it
only has one electron.
So How Can It Become Stable?
The easiest way for it to become stable is for the
one electron to leave.
Making an Unstable Atom Stable
• If Sodium loses an electron it will be stable
(and happy !!!)
Just one problem
If an atom does not have
The same number of protons
and electrons then it is not an
atom
Making an Atom Stable
• But this isn’t really a problem
All we have to do is change its
name. So we don’t call it an atom
Anymore. We call it an Ion!
An ion is an atom that has gained or lost electrons. Since Sodium
has lost an electron (which is negative) it becomes a positive
ion
Example (Sodium and Fluorine)
• An atom of Sodium has a single electron in its
outer orbittal. This makes it unstable
• An atom of fluorine has seven electrons in its
outer orbital. It needs one more to be stable.
Metal and Non-Metal
• So they make a deal!
• The sodium gives an electron to fluorine
• Now they’re both happy
• The only thing is:
– They’re not atoms any more
• They’re IONS
• An ion is like an atom but it has a charge
• Now REMEMBER
– Opposites attract!
Ionic Compounds
• So sodium and fluorine are attracted to each
other and form an inseparable bond
And they call themselves
Sodium Fluoride!! (or NaF)
Sodium Fluoride is an Ionic Compound
Ionic Compounds
Here’s another example:
• Let’s take Calcium and Chlorine
• Calcium needs to get rid of two electrons to be stable
but Chlorine only needs one.
• SO WHAT CAN THEY DO?
Building Ionic Compounds
• What if Chlorine found a friend?
• Another chlorine atom!
Making Ionic Compounds
• Now Calcium can give one electron to each of
them!
• Now everyone’s happy!
Making Ionic Compounds
• This compound is called Calcium Chloride
• Or CaCl2
• Because there is one calcium ion and
two chlorine atoms
Making Ionic Compounds
• Making ionic compounds is easy if you follow
a few rules
1.
Write down the name (or symbol) of each element starting with the
metal
e.g. Potassium (K)
Sulfur (S)
2. Beside each one, write down the number of electrons that the element
needs (or has to give away) to be stable
K (1)
S (2)
3. Now criss cross the numbers
K (1)
S (2)
Making Ionic Compounds
• This gives us
• Try these
Metal
Non-metal
Magnesium Nitrogen
Lithium
Chlorine
Calcium
Carbon
Aluminum
Silicon
K2S
or
Potassium Sulfide
Metal
Non-metal
Final
Symbol &
Element
Formula
Electrons to
and
(Criss cross)
lose
Electrons to
gain
Mg (2)
N (3)
Mg3N2
• One last thing
– If you can divide both numbers by a highest
common factor: DO IT!!
–Example: Calcium Oxide
Ca2O2
• 2 and 2 are both divisible by 2 so
• Ca2O4 becomes CaO
Naming Binary Ionic Compounds
• A binary ionic compound is an ionic compound
with two elements.
• They’re very easy to name.
1. Write down the metal first, then the non-metal.
2. The metal keeps its name.
3. Now take the non-metal, write down its first
syllable and then write ide.
4. That’s it! You’re done!
Naming Binary Ionic Compounds
• Example
• Mg3P2
• Magnesium Phosphide
Now try these
Formula
Na2O
AlCl3
Be3S2
Name
More Practice
Try these (Name
Compound
Calcium Chloride
Beryllium Phosphide
Aluminum Oxide
Potassium Nitride
Magnesium Carbide
Sodium Iodide
Lithium Sulfide
Symbols and
“Criss-Cross”
Formula)
Formula
Now Try These
(Formula
Formula
CaF2
Al4Si3
Mg3P2
BeI2
LiF
Ca2C
Na3P
Name)
Name