2. Ionic Bonds
Fairly straightforward:
• The Atom with the higher electronegativity steals an electron from the atom with
(much) lower electronegativity.
• They are then bound by the electric force (which is really strong).
• Typically form from elements on opposite sides of the periodic table.
Think of it as the bully stealing lunch money from the little kid who then follows him
around begging for it back.
3. More on Ionic Bonds
• Must have charges balanced
• May be more complex than
NaCl –
– CaF2
– Al2O3
It all depends on how many
electrons each is capable of
giving up/receiving.
• Crystal shape determined by
interactions
– break a salt crystal and the
shards will tend to have the
same shape
4. Covalent Bonds
• Both atoms want one* more electron
• Solve problem by sharing (neither is strong enough to take it
from the other)
Imagine two kids playing with (sharing) the same toy.
*sometimes more than one, but in this picture only one.
5. Polar Covalent Bonds
Unequal sharing.
• Atom with larger electronegativity has a partial negative charge.
• Atom with smaller electronegativity has partial positive charge.
• Electrons are still shared, but spend more time around larger
electronegativity atom.
6. Bonding is a spectrum
Bully – Ionic
Total transfer
Unequal sharing –
Polar Covalent
Shared, but spends
more time on one side.
Equal Sharing –
Covalent
7. • Imagine a tug of war – if one side has the strength to
win the molecule will be polar.
Polar Molecules:
Electronic Tug-of-war
9. Metallic Bonds
• Metals have a very weak hold on outer electrons
• In a lump of metal, these outer electrons escape
• Resulting metal ions stabilized by a ‘sea’ of free electrons
(This is why metals can mix into alloys so well – metal ions,
regardless of type, stabilized in a sea of electrons.)
10. Chemical Equations
The general form of a chemical equation:
reactants → products
A specific example:
C(s) + O2(g)→ CO2(g)
11. A simple rule for all chemical
equations:
Law of Mass Conservation:
Matter is neither created nor destroyed.
What this means:
There must be the same number of each type of
atom on each side of a chemical equation.
12. Two more rules:
• You cannot change the identity of a substance.
– Changing H2O to H2O2 is not allowed.
The first is water the second is hydrogen peroxide, a poison
when pure.
You may change the number in front of a chemical. It
multiplies the number of atoms of each type you have.
For instance H2O changed to 2 H2O. First case has 2 hydrogen
and one oxygen, second has 4 hydrogen and two oxygen.
13. Our first example was easy, it was balanced from the
start.
Things don’t always work out nicely:
H2(g) + O2(g) -> H2O(l)
Remember our rules: What is wrong with this?
• It has more oxygens on left than right!
14. +
H2
O2 H2O
Let’s try to fix this. First, let’s make the right hand side have the same amount of
oxygen as the left.
+
H2
O2 2H2O
We’re getting somewhere, but now we have more
hydrogen on right than left.
15. Balance at last!
• 4 hydrogen atoms on left and 4 on the right.
• 2 oxygens atoms on left and two on the right.
Good!
So is there some procedure we can follow?
+
2H2
O2 2H2O
17. Suggested Procedure
1) Always balance one element at a time. Start
with the most complex reactant.
2) If you unbalance previously balanced
elements don’t worry about it now.
3) After each element is done, then go back and
fix previous ones.
4) Repeat step 3...
5) Minimize coefficients if necessary (you may
get 2:4:2 – reduce to 1:2:1).
21. Review
• Bonding is a spectrum
– most polar is ionic – total electron transfer (NaCl)
– next is polar covalent, the electron is shared unequally (HF)
– finally nonpolar covalent where the electron is equally
shared. (N2)
• The structure of a metal is one of metallic ion islands
in an electronic sea.
• In a chemical reaction mass is neither created nor
destroyed.
• Must have same number of each type of atom on
each side of a chemical equation – balanced!
