CHEMICAL BONDING
THERE ARE TWO KINDS OF PURE
SUBSTANCES
Elements
Compounds
Let’s start the new notes…
Elements

Substance that cannot be separated
or broken down into simpler
substances by chemical means.
Ex’s- any box on the periodic table

Made of only 1 type of

atom
The smallest unit of an element that
maintains the properties of that element


HUH?
The smallest unit of an element that
maintains the properties of that element???

The element sodium has certain properties
 11
protons, 11 electrons, etc and that determines
properties like boiling point, etc.
Forming a Compound
Compounds- have properties unlike those
of their elements
ex. Na-shiny, soft, grey metal
Cl- green-yellow gas
NaCl- forms table salt
Chemical formula- tells what elements it contains &
the ratio of the atoms of those elements
Superscript+1
-1
ex. H2O, Na Cl
indicates charge

Subscript-indicates
#atoms
Compounds cont…

Substance made of atoms of 2 or more different
elements that are CHEMICALLY combined.


Means they are bonded by the valence electrons!
Elements are combined in a definite way and this
changes their properties
Na- lethal if ingested
Cl- lethal if ingested
NaCl- table salt
Molecules

Two or more atoms bonded together…
 They
can be two of the same element or two
different elements (compounds)
 All compounds are molecules, but not all molecules
are compounds.
 Ex- O2, NaCl, etc.
Compounds
Molecules made by
atoms of two or more
elements bonded
together -always in a
definite ratio
NaCl (sodium
chloride/salt)

Elements


Made of just one type
of atom
Ex. Sodium is only
made of Na atoms
Na (sodium)
Chemical Bond
Force which holds atoms together.
 2 major types:

Ionic
 Covalent

Why Bond??



Chemically stable- if an atom’s outer energy level is
completely filled with electrons
-most are filled when they contain 8
electrons (OCTET RULE)
(exceptions- He, H, Li, Be)
ex. Noble gases- inert; chemically stable
So, atoms will try to form compounds by doing chemical
reactions and therefore forming bonds.
REMEMBER: ATOMS DON’T LIKE TO BE ALONE!
Why Bond??

Chemical bond- force that holds together the atoms
in a substance
*Losing, gaining, and sharing of valence
electrons are the means that atoms use to become
stable & form chemical bonds.
ex. LiF- Li loses 1 electron
F gains 1 electron
Ionic Bonds (formed in ionic compounds)
Formed between metal & nonmetal atoms
(elements).

IONS are the basic unit (atom with a charge).


CATION = ion that has a + charge (lost e-‘s)
ANION = ion that has a – charge (gained e-‘s)
How are these ions made?





Can you mess with protons?
Would messing with neutrons do
anything to the charge?
What must you mess with???
What charge does an electron
have?
So what would happen to the
atom if they LOSE one? Would
they get more positive or more
negative overall???
How do ions stick together?

Force of attraction between
oppositely charged ions.

(anion & cation)
Ionic bonds are very strong bonds.
 Formed between metal &
nonmetal atoms (elements).
 One atom gives an electron to
another atom (remember it’s the
losing and gaining of electrons)
 Electronegativity difference between
the atoms is 1.7 or greater. (see table
on last page of notes)
 Ex) Na & Cl

Ionic Compounds:
 pack
into a pattern (crystal; lattice)
 have very high melting points.
Ionic Compound Cont…
 Dissolve
in water (H2O), and ions are then free to move
(dissociate).
 Conduct electric current.
Let’s Draw Some:

Do you remember how to draw a bohr model?
Draw one for Sodium and one for Chlorine

What do you think will happen?

Bond Diagrams
Ionic Bond-lose & gain
electrons
 Ex. NaCl

Ionic Bonds


Sodium atom, Na, that lost an electron is now a
sodium ion, Na1+
Chlorine atom, Cl, that gained an electron is now a
chlorine ion, Cl1-
Lets make some Lewis Dot diagrams!!!



Draw a Lewis Dot for
Na & Cl.
Draw an arrow to show
what the electron will
do
Finally draw the ions in
the bond.
Let’s put it all together…
Lewis Dot Diagrams

Types of Bonds
Covalent bond – bond that forms b/w atoms
when they share electrons
-occurs between 2 nonmetals
-types- single (shares 1 pair of e)
double (shares 2 pairs of e)
triple (shares 3 pairs of e)
 Usually forms liquids/gases at room temp.
*REMEMBER HYDROGEN IS A NONMETAL
AND FORMS COVALENT BONDS!!!

Covalent Bonds (formed in molecular/covalent compounds)
Atoms are the basic unit. (atoms bond to form
them)
 Covalent bonds are firm, but molecules not
strongly held together.
 Force between atoms that share electrons.

Let’s draw some!


Remember covalent bonds SHARE electrons, so there
is no drawing arrows.
Ex- F2
Lewis Dot Diagrams…
Covalent bonds
H2-hydrogen gas-sharing of electrons
Steps to help you…



Draw the lewis of each kind of atom in the
compound.
Highlight/circle which electrons will be shared
When you draw your molecule Draw
the center atom in the molecule with all 8 valence
electrons (use two “types” like x’s and o’s to show where
they came from)
 Draw in your other atoms and their valence electrons
 Circle each atoms’ “8 electrons”- they will overlap each
other where they share 
Ex- Cl2
Kinds of Covalent Bonds

Can share different number of electrons:
 Single-
share ONE pair of electrons
 Double- share TWO pair of electrons
 Triple- share THREE pairs of electrons
How do you know which type of bond
will form? Use two rules:



Calculation using electronegativity values on a periodic
table:
Subtract the values of the 2 elements (larger minus
smaller)
If difference is:
0-0.3 = nonpolar covalent bond
>0.3-1.7= polar covalent bond
1.7 & up= ionic bond
Electronegativity Differences
summary…
If difference is 1.7 & up
Electronegativities are so
great that one atom will
steal the electron away
0-0.3 difference
Electronegativities are
the same, so the atoms
will share nicely 
If difference is: >0.3-1.7
Electronegativities are not
different enough to steal the
electron away, but there will be
a “bully” who hugs the
electrons closer
A second way… “rule of thumb”

2) Periodic table/metal, nonmetal rule (Rule of
thumb):
 Metal
and nonmetal = ionic bond
 Nonmetal and nonmetal = covalent
Rule of thumb summary…
A metal with a nonmetal
Two Nonmetals
Covalent/ Molecular Compounds:




Not packed into a pattern.
Have low melting points.
May not dissolve in water (H2O), but some can.
Do not conduct electricity; do not dissociate.