CHEMICAL BONDING
p. 144-156
REMEMBER….
THERE ARE TWO KINDS OF PURE
SUBSTANCES
Elements
Compounds
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, reactivity, etc.
Compounds cont…


Substance made of atoms of 2 or more different
elements that are CHEMICALLY combined.
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- this would be a compound
 All compounds are molecules, but not all molecules
are compounds.
 Ex- O2, NaCl, etc.
Compounds
Molecules made by
two or more elements
bonded together always in a definite
ratio
NaCl (sodium
chloride/salt)

Elements

Molecules made of
just one element
Na (sodium)
Let’s start the new notes…
Compound/Molecule



Chemical combination of 2 or more elements.
Properties of the compound are unlike those of the
elements that make it.
Represented by a formula that gives the ratio of
atoms of the elements.
 Ex-
The formula NaCl tells you that salt is a compound
made of one Na and one Cl.
 The
ratio is then 1:1
Chemical Bond
Force which holds atoms together.
 3 Types:

Metallic
 Ionic
 Covalent

Polar
 Nonpolar

Metallic Bonds




Formed between 2 or more metal atoms (elements).
Valence electrons overlap.
The electrons are free to move about all the atoms;
therefore, they are good conductors of electricity.
Ex) Mg, Cu, Fe, etc. form these types of bonds
Ionic Bonds (formed in ionic compounds)

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).
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.
Covalent Bonds (formed in molecular/covalent compounds)
Atoms are the basic unit.
 Covalent bonds are firm, but molecules not
strongly held together.
 Force between atoms that share electrons.

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


Can be polar covalent or nonpolar covalent
bonds.
Nonpolar Covalent bonds:





Electrons are shared equally in the bond.
Does not have (+) and (-) end to the bond.
Formed between 2 or more of the same nonmetal.
Electronegativity difference between the atoms (elements) is 0.
(see table on last page of notes)
Ex) Cl & Cl
Polar Covalent bonds:





Electrons are NOT shared equally in the bond.
Has a (+) and (-) end to the bond.
Formed between 2 different nonmetals.
Electronegativity difference between the atoms (elements) is 0.11.6 (see table on last page of notes)
Ex) H & O
C&O
Polar vs Nonpolar Covalent Bonding
How do you know which type of bond
will form? Use two rules:



Calculation using electronegativity values on a periodic
table: (Note: if they are both/all metals, automatically,
it is a metallic bond!)
Subtract the values of the 2 elements (larger minus
smaller)
If difference is:
0= nonpolar covalent bond
0.1-1.6= polar covalent bond
1.7 & up= ionic bond
Electronegativity Differences
summary…
If differenc is 1.7 & up
Electronegativities are so
great that one atom will
steal the eletron away
0 difference
Electronegativities are the
same, so the atoms will
share nicely 
If difference is: 0.1-1.6
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 Metal
= metallic bond
 Metal and nonmetal = ionic bond
 Nonmetal and nonmetal = covalent
 All
same nonmetal = nonpolar covalent bond
 Different nonmetals = polar covalent bond
Rule of thumb summary…
A metal with a nonmetal
Two Metals
Both the same metal
Two different 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.