Structure of Matter……….
 Elements - combine to form …..
 Compounds - combine to form….
 Molecules
Formulas and Symbols
 Elements are represented by chemical
symbols found on the periodic table.
 Examples: H, N, S, O, P, Au, Hg, Na
 Compounds are represented by
chemical formulas
 Examples: H2, NO2, NH3, O2, NaCl, C6H6O6
Compounds and molecules
 – the attractive force
that holds atoms or
ions together
Compound
Na
+
Cl
--->
NaCl
Water is a compound….
Compounds
 What are compounds?

- Chemical bonds distinguish
compounds from mixtures
 A compound always has the same chemical formula
 Chemical structure shows the bonding within a
compound
Compounds
 Made of 2 or more
elements chemically
joined
 Pure substances
 Made up of
molecules
 All molecules of a
compound are
identical
water molecules
Structure
– the arrangement of bonded atoms or ions
within a substance
Models of Compounds
 Ball-and-stick model
helps you “see” a
compound’s
structure by showing
you how the atoms
or ions are arranged
in the compound
Models of Compounds
 Structural Model –
also shows the
structures of
compounds. Each
connecting line
represents a bond
between elements.
Oxygen has six
valence electrons
available for
bonding. Each
hydrogen atom has
only one.
Models of Compounds
 Space-filling models
– show the space
occupied by atoms
(the problem with this
model is that it is
harder to “see” bond
lengths and angles
The space-filling model
of water shows that the
two hydrogen atoms
take up much less space
than the one oxygen atom.
Lewis Dot Structure
 Shows bonds
represented by
lines of shared
pairs of electrons
and dots to
represent the “leftover” valence
electrons.
Hydrogen Bonding
Dotted lines indicate intermolecular attractions that occur between
water molecules, which is often referred to as “hydrogen bonding”.
Water is a liquid at room temperature because of these attractions.
Bonding….
 Elements “want” to bond with another
element that will help it follow the octet rule
 when elements have either a full or empty
valence energy level – full usually with 8*
*except for Hydrogen & Helium 
Lewis Dot Structure for
Molecules
 Bonds are represented by lines
 Each line represents two shared electrons
 Molecules follow the OCTECT rule
Step by step…..
1. Count the total number of valence
electrons available.
1.
2.
3.
4.
For water – H2O
Hydrogen in Group IA has 1
Oxygen in Group VIA has 6
H2O = 2 for hydrogen and 6 for oxygen = 8
2. Draw a “skeleton structure” for the
molecule, joining atoms by single bonds.
2. A molecule H2O
would be
H -- O -- H
Step by step…..
3. From the total number of valence
electrons, subtract two for each single
bond in the skeleton structure to
determine how many valence electrons
are left to distribute.
3. H2O has a total of 8 valence electrons.
Subtract 2 for each single bond (each line)
(2 x 2 = 4) : 8 - 4 = 4 remaining valence
electrons
Step by step…..
4. Distribute the remaining valence electrons
as unshared PAIRS around the atoms in
the molecule. (No single electrons)
..
H -- O -- H
..
Step by step…..
5. If this point is reached and there are an
odd number of valence electrons to give
atoms, a multiple bond is most likely
necessary as well as shared pairs.
5. Example: HCN has a total of 10 valence
electrons – 1 for H; 4 for C and 5 for N
6. Each line represents two – a double bond
between carbon and nitrogen would still leave
1 electron for Carbon and 3 for Nitrogen – use
another bond for 1 C and 1 N then draw 2 at N
H-C=N:
Other looks for structures
You try……………..
 Draw Lewis Dot Diagrams for these:
1.
2.
3.
4.
5.
HBr
PBr3
N2H2
C2H4
CH3OH
More………
1. BSF
2. HCl (Hydrogen and Chlorine) not
Hydrogen Carbon and Iodine
3. C2H5OH
4. N2F4
5. SF6