1. Compounds and Molecules
Section 4.1

2. What are compounds? Atoms which have combined with other atoms
They are pure substances
They can be written using a chemical formula
Like H2O, CH4, C12H22O11, etc.
They have their own physical and chemical properties, which may be different than the atoms that make them up
A compound always has the same chemical formula

3. What holds compounds together?
Chemical bond: The attractive force that holds atoms or ions together
There are numerous types of bonds:

4. How strong are chemical bonds?
Chemical structure: The arrangement of bonded atoms or ions within a substance
Bond length: average distance between nuclei (nucleuses) of two bonded atoms
Bond angle: the angle formed by two bonds to the same atom

5. Models of Compounds
Models help you “see” the structure of a compound by showing how atoms are arranged.
Structural Formula model
Ball and Stick model
Space filling model

6. What are the major types of chemical structures?
Network structures
Bonded ions
Molecules

7. Network Structures Examples: All are strong solids
SiO2 (silicon dioxide, quartz, sand)
MgF2 (magnesium fluoride)
NaCl (table salt)
All are strong solids
Lots of energy is needed to break the bonds, so all have high melting points
SiO2: 1700˚C
MgF2: 1261˚C
NaCl: 801˚C

8. Bonded Ions Some networks are made of bonded ions Examples:
NaCl (table salt)
LiF (lithium fluoride)
KI (potassium iodide)
Oppositely charged ions form bonds that pack themselves close together

9. Molecules
Examples:
C12H22O11 (table sugar)
H2O (water)
H2S (dihydrogen sulfide)
Much weaker attractions for other molecules than in bonded ions or network solids
Have much lower melting temperatures because of that
sugar : 186˚C
water: ˚C
hydrogen sulfide : -85˚C

10. Summary
Chemical Compounds
Bonded
Ions
Network
Structures
Molecules