1. Topic 6
Molecular Compounds

2. There are over 112 elements so far!
When elements join together, they form compounds.
Elements are held together by chemical bonds.
These bonds are formed when elements gain, lose, or share electrons.
A molecular compound is formed when atoms share electrons.

3. Properties of Molecular Compounds
Formed from only non-metallic elements
(REMEMBER: what side of the periodic table are non-metals located?)
Do NOT form ions in solution
Usually do NOT conduct electricity
Solid, liquid or gas at room temperature

4. What’s in a Chemical Formula?
Symbol for the element oxygen
Symbol for
chemical element hydrogen
H2O(l)
This means the state of the compound:
(l)- liquid
(g)- gas
(s)- solid
(aq)- aqueous
The small number here means 2 atoms of hydrogen (subscripted number)
No small number means 1 atom of oxygen

5. A chemical formula uses symbols and numerals to represent the composition of a pure substance. Each symbol in a chemical formula represents an atom of an element.
If there is more than one atom of an element, a small number written below the line ( a subscript) follows the elements symbol
The subscript shows the number of atoms.
The Law of Definite Composition tells us that every pure substance has a fixed and definite composition. Ex: (H2O) ALWAYS contains two atoms of hydrogen for each atom of oxygen.

6. # of atoms of each element per molecule Total # of atoms per molecule
Formula
Elements
# of atoms of each element per molecule
Total # of atoms per molecule
# of molecules
Total # of atoms N2
CH4
5Ca(OH)2

7. MOLECULAR COMPOUNDS
A molecule is the smallest independent unit of a pure substance and is generally a cluster of atoms joined together.
Diatomic molecules are molecules made of two atoms of the same element.
Examples:
oxygen O2
nitrogen N2
hydrogen H2

8. The Rule of “-gen”
These are all of the DIATOMIC elements in the periodic table
Includes:
All of group 17 (halogens)
oxygen
nitrogen
hydrogen

9. The BONDING between ATOMS is strong, but the attraction between MOLECULES is weak.
When you melt or vaporize a molecular compound, you must supply enough energy to overcome the attraction between the molecules.

10. This is ELECTROLYSIS! WATER MOLECULES Oxygen atom Hydrogen atom
Hydrogen molecules
Oxygen molecules

11. IUPAC makes recommendations on how compounds should be named.
Not only do elements have universal symbols that are recognized world-wide, but compounds are also named according to global guidelines.
The international Union of Pure and Applied Chemistry (IUPAC) is an organization of scientists responsible for setting standards in chemistry.
IUPAC makes recommendations on how compounds should be named.
There are rules to naming compounds.
Ex:
A compound made up of two elements is called a binary compound. The names of molecular binary compounds follow these rules.

12. Language
Name of element
Symbol
English
hydrogen H
French
hydrogene
German
wasserstoff
Italian
idrogeno
Portuguese
hidrogenio
Spanish
hidrogeno

13. Naming molecular compounds!
Hmm… what is this? CO2 (Use your periodic table)
Write the entire name of the 1st element
carbon
Change the ending on the name of the 2nd element to “-ide”
oxygen  oxide
Use a prefix to indicate the number of each type of atom in the formula
carbon dioxide

14. PREFIXES REMEMBER: You only use MONO- for the second element! 1- mono
2- di
3- tri
4- tetra
5- penta
6- hexa
7- hepta
8- octa
9- nona
10- deca
REMEMBER:
You only use MONO- for the second element!

15. Let’s do a couple examples:SO
CCl4
S3O6
P4O10

16. Name these:
H2O2
HCl7 CO
SO2
H2O

17. If you are changing from the written name to the symbol:
Write the symbols for the elements in the same order as they appear in the name
Use subscripts to indicate the numbers of each type of atom

18. Let’s do these:
carbon tetrachloride
Silicon dioxide
Sulfur dioxide

19. Some molecular compounds are known by common names as well as by chemical names
FORMULA
DESCRIPTION
CO(g)
Carbon tetrachloride
Silicon dioxide
SO2(g)

20. To do:
Naming Molecular Compounds
Molecular Model Kits