1. Chapter 5.2
Molecular Substances

2. Most solid compounds at room temperature are ionic.
Most liquid and gas compounds at room temperature are covalent.
There are exceptions to these rules.
Exceptions: solid covalent cpds.
Sugar
Moth balls
Sand
Butter

3. Covalent compounds/molecules are much more variable than ionic cpds.
Differences due to fact that covalent bonds are weaker than ionic bonds.
Covalent compounds react very differently due to different bond strengths.
Ex: diamonds- hard, carbons tightly bound to each other
crayons and wax- soft and have low melting point due to weak bonds

4. Separation of Substances
Distillation:
Method of separating substances in a mixture by
evaporation of the liquid and condensation of its vapor

5. Molecular Elements I. Molecular Element:
molecule with two or more of the same element
- Diatomic elements: 2 of same elements in a cpd.
7 found naturally in diatomic state
H2 gas at RT H : H
N2 “ “ N ::: N
O2 “ “ O :: O
F “ “ F : F
Cl2 “ “ Cl : Cl
I2 solid at RT I : I
Br2 liquid at RT Br : Br
WHY ARE THESE NOT FOUND AS MONOATOMIC ELEMENTS?

6. Allotropes:
forms of elements that differ in the way the atoms are bonded
- have different structures of the same element
- properties of allotropes differ from the single element and from other allotropes

7. Allotropes A. Oxygen Allotropes O2 (diatomic) O=O Ozone (O3)
- formed by:
O2 + uv light or lightning
O2 + pollution (smog)
layer in upper atmosphere, filters out harmful UV light

8. Allotropes B. Carbon Allotropes
- most versatile element in forming different structures of covalent bonds (4 valence electrons)
can make more covalent bond formations than any other element
Eight allotropes of carbon:
a) Diamond b) Graphite
c) Lonsdaleite d) Buckyball C60
e) C540, f) C70 g) Amorphous carbon
h) Single-walled carbon nanotube

9. Phosphorous Allotropes
- white: ignites in air,
flares
- black: semiconductors
- red: match sticks
* differences result from temperature and pressure during formation

10. Formulas and Names of Molecular Compounds
Types Molecular Compounds
Inorganic: no carbon
ex: HCl, NO2, H2O, SO4
2. Organic: contain carbon
ex: CO2, C2H6O3, CH4, CCl4

11. Naming Inorganic Compounds
Rules
1. Write name of first non metal
2. Write name of second non metal and change ending to “ide”
- first element should be further left on periodic table (except H)
- if both in same group, first element should be closer to bottom of periodic table
3. Add a prefix to each element to tell how many atoms of each element are present
- if first element has only 1 atom, not necessary to write “mono”
4. If using prefix “mono” and o-o or o-a are next to each other, drop the first “o” or “a”
ex: monooxide  monoxide
pentaoxide  pentoxide

12. Write the names of the following molecules:
BF3
PBr5
C5H9
IF7
N2O6
SiO2
H2S
N8O4
CS2
P4O10

13. Write the formulas for the following molecules:
Carbon tetrachloride
Sulfur trioxide
Dinitrogen pentoxide
Carbon monoxide
Nitrogen monoflouride
Phosphorous pentachloride
Disulfur hexaselenide
Tricarbon heptabromide
Hydrogen monochloride
Octasulfur diastatide

14. Formal vs Common Names Formal Name
tells chemical composition of compound
ex: CCl4 carbon tetrachloride
NaCl sodium chloride
H2O dinitrogen monoxide
Common Name
“nickname”, easier to say, does not tell composition
ex: NaCl salt
H2O water
HCl hydrochloric acid
H2SO4 sulfuric acid
HNO3 nitric acid
NH3 ammonia

15. Organic Compounds Contains carbon
Names based on hydrocarbon bonds (H-C)
Hydrocarbon: organic compound that contains only hydrogen and carbon atoms
Found in fossil fuels (gas, petroleum)
Form long chains as compounds
Ex: CH4 methane
C3H8 propane
C4H10 butane
C8H18 octane

16. Study for the test !