1. Chemical Compounds
Chapter 20

2. A. Elements that combine chemically no longer have the same properties
B. Chemical Formulas are composed of symbols and subscripts that indicate the number of atoms of each element

3. C. Atoms form compounds when the compound is more stable than separate atoms
1. Noble gases have complete outer shells, so they are more chemically stable 2. Elements that do not have complete outer shells are more reactive, but are more stable as compounds than elements 3. Atoms can lose, gain, or share electrons 4. A chemical bond is the force that holds atoms together

4. 20.2 A. An ion is a charged particle
1. When an atom loses an electron it becomes positively charged (has more protons than electrons) 2. When an atom gains an electron it becomes negatively charged (has less protons than electrons)
Some examples are sodium chloride, commonly known as table salt; sodium fluoride, an anticavity ingredient in some toothpastes; and potassium iodide, an ingredient in iodized salt.

5. B. Ionic Compounds: Held together by an ionic bond when atoms gain/lose electrons
1. The result is a neutral compounds 2. Net sum of charges is zero

6. C. Molecules are formed as a result of sharing electrons
1. A Covalent Bond is the force of attraction between atoms sharing electrons, a molecule is formed 2. Can form double or triple bonds 3. Electrons are held more closely to the atoms with the larger nucleus

7. A Polar molecule has one negative and one positive end
5. A Nonpolar molecule both ends are either positive or negative
Polar or Nonpolar??

8. 20.3 Writing and Naming Chemical Formulas
Use Symbols to represent elements in writing formulas
Binary Compounds are composed of two elements
Oxidation Number- How many electrons an atom has gained, lost, or shared until it becomes stable
Use Oxidation Numbers to write formulas
a. Compounds are always neutral
b. A formula must be balanced, by having the same amount
number of positive and negative ions
In writing a formula use the name of the first element, the root name of the second element, and the suffix - ide to write the name of the compound.
*Oxidation Numbers used only in IONIC Bonds*

9. Polyatomic Ion- Positively or Negatively charged atoms
1. Contains three or more elements
2. Write the name of the positive ion first, then the
name of the negative ion second
To write formulas use the oxidation numbers, their
least common multiple,
and put parentheses
around the ion before
adding a subscript to
represent the number of
atoms

10. Hydrate compounds have water chemically attached to the ions
Name the binary (2 elements) covalent (shared) compound by using prefixes to indicate how many atoms of each element are in the compound
Examples:
Carbon Dioxide: CO2
Carbon Monoxide: CO
*Prefixes used only in COVALENT Bonds *

11. Practice Naming COVALENT Binary Compounds:
Silicon Dioxide
Iodine Trichloride
Dihydrogen Oxide
SiO2
ICl3
H2O
N2O5
CaCr2
Na4Cl
DiNitrogen PentaOxygen
Calcium DiChromide
Tetrasodium Chlroide

12. Practice Naming IONIC Binary Compounds
Sodium bromide
2. Silicon oxide
3.Lithium carbonite
Oxidation Number of
Na= +1
Br=  NaBr
Oxidation Number of
Si= -4
O=  Si2O4  SiO2
Oxidation Number of
Li = +1
C=  Li4C