1. Compounds
and
Chemical Bonding

2. Neutral atoms contain an equal number of protons which have a positive charge…
and electrons which have a negative charge. -
electrons
protons +
neutrons
In addition, most atoms contain one or more neutral particles called neutrons.

3. Atoms are naturally balanced
Atoms are naturally balanced. The number of protons is equal to the number of electrons.
However, most atoms are not chemically stable. The outer energy level is not completely filled.
Atoms would rather be stable than balanced, so they share or steal electrons and become compounds.

4. Why do atoms combine?
The positive charge in the proton of one atom is attracted to the negative charge of the electrons in another atom. This attraction is the glue that holds atoms together.
This glue is a chemical bond.The bonded atoms are now a compound.

5. What are compounds? Think about a compound word such as hotdog.
The words hot and dog have defined meanings or properties.
The combined word has a new meaning.

6. + = What are compounds? Compounds are chemically bonded atoms.
The properties of compounds are different than the properties of uncombined atoms.
For example, sodium (Na) is a soft, shiny metal that reacts violently with water.
Chlorine (Cl) is a toxic, yellowish gas.
When combined, NaCl is table salt. + =

7. What properties are used to position elements on the periodic table?1 2
2 2A
133A
144A
155A
166A
177A 1 3 4 5 6 7 8 9 10 2
3 3B
4 4B
5 5B
6 6B
7 7B B
111B
122B 3 4 5 6 7
# of protons = atomic number
# of energy levels = period
# of valence electrons = group or family

8. This is a Bohr model of a calcium atom.
How many electrons are present in the last energy level? + -
Only the outer shell, or valence electrons are involved in bonding. In general, atoms form compounds in order to have 8 outer shell electrons. With 8 outer shell electrons, atoms are chemically stable.

9. Chemical Formulas

10. Consider the formula for water:
Chemical Formulas
describe compounds
list which atoms are present in the compound
express the ratio of each atom present
Consider the formula for water:
H2O
The small 2 is a subscript. It indicates that for each molecule of water, 2 atoms of hydrogen are present for each atom of oxygen.

11. Consider the formula for aspirin:
Consider the formula for potassium nitrate:
KNO3
How many atoms of nitrogen are present?
How many atoms of oxygen are present?
How many atoms of potassium are present?
Consider the formula for aspirin:
6C9H8O4
How many atoms of oxygen are present?
How many atoms of hydrogen are present?
The six is a coefficient. It tells us how many molecules of the whole compound are present. Multiply the coefficient and subscript to determine the number of atoms of each element present in the formula.
How many atoms of carbon are present?

12. Bibliography
Bonding. (1999). Chemzone Ithaca City School District. Available. [Online]
Hsu, Tom. (2002). Integrated Physics and Chemistry. Peabody, MA: Cambridge Physics Outlet.
American Chemical Society. (2002). Chemistry in the Community Fourth Edition. New York: W.H. Freeman and Company.
Ions. ( ). Chem4Kids Andrew Rader Studios. Available. [Online]