Chemical Reactions
Chapter 14 Section 1
Forming New Substances
Chemical reaction – process by which one
or more substances undergo change to
produce one or more different substances.
The new substances have different
chemical and physical properties from
the original substances.
An example is when chlorophyll in leaves
breaks down into simpler substances. The
green that covered the colors is gone and the
red, orange, and yellow colors show through.
What happens during a chemical reaction?
- chemical bonds break
- atoms rearrange
- new bonds form
Some clues to a chemical reaction:
Gas formation (bubbling, fizzing)
Solid formation (precipitate forms)
Color change
Energy change
Chemical formula – a shorthand notation
for a compound or a diatomic element
using chemical symbols and numbers.
The chemical formula shows how many of
each kind of atom is present in a molecule.
The chemical formula for water H2O shows
that the water molecule has
2 atoms of hydrogen and 1 atom of oxygen.
The formula for carbon dioxide CO2 has
1 atom of carbon and 2 atoms of oxygen.
The formula for glucose (sugar made by
plants during photosynthesis) is C6H12O6.
Every molecule of glucose has
6 atoms of carbon
_____
12 atoms of hydrogen
_____
6 atoms of oxygen
_____
Prefixes Used in Chemical Names
mono
di
tri
tetra
1
2
3
4
penta 5
hexa 6
hepta 7
octa 8
nona 9
deca 10
The formulas of covalent compounds
(between nonmetals) are written using prefixes.
carbon dioxide – CO2
carbon monoxide – CO
carbon tetrahydride – CH4
Formulas for ionic compounds (between a
metal & nonmetal) must be written to make
sure the overall charge is zero or neutral.
NaCl
sodium has a 1+ charge & chlorine has a 1- charge
The overall charge is (1+) + (1-) = 0
MgCl2
magnesium has 2+ & chlorine has 1- charge
2 chlorine atoms are needed for 1 magnesium atom
The overall charge is (2+) + (1-) + (1-) = 0
Write the formula for sodium nitride.
1+ charge.
Sodium has a ____
3- charge.
Nitrogen has a ____
The formula is Na__N
__.
3
Write the formula for potassium oxide.
1+ charge
Potassium has a ____
2- charge
Oxygen has a ____
The formula is K__O
__.
2
Ionic or Covalent? (check the elements)
Write the formula.
1. sulfur trioxide
_________
covalent
SO3
______
2. calcium fluoride
ionic
_________
CaF2
______
3. phosphorus pentachloride covalent
_______
PCl5
______
covalent
_________
ionic
_________
N 2O 3
______
4. dinitrogen trioxide
5. lithium oxide
Li2O
______