1. Chp.3: Chemical Bonding and Chemical Reactions Test
Study Guide

2. Molecules
A substance made of 2 or more elements. Example: O2=oxygen gas

3. Compound
A compound is made of 2 or more different kinds of elements. (2 Hydrogens and one Oxygen, H2O=water). All compounds are molecules.

4. Covalent Bond A chemical bond between two or more non- metals.
Ex: CO2=Carbon and Oxygen=Carbon Dioxide

5. Ionic Bond
A chemical bond between at least one metal and one or more non-metals.
Ex: CaO=Calcium and Oxygen=Calcium Oxide

6. Metallic Bond A chemical bond between two or more metals.
Ex: Al2=Aluminum

7. Chemical Formula
Uses element symbols and numbers to represent the elements in a molecule/compound.
Ex. Salt=NaCl (1 sodium and 1 chlorine atom)

8. Subscripts
A subscript is a little number on the bottom right hand side of an element that represents the number of elements in a chemical formula.
Ex. H2O4 =2 Hydrogens and 4 Oxygens = 6 atoms
Ex. C6H12O6 = =24 atoms

9. Coefficients
A coefficient is the number of molecules in a reaction. It is represented by a large number is front of a molecule.
Ex. 3H2O = 3 water molecules, or
H2O, H2O, H2O

10. Counting Atoms
If there are coefficients and subscripts in a molecule, you multiply the coefficients times the subscripts to find out the number of atoms.
Ex. 4H2O4
4x2=8 Hydrogens, 4x4=16 Oxygens, =24 atoms

11. How to write a chemical formula for a given compound
Ex: If given the compound, calcium chloride, what is the chemical formula? CaCl2
You’ll need to look at a Periodic Table to determine the number of atoms a compound needs.
Ex.CaCl2 = Calcium has two valence electrons in its outer shell and Chlorine needs one electron, so Calcium will give one electron to one Chlorine atom and another electron to another Chlorine atom.

12. (POH + H2O4 ---> P2O4 + H2O)
Chemical Equations
A Reactant is the molecule or molecules on the left side of a chemical equation.
The Product is the molecule or molecules on the right side of a chemical equation.
(POH + H2O4 ---> P2O4 + H2O)
Reactants
Products

13. Law of Conservation of Mass
Matter/mass cannot be created or destroyed, but preserved or transferred.
Ex.  H2O2 = 2HO
This is why chemical equations must be balanced.

14. Balancing Chemical Equations
There must be the same number of different atoms on the reactant side as the product side.
To balance you can only add coefficients NOT subscripts.
First list the number of atoms by counting them to see how many you are starting with. Remember if there is no subscripts next to an atom (element symbol), that means there’s just one of them.
Plug in coefficients until it works.
Sometimes you have to play with it to make it balanced.

15. Balancing Chemical Equations Cont.
Ex. (This is not balanced)
POH + H2O4 ---> P2O4 + H2O
P=1
O=5
H=3
P=2
O=5
H=2

16. Balancing Chemical Equations cont.
Ex. (This is balanced)
2POH + H2O4 ---> P2O4 + 2H2O
P=2
O=6
H=4
P=2
O=6
H=4

17. Physical and Chemical Changes
In a physical change the substances are not altered but can change state of matter, but they keep their original properties.
In a chemical change the substances are altered chemically to produce a new substance with different properties after the change.

18. Physical and Chemical Changes cont.
Ex. of physical changes
-salt dissolving in water, ice melting, chopping wood
Ex. of chemical changes
-an iron rusting, baking cookies, wood burning

19. Precipitate
A solid is formed as evidence of a chemical change.

20. Types of Chemical Reactions
Synthesis: 2 or more elements or compounds combine to make a more complex substance.
=A =B
Ex. A+B AB; +
P+O PO2
Decomposition: Compounds break down into simpler substances. (opposite of synthesis)
Ex. AB A+B;
PO P+O2

21. Types of Chemical Reactions cont.
Single Replacement: Occurs when one element replaces another one in compound.
=A =B =C =D
Ex. AB+C AC+B;
HgO+Cl HgCl+O2
Double Replacement: Occurs when different atoms in two different compounds trade places
Ex. AB+CD AD+CB;
NaCl+AgNO NaNO3+AgCl

22. Types of Chemical Reactions cont.
Combustion: A substance combines with oxygen and releases energy.
a substance + O substance(s)
Ex. C3H8 +5O2 3CO2+4H2O