Chemistry for Biology Page
All you ever wanted to know about chemistry: Chem4kids
4. Atomic Number = the number of protons (and also
electrons)
5. Atomic Mass = the number of protons + neutrons
6. The number of neutrons = Atomic Mass - Atomic Number
7. EXAMPLE: Chlorine has atomic number 17 and
atomic
mass 35;
therefore, it has 17 protons, 17 electrons, and 18 neutrons.
B. Definitions
1. energy level-- a certain distance from the nucleus
of
an atom
The first energy level can only hold 2 electrons;
the second energy level can only hold 8 electrons;
the third energy level holds 8 electrons, then puts
two electrons in the fourth energy level;
then .... (I'll stop here)
2. orbital-- the path that an electron follows within
its
energy level
3. atomic structure
4. ion--
any atom with a charge; H+ is the
hydrogen
ion; OH- is the hydroxide ion
5. inert-- an atom whose last energy level is naturally filled;
consequently it is nonreactive.
6. isotope-- atoms of the same element with different numbers
of neutrons.
7. molecule-- (very simplified definition)-- 2 or more atoms
which
are chemically combined
8. compound-- 2 or more different atoms which are chemically
combined.
9. isomers-- molecules with the same molecular formulas but
different structural formulas
C. Periodic Table of the
Elements
1. Groups = the columns of the periodic chart
= the number of electrons in the last energy level
2. Periods = the rows of the periodic chart
= the number of energy levels
D. Chemical Bonds
1. Ionic
bonds-- involve the total loss and gain of electrons;
then
the positive atoms are attracted to the negative atoms.
2. Covalent
bonds-- involve the sharing of electrons;
D. Formulas
1. Molecular formulas, such as 3H2O, indicate
the
a. kind of atoms in the molecule
b. number of each kind of atom in the molecule
c. number of molecules
2. Structural formulas indicate
a. kind of atoms in the molecule
b. number of each kind of atom in the molecule
c. position of each atom in the molecule
E. Chemical Reactions
1. During a chemical reaction, atoms are rearranged.
2. Two types of reactions:
a. anabolic- "building up" reactions
(synthesis)
usually
requires energy (endergonic)
b. catabolic- "breaking down" reactions
usually
releases energy (exergonic)
these reactions may occur spontaneously
3. Parts of a reaction:
a. reactants- molecules the reactions starts with
the arrow always points away from reactants
b. products- molecules which result from the reaction
the arrow always points toward the products
c. EXAMPLE: H2 + O2 --> H20
In the above example H2 and O2 are the
reactants,
and H2O is the product.
4. Balancing Equations
a. A balanced chemical equation shows the quantity of the reactants
and products.
b. A balanced chemical equation has the same
number atoms of each element on both sides of the equation.
This is to adhere to the law of conservation of mass. In other
words, atoms cannot disappear during a
reaction, neither can they just appear from nowhere.
c. EXAMPLE: the equation above is not balanced: H2
+ O2 --> H2O There are
two hydrogen atoms for
the reactants and two hydrogen atoms for the products, so the hydrogen
atoms are balanced. However,
there are two oxygen atoms in the reactants and only one oxygen atom
shown in the product- the oxygens
are not balanced. To balance the equation:
1. be
sure that you only change the coefficient in front of each listed
molecule
2.
start with the element that is not balanced, and change the coefficient
so that it is balanced.
3.
count the atoms of each element and balance any remaining elements that
are not balanced.
4. repeat step #3 until all elements
are balanced.
5. In the example above, start
balancing the oxygens by putting a 2 in front of H20:
H2 + O2
--> 2H2O
6. Now there are two oxygen atoms on each side of
the equation. But, now there are two hydrogen
atoms in the
reactants, but 4 hydrogen atoms in the products. We need to
balance the hydrogen
atoms by getting two
more hydrogen atoms in the reactants. We can do this by changing
the
coefficient in front
of H2 to a 2:
2H2 + O2
--> 2H2O
Now there are 4 H atoms on
each side of the equation, and there are 2 atoms of oxygen on each
side of the
equation; so the equation is balanced.
7. Try
these problems: practice
problems
8. Try these links
for more information and practice in balancing equations:
i. Classic
chembalancer -- computer practice in balancing equations
ii. About.com:
chemistry
F. Mixtures and Solutions
1.
Mixtures- when two substances are physically combined, such as
sand and paperclips mixed, sugar and salt mixed, or
water and sand mixed together.
2. Solution-
when one substance is dissolved in another substance.
a. Solute-
the substance that IS dissolved.
b. Solvent-
the substance that DOES the dissolving.
c. Example: sugar and water mixed; the sugar is dissolved
in the water, so
sugar is the solute and water
is the solvent.
d. Water is the universal solvent, because it can
dissolve so many substances.
G. Acids and Bases
1. An acid is
a solution with more H+ than OH-
2. A base is
a solution with more OH- than H+
3. Another
name for base is alkaline
H. pH Scale
1. The pH scale
is an indication of the amount of H+ or OH- in a
solution.
2. The pH scale
ranges from pH 0 to pH 14.
3. A pH from 0
to 7 (not including 7) indicates more H+ than OH-,
so
any solution in this range would be an acid.
4. A pH from 7 to 14 (not including
7) indicates more OH- than H+, so
any solution in this range would be a base.
5. A pH 7 indicates
equal amounts of H+ and OH-, so a solution of pH
7 would be neutral.
6. The farther away
from pH 7 the pH of a substance is, the stronger it is. For
example,
pH 3 is a stronger acid than pH 6; pH 11 is a
stronger base than pH 9. Likewise,
pH 6 would be a weak acid, and pH 8 would be a weak base.
II. Links
