CP Biology
Name
UNIT 2A: Basic Chemistry
Chapter 2: The Chemistry of Life
2.1 – The Nature of Matter
_KEY__
____________
The Structure of an Atom
Living things share a major fundamental similarity with
nonliving matter. All matter is made up of atoms.
*Atom: the basic unit of all matter
Atoms are incredibly small in size, yet they themselves are
made of even smaller subatomic particles called
protons, neutrons and electrons.
Protons and Neutrons have about the same mass but not the
same electrical charge.
Protons and neutrons are bound by strong forces which
form the nucleus or center of the atom.
The electron is a charged particle with 1/1840th the mass of
a proton. The energy of their constant motion keeps them
outside the nucleus, despite their attraction to the nucleus.
Because atoms have equal numbers of electrons and
protons, their positive and negative charges balance out
and atoms themselves are electrically neutral.
Complete the Chart Below:
Subatomic
Particle
proton
Electrical
Charge
+1
positive
neutron
0
neutral
electron
-1
negative
Location
within atom
nucleus
nucleus
Moving rapidly in energy
levels (electron cloud)
surrounding the nucleus
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A chemical Element is a pure substance that consists
entirely of one type of atom.
Element Name and Symbol
1) ___C____ is the symbol for Carbon
2) Na is the symbol for ___Sodium_______
More than 100 elements are known, but only about two
dozen are commonly found in living organisms.
Mass Number
________________________________________________ You may see a decimal number for the mass on the periodic
The Periodic Table of Elements
table because this is the average mass for the atoms of this
(see picture of periodic table on the last page)
element. Some atoms differ slightly in mass due to different
number of neutrons. These are called isotopes and will be
The Periodic Table of Elements is a reference tool we use to
studied next year in Chemistry. For Biology class we will round
gain information about different elements. Elements are
this number to the nearest whole number.
arranged in order by their atomic number. By using the
periodic table we can determine 3 things:
1) Element Name and Symbol – a symbol is usually 1
or 2 letter abbreviation for the element’s name.
3) The mass of Oxygen is ___16 amu________
4) The mass of Chlorine is ____35 amu________
Atomic Number
2) Mass Number – this is the sum of the protons and
the neutrons in the nucleus. The electrons don’t count
in the mass since their mass is next to nothing.
3) Atomic Number – the number of protons in the
nucleus of an element.
Important Biological Elements
The five most abundant elements in living things are:
1. Hydrogen – 10%
2. Oxygen – 65%
3. Nitrogen – 4%
4. Carbon – 19%
5. Phosphorus – 1%
5) The atomic number of Hydrogen is ___1_______
6) The atomic number of Sodium is ____11______
Protons and Electrons
7) Carbon has __6___ protons and __6___ electrons.
8) Lithium has __3___ protons and __3___ electrons.
Label the
Important
Biological
Elements 
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Chemical Compounds
In nature, it is common to find elements combined with
other elements in compounds.
*Compounds: a substance formed by the chemical
combination of two or more elements in definite
proportions.
*Coefficient: tells how many molecules of that substance
(the large number BEFORE the formula)
*Subscript: goes with the element symbol preceding the
number; tells how many atoms of that element within one
molecule of the substance (small number WITHIN the
formula.
The physical and chemical properties of a compound are
usually very different from those of the original elements
from which it is formed.
We show the composition of chemical compounds by a
kind of shorthand known as a chemical formula.
Example 1: What is the chemical formula for water which
contains two hydrogen atoms and one oxygen atom?
__H2O___
Example 2: 6CO2
What is the coefficient? __6_____
What is carbon’s subscript? __1______
What is oxygen’s subscript? ___2_____
How many molecules of this compound are
represented by this formula? __6_______
e) How many atoms TOTAL are present in this
molecule? ___18______
a)
b)
c)
d)
Use the following information on chemical names and
chemical formulas to fill in the chart below:
Example : NaCl (Table Salt)
NaCl is formed from one atom of sodium a highly reactive,
soft, silver-colored metal AND one atom of chlorine a
poisonous yellow-green gas.
Chemical formulas tell us:
a) They types of elements (atoms) that are present in the
compound.
b) The number of atoms of each element present in the
compound.
Carbon – 1
Hydrogen - 4
Hydrogen – 2
Oxygen - 1
Carbon - 1
Oxygen - 2
Nitrogen - 1
Hydrogen - 3
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Chemical Bonds
The atoms in compounds are held together by various types
of chemical bonds.
Bond formation involves the electrons that surround each
atomic nucleus.
*Valence Electrons: the electrons in an atom that are
available to form bonds (these are unpaired electrons
which are found in the outermost energy level of the
atom’s electron cloud).
*Octet Rule: the outermost energy level of most atoms will
be complete when containing 8 electrons. Atoms will tend
to gain, lose, or share electrons to achieve stability by
having a full outer energy level (stable octet).
~ Do you think Carbon, Oxygen, Nitrogen and Hydrogen
are reactive (unstable) atoms? Explain.
Yes, in each case, there is a vacancy in the outer energy level. H
has one vacancy in the 1st energy level. O has 2 vacancies in the
2nd energy level. Nitrogen has 3 vacancies and Carbon has 4.
~ What can reactive /unstable atoms do to become
nonreactive /stable? (Recall that a stable atom has a fully
filled outer energy level.)
Exception: for hydrogen, the Duet rule applies (only
2 electrons are needed in the valence level) They can interact with other atoms by gaining, losing or sharing
electrons to complete the atom’s valence energy level.
The main type of bond that we will study in the unit is the
covalent bond.
Only reactive atoms are able to form bonds.
The reactivity of an atom depends upon the arrangement of
electrons in its outmost (or valence) energy level.
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*Covalent Bonds
 Formed when nonmetal atoms bond with each other
 A bond in which moving electrons actually travel
about the nuclei of two atoms (at the same time)
 Electrons are shared between two atoms
Example 1:
Water (H2O)
Example 2:
Methane (CH4)
Single Covalent Bond: atoms share 2 electrons (1 pair)
Double Covalent Bond: atoms share 4 electrons (2 pairs)
Triple Covalent Bond: atoms share 6 electrons (3 pairs)
*Molecule: the structure that results when atoms are
joined together by covalent bonds. The smallest unit of
most compounds.
NOTE: Bonds between the biologically important atoms
H, O, N, C, & P (all non-metals) will be covalent.
Hydrogen will only form Covalent Bonds!!
H O N C
1 2 3 4
Molecules can also be represented by Structural
Formulas: a drawing that shows the arrangement of atoms
in a molecule
Structural Formulas tell you:
a) the types of elements in the molecule
b) the number of atoms of each element AND
c) the arrangement of atoms and location of covalent
bonds. Shows the two dimensional shape of the
molecule.
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NOTE: Structural formulas usually represent covalent
bonding so they are used for molecules like H2O, but not
for formula units like NaCl.
In a structural formula, each line between atoms represent
a position in which electrons are shared. Therefore, a line
represents a single covalent bond.
2) Ammonia or NH3
__1___ atoms of Nitrogen in the molecule
__3___ atoms of Hydrogen in the molecule
1) Hydrochloric Acid (Hydrogen Chloride) or HCl
H
___1__ atoms of Hydrogen in the molecule
___1__ atoms of Chlorine in the molecule
N–H
H
H - Cl
3) Oxygen gas or O2
4) Carbon Dioxide or CO2
___2__ atoms of Oxygen in the molecule
__1___ atoms of Carbon in the molecule
__2___ atoms of Oxygen in the molecule
O = O
O = C = O
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2.4 Chemical Reactions
Note: We will not be discussing Enzymes in this unit.
The numbers and types
of atoms in the
__reactants___
=
The numbers and types
of atoms in the
__products___
*Chemical Reactions: process that changes or transforms
one set of chemicals into another set of chemicals. Involves
changes to the chemical bonds that join atoms in
compounds.
Bonds of the reactants are broken and new bonds form in
the products.
*Reactants: elements or compounds that enter into a
chemical reaction
*Products: elements or compounds produced by a
chemical reaction
HINT: Reactants react to produce products!
Use the chemical formulas below to determine how many
atoms of each element make up each compound.
A coefficient indicates the number of molecules present.
(coefficient X subscript = the number of atoms)
*Chemical Equations: a mathematical representation of a
chemical reaction. It shows the numbers and types of
compounds involved.
*The Law of Conservation of Matter: matter (atoms and
elements) in a chemical reaction cannot be created nor
destroyed. Only the arrangement of the atoms is changed,
NOT the number or types.
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Consider the following chemical equation for cellular respiration:
In the diagram below, fill in the terms “products” or “reactants” in the proper blanks.
6O2
+
C6H12O6

Reactants
C – 6, H – 12, O – 18
6CO2
+
6H2O
Products
C – 6, H – 12, O – 18
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