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Name: ___________________________
Date: ______________
Unit 2: Ecological Biochemistry
Unit 2A- Basic Chemistry
NOTES
Atoms are the Basic Units of Matter
Atoms are incredibly small. Placed side by side, 100 million atoms would make a
row only about 1 centimeter long—about the width of your little finger!
What are Atoms made of?
Atoms are made of particles called protons, neutrons,
and electrons.
 Protons have a __________________ (+) charge
 Electrons have a _________________ (-) charge
 Neutrons are ___________________ (no charge)
*Atoms normally have equal numbers of electrons and
protons, making them neutral
Elements
Elements are pure substances made of only
______________________ of atom
 Elements are listed in the periodic table of
elements
 They are arranged in order of their atomic
numbers
 An atom is the smallest unit of an element that has the properties of that
element
Summary/ Additional Notes:
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Atomic Number and Mass Number
The atomic number of an element is the number of _____________________
(typically the same as the number of electrons)
The mass number/atomic mass of an element is the number
of _______________ plus the number of _______________
 Use your periodic table to complete the following chart:
Element
Symbol
Atomic
Number
Mass
Number
Helium
He
2
4
Magnesium
Mg
12
Zinc
Zn
30
Bromine
Br
Aluminum
Al
Summary/ Additional Notes:
Number of
Protons
Numbers of
Neutrons
Number of
Electrons
2
12
65
35
80
45
13
14
35
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Important Elements for Biology
The five most abundant elements in living things are:
1. Hydrogen – 10%
2. Oxygen – 65%
3. Nitrogen – 4%
4. Carbon – 19%
5. Phosphorus – 1%
 Label the pie graph with each of the element most common in living things
Molecules, Compounds, and Chemical Formulas
A molecule is made when 2 or more of
_____________________ are joined together (Ex: O2, H2O)
A compound is a substance formed by the combination of two
or more ___________________ elements (Ex: H2O, C6H12O6)
All compounds are molecules, but not all molecules are compounds
Chemical Formula- written shorthand showing the composition of a compound
Chemical Formulas
Coefficient: tells how many
_______________________ of that substance
(the large number BEFORE the formula)
Subscript: goes with the element symbol preceding the number; tells how many
_________________ of that element within one molecule of the substance (small
number WITHIN the formula).
Summary/ Additional Notes:
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 Fill in the table
Example 2: 6CO2
What is the coefficient? _______
What is carbon’s subscript? ________
What is oxygen’s subscript? ________
How many molecules of this compound are represented by this formula?________
How many atoms TOTAL are present in this molecule? ______
Chemical Bonds
The atoms in compounds are held together by chemical bonds.
Making bonds involves the electrons that surround each
nucleus.
The electrons that are available to form bonds are called
valence electrons.
Summary/ Additional Notes:
This type of
drawing is called a
Bohr model
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Valence Electrons
The electrons of an atom are spread out in different layers
around the nucleus to make an “_________________________”
These layers are called energy levels
 2 electrons go in the first energy level
 8 electrons can go in the second energy level and beyond
(octet rule)
If there are not 8 electrons for the outer level, these empty spots
are called vacancies and some electrons are thus unpaired
The unpaired electrons in the outer layer are the valence
electrons
The valence electrons can pair with those from other atoms to
“fill” the vacancy
This creates a molecule
Water Molecule
Bohr Model vs. Lewis Dot Structure
Bohr Model: shows all
of the electrons in their
energy levels
Summary/ Additional Notes:
Lewis Dot
Structure: shows
just the valence
electrons in the outer
energy level
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 Draw a Bohr model and a Lewis Dot structure for each of the elements
listed below. Hint: you need to know the number of what to draw these?
Element
Bohr
Lewis Dot
Carbon
Nitrogen
Reactive vs. Stable
The reactivity of an atom is determined by the number of vacancies in its outer
energy level
 If there are vacancies, the atom is reactive/unstable
 If there are no vacancies, the atom is nonreactive/stable
 If the vacancies are filled due to bonding, the molecule is stable
The main types of chemical bonds are
1. ionic bonds
2. covalent bonds
There are other types of bonds and interactions but they are not as strong as these
two types
Summary/ Additional Notes:
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1. Ionic Bonds
An ionic bond is formed when one or more electrons are transferred from one
atom to another.
 An atom that loses electrons becomes positively charged.
 An atom that gains electrons has a negative charge.
 These positively and negatively charged atoms are known as ions.
 These oppositely charged ions have a strong attraction for each other,
forming an ionic bond.
2. Covalent Bonds
When electrons are shared by atoms instead of
transferred.
The moving electrons travel about the nuclei of both
atoms, forming a covalent bond.
A covalent bond can be a…
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)
Summary/ Additional Notes:
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HONC
Bonds between the most important biological atoms will be covalent
The number of bonds each can make is important for the compounds that will be
created using these atoms
H O N C
1 2 3 4
_________________________
_________________________
_________________________
Hydrogen -can form 1 single bond
Oxygen- can form 2 single bonds or one double bond
Nitrogen- can form 3 single bonds or 1 double bond and 1 single bond
Carbon- can form 4 single bonds or 2 double bonds, or 1 double bond and 2 single
bonds (no quadruple bond!)
Structural formulas
Show you…
_____________
- the types of elements in the molecule
- the number of atoms of each element
AND
- the arrangement of atoms and location of
covalent bonds. Shows the two dimensional
shape of the molecule.
_____________
Summary/ Additional Notes:
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Chemical Reactions
Chemical Reactions: process that ____________________ or transforms one set
of chemicals into another set of chemicals. Involves changes to the chemical
bonds that join atoms in compounds.
 Reactants: elements or compounds that _________ into a chemical reaction
 Products: elements or compounds ______________ by a chemical reaction
HINT: Reactants react to produce products!
*Bonds of the reactants are broken and new bonds form in the products
Chemical Equations
Chemical Equation: a mathematical representation of a chemical reaction. It
shows the numbers and types of compounds involved.
What process is this equation for? ___________________________________
6O2
+
Summary/ Additional Notes:
C6H12O6

6CO2
+
6H2O + _____
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Balancing Chemical Equations
The Law of Conservation of Matter:
matter (atoms and elements) in a chemical
reaction ____________________ be created
or destroyed. Only the arrangement of the
atoms is changed, NOT the number or
types.
Therefore both sides of a chemical equation must be “______________________”
(have the same number of atoms).
 Are these equations balanced?
C + 2H2 --> CH4
Na2SO4 + CaCl2 --> CaSO4 + NaCl
C2H6 + O2 --> CO2 + H2O
2Al2O3 --> 4Al + 3O2
Summary/ Additional Notes: