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MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 17: COVALENT BONDING AND BIOCHEMISTRY
COVALENT BONDING CLASS NOTES
COVALENT COMPOUNDS
Covalent compounds form when pairs of electrons are shared between atoms. Covalent compounds are
usually called molecules.
COVALENT BONDS
Hydrogen and helium (atomic numbers 1 and 2) follow the duet rule of bonding because they only hold
two electrons. Elements 3 – 18 follow the octet rule because they share electrons to obtain eight valence
electrons.
Example 1. Two hydrogen and one oxygen atom combine to form water. Complete the following steps
to construct an LDS diagram for the water molecule.
1a. Draw LDS diagrams for hydrogen and oxygen.
A.
1b. Show the sharing of electrons to form the water molecule.
A.
1c. Draw the LDS diagram for water.
A.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
Example 2. Four hydrogen and one carbon combine to form methane (CH4). Complete the following
steps to construct an LDS diagram for the methane molecule.
2a. Draw LDS diagrams for carbon and hydrogen.
A.
2b. Show the sharing of electrons to form the methane molecule.
A.
2c. Draw the LDS diagram for methane.
A.
STRUCTURAL DIAGRAMS
Lines can be drawn instead of dots between atoms to represent covalent bonds. These are called
structural diagrams.
Example 3. Draw the structural diagram for methane.
3A. As seen in Example 2, the LDS diagram for methane is:
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MR. SURRETTE
VAN NUYS HIGH SCHOOL
3A. (continued…)
Since the central carbon atom shares one pair of electrons with each of the hydrogen atoms, the
structural diagram for methane is:
Example 4. Two hydrogen atoms combine to form the hydrogen molecule. Draw the structural
diagram for H2.
4A. Both hydrogen atoms have a single electron. When they combine to form the hydrogen molecule,
they share these two electrons. This creates a single covalent bond between them. The structural
diagram for H2 is:
COVALENT BOND STRUCTURE
Atoms that share a pair of electrons create a single covalent bond. Atoms can also combine to form
multiple bonds. For example, atoms that share four electrons create double bonds, and atoms that share
six electrons create triple bonds.
Example 5. Two oxygen and one silicon atom combine to form silicon dioxide. Complete the
following steps to construct a structural diagram for SiO2.
5a. Draw LDS diagrams for silicon and oxygen.
5b. Show the sharing of electrons to form SiO2.
A. Notice the two lines drawn around each oxygen atom shown below. These lines represent valence
electrons already paired up and unavailable for bonding.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
5b. (continued…)
The green circles represent orbital spaces that can accept electrons:
5c. Draw the LDS diagram for SiO2.
A.
5d. Draw the structural diagram for SiO2.
A.
Example 6. Two nitrogen atoms combine to form the nitrogen molecule. Complete the following steps
to construct a structural diagram for N2.
6a. Draw the LDS diagram for nitrogen.
A.
6b. Show the sharing of electrons to form N2.
A.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
6c. Draw the LDS diagram for N2.
A.
6d. Draw the structural diagram for N2.
A. Notice the triple bonds between the nitrogen atoms:
COVALENT BOND LENGTHS
The distance between atoms in a compound is called bond length. In covalent compounds, the bond
length is proportional to the number of bonds between atoms. Single covalent bonds have the greatest
bond lengths. Double covalent bonds are a little shorter, and triple covalent bonds are the shortest.
METALS (re-visited)
The outer electrons of metal atoms are weakly held to the atomic nucleus. As a result, these outer
electrons are easily removed, leaving behind positively charged metal ions.
METALLIC BONDS
Electrons removed from a large group of metal atoms flow freely through the metal ions. This “fluid” of
electrons holds the positively charged metal ions together. This is the metallic bond.
METALLIC BONDS
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 17: COVALENT BONDING AND BIOCHEMISTRY
BIOCHEMISTRY CLASS NOTES
THE CARBON ATOM
The fundamental atom composing organic compounds is carbon. Carbon can form large molecules in
limitless varieties because carbon has the ability to bond covalently in four directions to other atoms.
CARBON BONDING
Carbon may form single, double, or even triple bonds. A single bond occurs when two electrons are
shared. One line is used in the structural formula. Two lines indicate the sharing of two pairs of
electrons, a double bond. Three lines represent the sharing of three pairs of electrons, a triple bond.
CARBON ATOM STRUCTURE
Carbon, like all other atoms, exists in three-dimensional space. Visualize the carbon atom sitting in the
middle of a tetrahedron (pyramid-shape). The four corners of the tetrahedron are the positions of its
electrons. Lines drawn from the central carbon to the four corners are its bonding electrons.
CARBON-BASED MOLECULES
CARBOHYDRATES
Carbohydrates are made of carbon, oxygen, and hydrogen. They include sugars, starches, cellulose,
chitin, and glycoproteins.
SUGARS
Monosaccharides – like glucose (C6H12O6) look like pentagonal or hexagonal rings. Two
monosaccharide rings may join in a reaction called dehydration synthesis. In this joining, a certain
hydroxide (HO-) group from one ring approaches a hydroxide group in another ring.
DEHYDRATION SYNTHESIS
One of the hydroxides and a hydrogen from the other hydroxide break off and join to form water. The
oxygen that is left attached to one ring bonds covalently with the exposed carbon of the other ring.
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MR. SURRETTE
VAN NUYS HIGH SCHOOL
SUGAR FORMATION
SUGARS
The bonding of two monosaccharides makes a disaccharide like sucrose (C12H22O11). These bonded
rings may go through a reverse reaction called hydrolysis where water is put back in and the rings
separate. Polysaccharides are formed as more and more rings add together.
LIPIDS
Lipids, which include oils, fats, and waxes, are large molecules used for energy storage and to coat a
surface to make it waterproof. A large part of the lipid structure consists of long chains of nonpolar,
covalently bonded carbons. They are hydrophobic and do not attract polar water molecules.
FATS
Organic acids have a carboxyl group (-COOH) at one end. Long organic acids are called fatty acids.
These acids are commonly chains of sixteen to eighteen carbons. A glycerol molecule and three fatty
acids combine by dehydration synthesis to make a fat molecule. Much more energy can be stored in a
gram of fat than in a gram of starch.
FORMATION OF FAT
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MR. SURRETTE
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PROTEINS
Proteins, polymers of amino acids, make up hair, muscle, connective tissue, enzymes, and fingernails.
An amino acid is a small molecule that has a central carbon covalently bonded to an amine group, a
carboxyl (acid) group, a hydrogen atom and an R-group.
PROTEINS
About twenty R-groups exist. Dehydration synthesis creates a peptide bond that holds two amino acids
together, making a dipeptide. A longer chain of amino acids is a polypeptide. A protein is the total
molecule.
PROTEIN FORMATION
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