Name
CHAPTER 11
Class
Date
The Chemistry of Living Things
SECTION
1 Elements in Living Things
California Science
Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
•
•
•
•
8.6.a, 8.6.b
What common elements make up living organisms?
Why is carbon important to living organisms?
How do carbon atoms combine with other atoms?
How do scientists use organic compounds to benefit
people?
What Elements Make Up Living Organisms?
There are over 90 elements known to exist in the universe. Yet, only a handful of elements make up most of
any organism. The most common elements that make
up living things are carbon, hydrogen, nitrogen, oxygen,
phosphorus, and sulfur. These six elements make up
more than 96% of your body weight!
Most Common Elements in the Human Body
Element
Percentage by weight
Oxygen
65.0
Carbon
18.5
Hydrogen
9.5
Nitrogen
3.3
Phosphorus
1.0
Sulfur
0.3
Other
2.4
Elements combine with one another to form particles
called molecules. There are many types of molecules in
your body. These molecules make up the billions of cells
found in your body. Your body has different types of cells.
Each kind of cell has its own purpose, and each has some
different molecules.
How do so few elements create the many different
molecules your body needs? Atoms of these elements
combine in different ways. The kinds and locations of the
elements in a molecule control how it works.
STUDY TIP
Outline As you read this
section, create an outline.
Outlining what you read can
help you remember and
organize the main ideas.
Math Focus
1. Apply Data Using your
weight, in pounds, and the
percentage carbon given
in the table, calculate the
weight of carbon in your
body. Show your work.
Critical Thinking
2. Infer Does your body need
more than six elements? If so,
can you name one or more?
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Elements in Living Things continued
Why Is Carbon Important to Living Organisms?
READING CHECK
3. Define What is an organic
compound?
READING CHECK
4. Identify How many
bonds can a carbon atom
form with other atoms?
Remember that a compound is a group of atoms
bonded together. Most of the molecules made in your
body are compounds that contain carbon atoms. These
are called organic compounds. An organic compound
is a compound in which carbon is covalently bonded to
other carbons and to other atoms. All living things contain organic compounds. Carbon is necessary for life.
There are over a million organic compounds. How can carbon be part of so many different kinds of molecules? Carbon
has a property most other elements do not have. Carbon can
bond to other carbon atoms in several different ways.
Each carbon atom has four valence electrons. So, a
carbon atom can make a total of four bonds. When carbon atoms bond with other carbon atoms, they make
what is called a carbon backbone. One type of carbon
backbone is a long straight chain. A chain can form a
ring. Finally, the carbon atoms can also form a branched
chain backbone. There are many organic compounds that
have at least one of these three basic shapes.
Three Kinds of Carbon Backbones
H
H C H
H C H
H C H
H C H
H C H
TAKE A LOOK
5. Identify What are the
three kinds of carbon
backbones?
H C H
H
Straight chain
Carbon atoms are connected one after another.
H
H C H
H
H
C
H C
H C
C
H
H
H C H H
H C
C H
H C H H
H C H
H
Branched chain
The chain of carbon atoms
branches when a carbon atom
bonds to more than two other
carbon atoms.
H
H
C
C
H
H
H
H
Ring
The chain of carbon
atoms forms a ring.
How Does Carbon Combine with Other Atoms?
SINGLE BONDS
READING CHECK
6. Describe How many
electrons are shared in a
single bond?
When a carbon atom shares only one pair of electrons
with another atom, the bond is called a single bond. In
the figure above, all bonds are single bonds. Gasoline
contains many molecules with single covalent bonds.
Gasoline is made from petroleum, from deep in Earth’s
crust. The organic compounds in petroleum are from the
remains of organisms that lived long ago.
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Elements in Living Things continued
DOUBLE BONDS
A carbon atom can also form a double bond by sharing
two pairs of electrons. A double bond is stronger than a
single bond.
Imagine that you are a carbon atom. Your two arms
and two legs are bonds that can be made when you join
to other people. If you use each hand or foot to join to
someone else, you can connect to four people. This
represents four single bonds.
However, if you hold onto another person’s arm with
both hands, then you have a stronger hold on that person.
This represents a double bond. You can still bond to two
other people with your feet.
TRIPLE BONDS
A carbon atom can form a triple bond with another
atom by sharing three pairs of electrons. A triple bond is
stronger than a double bond.
The figure below shows that the names of threecarbon compounds tell the kinds of bonds they have.
READING CHECK
7. Describe How many
electrons are shared in a
double bond?
CALIFORNIA
STANDARDS CHECK
8.6.c Students know that
carbon, because of its ability
to combine in many ways with
itself and other elements, has a
central role in the chemistry of
living organisms.
8. Identify What are the
three types of bonds that a
carbon atom can form with
another atom?
Three Types of Bonds Between Carbon Atoms
Single Bond
H H H
H C C C H
H H H
The propane in a
camping stove contains
only single bonds.
Double Bond
H
H
C C
H
H
Fruits make ethene,
which is a compound
that helps ripen the fruit.
Triple Bond
H C C H
Ethyne is better known
as acetylene. It is burned
in miners’ lamps and in
welding torches.
How Do Scientists Use Organic Compounds
to Benefit People?
When organic compounds were first discovered, scientists thought they could be made only inside living things.
However, scientists now use technology to make many
organic compounds. These include useful products such
as vitamins and medicines. Scientists are also trying to
make organic compounds to help the environment. For
example, they are trying to make fuels that don’t pollute
as much as gasoline.
TAKE A LOOK
9. Analyze Models What is
the largest number of atoms
a carbon atom can bond to
with all single bonds?
10. Analyze Models What if
one of the bonds is a double
bond?
11. Analyze Models What
if one of the bonds is a triple
bond?
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8.6.a, 8.6.b
SECTION VOCABULARY
organic compound a covalently bonded
compound that contains carbon
1. Identify What are the six most common elements found in organic compounds?
2. Analyze What properties of carbon make it important for living organisms?
3. Apply You are a chemist who has found an unknown organic compound. Your data
show the compound is made of carbon and hydrogen atoms. There are four carbon
atoms. All the bonds are single covalent bonds. Based on what you know about the
types of carbon backbones, draw the three structures possible for this compound.
4. Infer Petroleum products such as gasoline are made of compounds containing
carbon. How can you use this clue to hypothesize where petroleum originally
comes from?
5. Evaluate Name an example of an organic compound made by scientists. How is it
used to benefit people?
6. Explain How can an organic compound exist without single bonds between the
carbons?
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