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Structure of Molecules and Compounds
Complex carbon-based molecules form the basis for life on Earth.
Carbon atoms.
Carbon atoms bond in multiple patterns, forming structures with widely varying properties such as graphite and
diamond.
National Institute of General Medical Sciences/NIH.
Topics Covered in this Module
Chemical Bonds
Organic Chemistry
Major Objectives of this Module
Distinguish between molecules and compounds.
Explain what intermolecular forces are.
Relate the importance of chemical bonds and chemical reactions to life processes.
Describe the properties of carbon that allow it to form organic molecules.
Summarize the Miller-Urey experiment and explain its significance.
page 24 of 989
4 pages left in this module
Principles of Biology
5 Structure of Molecules and Compounds
We all recycle components in our trash, and our society, as a whole, is quite
aware of the importance of re-using materials. Interestingly, Earth also
recycles and reuses materials on the planet's surface. Carbon is an example
of an element that Earth recycles via a set of chemical reactions known
collectively as the carbon cycle. Carbon is an especially important element
because it is the primary building block of all life on the planet. The carbon
cycle moves carbon molecules between carbon dioxide gas (CO2) and a
wide variety of organic compounds. Organic compounds contain carbon and
hydrogen and may contain other elements as well. What exactly is carbon
and why is it so versatile? The answer lies in its molecular structure.
Chemical Bonds
Look around. What is everything made from? All the materials on Earth are
made up of the 92 naturally occurring elements. An element is a substance
that cannot be reduced to simpler substances by chemical reactions. An
atom is the smallest unit of matter that retains the properties of the element.
Elements combine in different ways. A compound is two or more elements
that combine in a fixed ratio.
Compounds are held together by chemical bonds. Chemical bonds form
because a full valence shell is more stable than a partly filled one. The
valence shell is the outermost electron shell in an atom. Atoms gain, lose or
share electrons to achieve a full valence shell. There are several types of
chemical bonds that are important in biological organisms: covalent bonds,
ionic bonds, hydrogen bonds, and van der Waals forces are ones we will
discuss here.
The bonds vary in their strength, that is, in the amount of energy (in kcal/mol
or kJ/mol) required to form and break the bonds. Covalent bonds are strong,
with free energies of 30 to 200 kcal/mol. Strong ionic bonds, such as those in
a salt lattice like NaCl also have bond energies in the same range. At
physiological temperatures, these types of bonds do not break easily. Strong
bonds often co-exist with a variety of weak bonds, like hydrogen bonds, van
der Waals forces, and weak electrostatic forces. These weak forces are
usually intermolecular forces, holding different molecules together. At
physiological temperatures, individual weak bonds are transient, with
energies in the range of 1 to 7 kcal/mol. But when many weak bonds occur
together, the bond energies are additive and result in a significant force that
is difficult to break. These properties of weak bonds — individually weak but
strong in the aggregate — are absolutely essential for life on Earth.
Covalent bonds.
A covalent bond forms when two non-metals share electrons. Non-metals
have a valence shell that is at least half full but not completely filled.
Non-metals tend to gain electrons to achieve a full valence shell. Water
(H2O) contains two hydrogen atoms and an oxygen atom. Hydrogen has one
electron in the first valence shell and needs one more to fill it because the
first valence shell holds only two electrons. Therefore, hydrogen has a
tendency to share one electron. Oxygen has six valence electrons and
needs eight. Therefore, oxygen has a tendency to share two electrons. In the
water molecule, each hydrogen atom shares a pair of electrons with the
oxygen (Figure 1). This sharing of electrons allows all three atoms to achieve
a full valence shell. Two or more atoms covalently bonded together form a
molecule.
contents
Figure 1: Three types of diagrams depicting common biological
molecules.
A molecular formula indicates the number of atoms in a molecule. A
structural formula shows the arrangement of atoms, and an electronsharing diagram depicts how electrons are shared in the covalent bonds.
© 2014 Nature Education All rights reserved.
Figure Detail
Test Yourself
What is the relationship between a compound and a molecule?
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Covalent bonds come in several varieties. A single bond forms between two
atoms that share one pair of electrons. Consider the element carbon. It has
four valence electrons. Carbon requires four additional electrons to reach a
stable configuration. It can gain these electrons, for example, by combining
with four hydrogen atoms. Each hydrogen atom has one electron in its outer
shell and requires one electron to reach a stable configuration. The carbon
atom shares one electron with each hydrogen atom, forming four covalent
single bonds. This pattern of bonding results in the methane molecule (CH4).
A double bond forms between two atoms that share two pairs of electrons.
Consider oxygen gas, which exists as the molecule O2 (Figure 1). Each
oxygen atom needs two more electrons to achieve a full valence shell. If only
a single bond were formed, each atom would gain only one electron, for a
valence of seven. Instead, the two oxygen atoms form a double bond, and so
share two electrons to each achieve a full valence shell.
Electronegativity is the ability of an atom to attract electrons. The greater
the electronegativity, the more attraction an atom has for electrons.
Electronegativity increases across the periodic table. Two non-metals with
similar electronegativity share electrons equally. The result is a nonpolar
covalent bond. In oxygen gas (O2), the bond between the two oxygen
atoms is nonpolar covalent.
When two atoms covalently bonded together have different
electronegativities, the electrons are more closely associated with the atom
with the greater electronegativity. As a result, the more electronegative atom
has a partial negative charge, and the less electronegative atom has a partial
positive charge. In such cases, a polar covalent bond forms between the
two atoms. Water is an example of a molecule with polar covalent bonds.
The oxygen atom is more electronegative than the hydrogen atoms;
therefore, it draws the electron cloud closer to its nucleus. This produces a
net negative charge over the oxygen atom and a net positive charge over the
hydrogen atoms.
Ionic bonds.
An ionic bond forms between a non-metal and a metal. A metal has a
valence shell that is less than half full. Metals tend to lose electrons to empty
the valence shell. In an ionic bond, one or more electrons are transferred
from a metal to a non-metal. The non-metal acquires a negative charge,
becoming an anion. The metal acquires a positive charge, becoming a
cation. The result is an ionic compound. An ionic compound is held
together by ionic bonds — the electrostatic attraction between the negatively
charged anions and positively charged cations. An ionic compound is also
called a salt.
Is the salt used in food an ionic compound? Yes: table salt (NaCl), also
called sodium chloride, is a common ionic compound. Chlorine has seven
valence electrons and a high electronegativity. Sodium has one valence
electron and low electronegativity. The chlorine atom strips the electron from
the sodium, producing oppositely charged ions (Figure 2) that form an ionic
compound.
Figure 2: Ionic bonding.
In sodium chloride, or table salt, an ionic bond forms when an electron is
transferred from sodium to chorine.
© 2014 Nature Education All rights reserved.
Non-covalent attractions between molecules are called intermolecular
forces. There are several different types of intermolecular forces. We will
describe two of them: hydrogen bonds and van der Waals forces.
Hydrogen bonds.
In polar covalent molecules one end of the molecule has a partial positive
charge, and the other end has a partial negative charge (Figure 3a). As a
result of the uneven charge distribution, each molecule behaves like a tiny
magnet. Like the opposite poles of magnets, the opposite poles of polar
covalent molecules are attracted to one another. A hydrogen bond occurs
when molecules that have hydrogen covalently bonded to oxygen, nitrogen
or fluorine interact. For example, water is held together by hydrogen bonds
that occur between the oxygen of one water molecule and a hydrogen on
another (Figure 3b). As we will see in later modules, hydrogen bonds are
extremely important in maintaining the double-helical structure of DNA and
the structures of proteins.
Figure 3: Hydrogen bonding.
a) In the water molecule, the shared
electrons (represented by the blue
arrows) are more closely associated
with the oxygen atom than with the
hydrogen atoms due to oxygen's higher
electronegativity. Because of the water
molecule's bent shape and its atoms'
unequal sharing of electrons, it has
partial positive (δ+) and partial negative
(δ-) poles. b) The partially positive
charge of the hydrogen on one
molecule is attracted to the partially
negative charge of the oxygen on
another, forming a hydrogen bond.
© 2012 Nature Education All rights
reserved.
van der Waals forces.
The electrons around an atom are in constant motion. Thus, the charge
around an atom fluctuates with time. At any instant, the distribution of charge
around an atom is not completely symmetric. This asymmetry of charge is
very small but strong enough to affect the charge distribution around nearby
atoms. This complementary redistribution of charge causes the neighboring
atoms to attract one another, a force that is called a van der Waals
interaction. Geckos benefit from van der Waals interactions. The hair-like
setae on their feet can interact with a wall at a molecular level to form
temporary, weak bonds. This interaction allows a gecko to walk up walls and
even on vertical surfaces as smooth as glass (Figure 4).
Figure 4: Gecko feet.
Millions of hair-like setae on the feet of geckos allow these animals to
climb smooth glass walls. Van der Waals forces adhere the setae to the
surface.
(Top) Volker Steger/Science Source. (Bottom) Eye of Science/Science
Source.
Test Yourself
What is the difference between weak and strong bonds and how do each of these bonds form?
Submit
Chemical reactions.
A chemical reaction occurs when chemical bonds are made or broken,
changing a substance's composition. Many chemical reactions occur when
you bake a cake. A cake requires a specific number of ingredients mixed
together in the correct proportions. Reactants are the ingredients in a
chemical reaction. The reactants in a cake may include flour, sugar, butter,
and eggs. In a chemical reaction, the ingredients are elements or
compounds. The reactants combine during the chemical reaction to form the
product. In the cake analogy, the product is the cake. In a chemical reaction,
the reactants and product may be a solid, a liquid or a gas.
What is an example of a chemical reaction in living organisms? Plants
perform photosynthesis, a multi-step chemical reaction. In essence, a plant
takes carbon dioxide from the air and water from the soil. The plant then
uses energy from sunlight to form a more complex molecule, glucose, using
the chemical reaction shown below. Glucose provides the plant with energy
to fuel cellular processes.
6CO2 + 6H2O → C6H12O6 + 6O2
Chemical reactions can occur in the forward and reverse directions. The
overall chemical reaction for cellular respiration, shown below, is the reverse
of the chemical reaction for photosynthesis. Respiration is a process used by
both plants and animals to extract energy from the chemical bonds that hold
glucose (C6H12O6) together. However, both processes are complex,
multi-step reactions that involve different intermediate steps. The products of
respiration, CO2 and H2O, cycle back into the environment, feeding
ultimately back into the process of photosynthesis.
C6H12O6 + 6O2 → 6CO2 + 6H2O
When the rate of a forward reaction equals the rate of its reverse reaction,
the reaction has reached chemical equilibrium.
IN THIS MODULE
Chemical Bonds
Organic Chemistry
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
The Climate Connection
How is life on Earth reacting to
climate change?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
PRIMARY LITERATURE
How elevated carbon dioxide
levels affect coral reefs
Losers and winners in coral reefs
acclimatized to elevated carbon dioxide
concentrations.
View | Download
Synthetic solanoeclepin A can
defeat crop pests
Total synthesis of solanoeclepin A.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Classic paper: The idea of the DNA
double helix (1953)
Molecular structure of nucleic acids.
View | Download
Man-made leaves may solve
energy crisis
A renewable amine for photochemical
reduction of CO2.
View | Download
SCIENCE ON THE WEB
ChemEd DL
Interact with molecular models: Rotate them
and look at their bond angles
Be a Scientist, Meet a Scientist
See if you can create organic matter with
this simulation and watch a video of Stanley
Miller
How Small?
See the difference between a coffee bean
and a single atom.
page 25 of 989
3 pages left in this module
Principles of Biology
5 Structure of Molecules and Compounds
Organic Chemistry
Carbon's chemical properties make it uniquely suited as the basis for all of
life. Because a carbon atom has four electrons in its outer shell, it can form
connections with four other atoms. Many carbons linked together can form
an endless variety of molecules. Carbon can form double as well as single
bonds. This greatly increases the variety of molecules that can be formed
using carbon. A great variety of carbon-based compounds, called organic
compounds, are needed for life as we know it. All organic compounds
contain both carbon and hydrogen. Most organic compounds in living
organisms also contain other elements, including oxygen, nitrogen,
phosphorus and sulfur. Organic chemistry focuses on the study of organic
compounds.
Organic compounds arise when carbon, hydrogen and often times other
atoms form covalent bonds among themselves. An organic compound
composed of only hydrogen and carbon is a hydrocarbon. The hydrocarbon
skeleton can exist in a variety of arrangements, including straight, branched,
and ring configurations (Figure 5).
contents
Figure 5: Altering carbon-carbon bonding within a hydrocarbon
produces different organic compounds.
The molecule pentane contains five carbons, which can be numbered
from left to right (or right to left). Each carbon can form a maximum of four
bonds. Changing the number of carbons in the chain, changing the
branching arrangement of the carbon chain, introducing double or triple
bonds, and creating ring compounds all produce new hydrocarbons with
unique names. The numbers within the name of the altered molecules
refer to the carbons that have attached chain branches or multiple bonds.
© 2012 Nature Education All rights reserved.
Figure Detail
Carbon's unique bonding properties allow complex structures to form around
the carbon atom. Isomers are compounds with the same number of atoms
of the same elements configured in different structures (Figure 6). Receptors
and enzymes can recognize particular isomers; many life processes depend
on their preference for one isomer over another.
Structural isomers differ in the arrangement of atoms between two molecules
that have the same chemical formula. With organic structural isomers the
difference is in the arrangement of atoms around the carbon chain. Because
carbon chains may be straight or branched, many different arrangements are
possible. In Figure 6a, septane and 3-methylhexane are examples of
structural isomers.
isomers differ in the spatial arrangement of atoms around the
inflexible, flat covalent double bond. In Figure 6b, cis-2-butene and trans2-butene are examples of cis-trans isomers.
Cis-trans
Enantiomers are mirror-image isomers that differ in shape due to an
asymmetric carbon atom. In Figure 6c, D-alanine and L-alanine are
examples of enantiomers.
Figure 6: Examples of structural isomers, cis-trans isomers and
enantiomers are shown.
(a) Structural isomers possess the same number and type of atoms, but
the atoms are bonded together in a different arrangement. (b) Cis- and
trans- isomers differ in how the atoms are arranged around a double bond.
In the cis- form, two similar groups are on the same side of the bond, while
in the trans- form, the similar groups are on opposite sides of the bond. (c)
Enantiomers are isomers where one molecule is a mirror image of the
other.
© 2014 Nature Education All rights reserved.
Figure Detail
BIOSKILL
Interpret Different Types of Molecular Models
How can we describe or illustrate molecules? They have a physical form
derived from the specific spatial relationships of multiple chemical elements.
Knowing what those elements are is one thing, but knowing how they are
arranged, and in what proportions, is the basis for creating molecular
models.
Figure 7: Molecular models.
Explore how molecules can be modeled in different ways.
© 2014 Nature Education All rights reserved.
Figure Detail
BIOSKILL
Functional groups.
Organic molecules often contain functional groups. A functional group is an
arrangement of atoms that together have specific chemical properties, which
they impart to the entire molecule. Functional groups are often involved in
chemical reactions. There are several common functional groups in
biological organisms (Figure 8).
Amino
Carbonyl
Carboxyl
Hydroxyl
Phosphate
Sulfhydryl
Figure 8: Functional groups.
Hydroxyl, carbonyl, carboxyl, amino, sulfhydryl and phosphate groups are
functional groups that are common in the organic molecules found in living
organisms. "R" represents the rest of the molecule bonded to the
functional group.
© 2014 Nature Education All rights reserved.
Figure Detail
Polymers.
A polymer is a long molecule consisting of many similar or identical building
blocks linked by covalent bonds. The repeating units that are used to build a
polymer are called monomers. Examples of polymers include
polysaccharides, proteins and nucleic acids (Figure 9).
Figure 9: DNA is a type of nucleic acid, which is a polymer.
(a) The monomers of DNA are the four deoxyribonucleotides, dATP,
dGTP, dCTP, and dTTP. The monomers are shown schematically. (b) A
short section of the DNA polymer is shown. The backbone, shaded in
blue, is made of repeating sugars and phosphates. The unique element of
each monomer, the nitrogenous bases, point away from the backbone. (c)
A segment of DNA is shown as a ribbon, illustrating the double helix of
DNA that forms spontaneously because the bases (A, G, C, and T) on
opposite strands hydrogen bond to one another.
© 2014 Nature Education All rights reserved.
Polymers are essential for life. But how did they arise? To answer that
question requires asking a more fundamental question: How did life arise?
Scientists and non-scientists alike have long wondered how life arose. In
1953, Harold Urey and his graduate student Stanley Miller developed an
experiment demonstrating that, under certain conditions, complex organic
compounds could form from basic chemicals, including water (H2O),
methane (CH4), ammonia (NH3) and hydrogen (H2). They used a closed
system of interconnected chemistry glassware (Figure 10). In this closed
system, a beaker of water simulated the ocean. The water was heated to
produce water vapor, which interacted with CH4, NH3, and H2 gases in a
simulated atmosphere. An electrode discharged electricity into the gases,
simulating a lightning strike. The water vapor cooled and condensed into
"rain" and re-entered the simulated ocean.
After a period of time, Miller analyzed samples of the simulated ocean water
(Figure 11). He found simple organic compounds, such as formaldehyde and
hydrogen cyanide, as well as more complex organic molecules, such as
amino acids. The finding of amino acids was particularly significant because
amino acids are the building blocks of proteins.
Figure 10: Apparatus of the Miller-Urey experiment.
Stanley Miller and his graduate adviser, Harold Urey, developed this
apparatus to simulate the oceanic and atmospheric conditions that may
have been prevalent when life began. They first placed salt water into the
oceanic bulb. Next, all air was suctioned from the apparatus through the
vacuum connection and replaced with a mixture of hydrogen gas (H2),
methane (CH4), and ammonia (NH3).
© 2012 Nature Education All rights reserved.
Figure Detail
Figure 11: Can early Earth conditions produce amino acids?
Applying heat to the oceanic bulb produces water vapor. The vapor enters
the atmospheric bulb, completing the mixture of early atmospheric gases.
After the atmospheric mixture is exposed to an electrical discharge, it
enters the cooled condenser tube. There the gases condense into liquid
"rain" that returns to the oceanic bulb. After running the experiment
continually for one week, Miller and Urey observed the oceanic water
acquire a reddish coloration. They found several amino acids in the
oceanic water that were not present previously. These included aspartic
acid, glycine, and both enantiomers of alanine.
© 2014 Nature Education All rights reserved.
Figure Detail
Controversy.
The gases used in the Miller-Urey experiment simulated what researchers
believed at the time of the experiment were the gases in Earth's early
atmosphere. Today, scientists believe that Earth's early atmosphere was
quite different from that simulated in the Miller-Urey experiment. However,
some scientists speculate that the Miller-Urey conditions might have
occurred in certain locations, including near volcanoes or deep sea
hydrothermal vents. If so, organic compounds necessary to produce life
could have formed in these isolated locations.
Researchers have also examined how a meteor impact in the ocean could
generate the conditions necessary for life to form on the planet. Scientists
performed shock compression experiments to try to recreate these
conditions. The researchers determined that simple products, like carbon,
water, gaseous nitrogen, and metals, could produce complex organic
molecules, like carboxylic acids, amines, and hydrocarbons.
Another group of researchers propose that complex organic molecules, and
perhaps life itself, did not form on Earth. Instead, these molecules arrived on
the planet in comets. Scientists created computer models to simulate how
the starting products, like water, methane, ammonia, carbon monoxide, and
carbon dioxide, would react to the shock of an impact collision. The models
predicted the creation of organic molecules, including molecules with carbonnitrogen bonds, which are required for amino acid production.
The origin of life on Earth remains an area of strong scientific interest.
Scientists continue to find new ways to assemble the basic building blocks of
life proposed in the Miller-Urey experiment. Each approach yields new
explanations for how life began on Earth. Scientists debate these ideas in an
effort to solve this ancient riddle.
Test Yourself
How did the Miller-Urey experiment energize scientists to continue the study of the
development of life on young Earth?
Submit
IN THIS MODULE
Chemical Bonds
Organic Chemistry
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
The Climate Connection
How is life on Earth reacting to
climate change?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
PRIMARY LITERATURE
How elevated carbon dioxide
levels affect coral reefs
Losers and winners in coral reefs
acclimatized to elevated carbon dioxide
concentrations.
View | Download
Synthetic solanoeclepin A can
defeat crop pests
Total synthesis of solanoeclepin A.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Classic paper: The idea of the DNA
double helix (1953)
Molecular structure of nucleic acids.
View | Download
Man-made leaves may solve
energy crisis
A renewable amine for photochemical
reduction of CO2.
View | Download
SCIENCE ON THE WEB
ChemEd DL
Interact with molecular models: Rotate them
and look at their bond angles
Be a Scientist, Meet a Scientist
See if you can create organic matter with
this simulation and watch a video of Stanley
Miller
How Small?
See the difference between a coffee bean
and a single atom.
page 26 of 989
2 pages left in this module
Principles of Biology
5 Structure of Molecules and Compounds
Summary
Distinguish between molecules and compounds.
A compound is composed of two or more different elements in a fixed ratio. A
molecule is composed of two or more non-metals that share electrons in a
covalent bond. An ionic compound forms when a non-metal takes one or
more electrons from a metal.
OBJECTIVE
Explain what intermolecular forces are.
Intermolecular forces are interactions between molecules. Hydrogen bonds
occur between molecules in which a hydrogen is covalently bonded to
oxygen, nitrogen or fluorine. The partial positive charge on the hydrogen
attracts the partial negative charge on the oxygen, nitrogen or fluorine on a
second molecule. Since hydrogen has low electronegativity and nitrogen,
fluorine and oxygen have high electronegativity, the interaction is particularly
strong. Van der Waals interactions between molecules and atoms occur due
to the asymmetric distribution of electrons in their outer shells.
OBJECTIVE
Relate the importance of chemical bonds and chemical
reactions to life processes.
Chemical bonds and chemical reactions are essential for life processes.
Chemical bonds form molecules such as DNA, amino acids, and proteins
that are required for life structure and function. Chemical reactions are the
processes by which essential materials are formed and broken down.
OBJECTIVE
Describe the properties of carbon that allow it to form organic
molecules.
Carbon atoms form the basis for all life on the planet. Carbon has four
valence electrons, which means it can form four bonds. These four bonds
allow complex molecules to form, including straight and branched chains and
rings. Single bonds have a tetrahedral shape, and double bonds have a flat
shape, so organic molecules exhibit incredible diversity.
OBJECTIVE
Summarize the Miller-Urey experiment and explain its
significance.
The Miller-Urey experiment produced complex organic compounds from
inorganic compounds. The scientists' goal was to mimic early Earth
conditions to understand how life first formed. The experiments showed that,
under certain conditions, inorganic compounds could react to form amino
acids and hydrocarbons. However, scientists now believe that Earth's early
atmosphere was very different from the one simulated in the Miller-Urey
experiment. Many scientists continue research to explain how life could have
formed on Earth.
OBJECTIVE
Key Terms
anion
Atom that has gained an electron, resulting in a net negative charge.
cation
Atom that has lost an electron, resulting in a net positive charge.
chemical bond
The attraction between atoms resulting from the sharing of electrons or the
transfer of electrons.
chemical equilibrium
contents
Balance achieved when the forward reaction of the reactants equals the reverse
reaction of the products.
chemical reaction
Change of a substance's composition by making or breaking chemical bonds
between component atoms or molecules.
compound
Two or more elements that are chemically combined in a specific ratio.
covalent bond
Type of bond that occurs between non-metals in which electrons are shared.
double bond
Covalent bond involving two pairs of electrons, with two electrons from each atom.
electronegativity
The relative strength of the attraction between an atom and an electron.
functional group
A part of a molecule that is often directly involved in a chemical reaction.
hydrocarbon
Organic compound composed of only hydrogen and carbon.
hydrogen bond
Intermolecular force that occurs between molecules in which hydrogen is
covalently bonded to oxygen, nitrogen or fluorine. The slight positive charge on
the hydrogen of one molecule interacts with the slightly negative charge on the
nitrogen, oxygen or fluorine of another molecule.
intermolecular force
An attraction between two molecules.
ion
An atom or molecule that has gained or lost electrons and thus carries a charge.
ionic bond
A bond in which one or more electrons are transferred from a metal to a
non-metal.
ionic compound
A metal and a non-metal joined by an ionic bond; also defined as a salt.
isomer
A compound that shares the same number and type of atoms as another
compound, but the arrangement of atoms is different.
metal
An element with a valence shell that is less than half full. Metals, found on the left
two-thirds of the periodic table, tend to lose electrons.
molecule
Two or more non-metals joined with a covalent bond.
monomer
A small molecule that can be joined to many similar or identical molecules to form
a long polymer.
non-metal
An element with a valence shell that is at least half full but not completely filled.
Non-metals, found on the right third of the periodic table, tend to gain or share
electrons.
nonpolar covalent bond
Covalent bond between atoms with similar electronegativity; also defined as the
bond between atoms that share electrons equally.
organic chemistry
Branch of chemistry focused on compounds containing carbon and hydrogen.
organic compound
A molecule containing carbon and hydrogen.
polar covalent bond
Covalent bond between atoms with different electronegativities; also defined as
the bond between atoms that share electrons unequally.
polymer
Long molecular chain consisting of many similar or identical building blocks
(monomers) linked by covalent bonds.
product
The result of a chemical reaction. A reaction may have one or more products.
reactant
An ingredient in a chemical reaction. A reaction may have one or more reactants.
salt
Ionic compound; also defined as the result of a bond between a metal and a
non-metal.
single bond
Covalent bond involving a single pair of electrons, one from each atom.
valence
The number of electrons in an atom's outermost electron shell.
van der Waals interaction
An intermolecular force that attracts molecules together due to the asymmetric
distribution of electrons.
IN THIS MODULE
Chemical Bonds
Organic Chemistry
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
The Climate Connection
How is life on Earth reacting to
climate change?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
PRIMARY LITERATURE
How elevated carbon dioxide
levels affect coral reefs
Losers and winners in coral reefs
acclimatized to elevated carbon dioxide
concentrations.
View | Download
Synthetic solanoeclepin A can
defeat crop pests
Total synthesis of solanoeclepin A.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Classic paper: The idea of the DNA
double helix (1953)
Molecular structure of nucleic acids.
View | Download
Man-made leaves may solve
energy crisis
A renewable amine for photochemical
reduction of CO2.
View | Download
SCIENCE ON THE WEB
ChemEd DL
Interact with molecular models: Rotate them
and look at their bond angles
Be a Scientist, Meet a Scientist
See if you can create organic matter with
this simulation and watch a video of Stanley
Miller
How Small?
See the difference between a coffee bean
and a single atom.
page 27 of 989
1 pages left in this module
Principles of Biology
contents
5 Structure of Molecules and Compounds
Test Your Knowledge
1. What type of chemical bond is found in the methane molecule?
covalent single bond
covalent double bond
covalent triple bond
ionic bond
None of the answers are correct.
2. Which element is present in all organic compounds?
nitrogen
carbon
oxygen
sulfur
phosphorus
3. Why is carbon capable of forming single and double bonds?
It has four valence electrons.
It has one valence electron.
It has two valence electrons.
It has three valence electrons.
None of the answers are correct.
4. Which of the following is an outcome of the Miller-Urey experiment?
It showed that complex organic compounds could form spontaneously from
inorganic compounds.
It caused biologists to view natural phenomena in terms of physical and chemical
laws.
It raised considerable controversy that prompted additional scientific inquiry.
Scientists began to propose alternative theories to explain how organic molecules
formed and how life came into existence.
All answers are correct.
5. What would have to happen in order for a polar covalent bond to form?
One atom would have to share electrons equally with another atom.
One atom would have to donate an electron to another atom.
One atom would have to share electrons unequally with another atom.
One atom would have to accept an electron from another atom.
One atom would have to act as a cation and another would have to act as an
anion.
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IN THIS MODULE
Chemical Bonds
Organic Chemistry
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
The Climate Connection
How is life on Earth reacting to
climate change?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
PRIMARY LITERATURE
How elevated carbon dioxide
levels affect coral reefs
Losers and winners in coral reefs
acclimatized to elevated carbon dioxide
concentrations.
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Synthetic solanoeclepin A can
defeat crop pests
Total synthesis of solanoeclepin A.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Classic paper: The idea of the DNA
double helix (1953)
Molecular structure of nucleic acids.
View | Download
Man-made leaves may solve
energy crisis
A renewable amine for photochemical
reduction of CO2.
View | Download
SCIENCE ON THE WEB
ChemEd DL
Interact with molecular models: Rotate them
and look at their bond angles
Be a Scientist, Meet a Scientist
See if you can create organic matter with
this simulation and watch a video of Stanley
Miller
How Small?
See the difference between a coffee bean
and a single atom.
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