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2-1 The Nature of Matter
Atoms
The study of chemistry begins with the basic
unit of matter, the atom.
Placed side by side, 100 million atoms
would make a row only about 1 centimeter
long.
Atoms contain subatomic particles that are
even smaller.
The subatomic particles that make up atoms
are
a. protons
b. neutrons
c. electrons
The subatomic
particles in a helium
atom.
Elements and Isotopes
A chemical element is a pure substance that
consists entirely of one type of atom.
–
C stands for carbon.
–
Na stands for sodium.
The number of protons in an atom of an
element is the element's atomic number.
Commonly found in living organisms:
Isotopes
Atoms of the same element that differ in the
number of neutrons they contain are known
as isotopes.
Because they have the same number of
electrons, all isotopes of an element have the
same chemical properties.
Radioactive Isotopes
Some isotopes are radioactive, meaning that
their nuclei are unstable and break down at a
constant rate over time
Radioactive isotopes can be used:
a. to determine the ages of rocks and fossils.
b. to treat cancer.
c. to kill bacteria that cause food to spoil.
d. as labels or “tracers” to follow the
movement of substances within an organism.
Chemical Compounds
A chemical compound is a substance formed
by the chemical combination of two or more
elements in definite proportions.
Chemical Formula
Water
H2O
Table Salt
NaCl
Hydrochloric Acid
HCl
Glucose
C6H12O6
Chemical Bonds
The atoms in compounds are held together by
chemical bonds.
The electrons that are available to form bonds
are called valence electrons.
The main types of chemical bonds are:
a. ionic bonds
b. covalent bonds
Ionic Bonds
An ionic bond is formed when one or more
electrons are transferred from one atom to
another.
These positively and negatively charged atoms
are known as ions.
Sodium atom (Na)
Chlorine ion (Cl-)
Sodium ion (Na+)
Chlorine atom (Cl)
Protons
Electrons
+11
- 11
10
Protons
Electrons
+17
18
- 17
Charge
+10
Charge
-10
Covalent Bonds
Sometimes electrons are shared by atoms
instead of being transferred.
A covalent bond forms when electrons are
shared between atoms.
a. single covalent bond
b. double bond
c. triple bond
The structure that results when atoms are
joined together by covalent bonds is called
a molecule.
Van der Waals Forces
When molecules are close together, a slight
attraction can develop between the
oppositely charged regions of nearby
d
molecules.
d+
d-
d+
Quiz 2-1
The particles that move around the nucleus of
an atom are called
a. neutrons.
b. protons.
c. electrons.
d. isotopes.
The atomic number of a carbon atom is 6. How
many neutrons does the isotope carbon-14
have?
a. 6
b. 8
c. 12
d. 14
Which of the following statements about the
three isotopes of carbon is true?
a. They are all radioactive.
b. They have different numbers of electrons.
c. They have the same chemical properties but
differ in atomic mass.
d. They have the same number of protons and
neutrons.
A chemical compound consists of
a. Electrons mixed with neutrons.
b. two or more elements combined in a definite
proportion.
c. two or more protons combined in any
proportion.
d. at least three elements combined by ionic or
covalent bonds.
Van der Waals forces are the result of
a. unequal sharing of electrons.
b. ionic bonds.
c. the bonding of different isotopes.
d. the chemical combination of sodium and
chlorine.
2-2 Properties of Water
A water molecule is polar because there
is an uneven distribution of electrons
between the oxygen and hydrogen atoms.
d+
d-
Hydrogen Bonds
Because of their partial positive and negative
charges, polar molecules can attract each other.
Cohesion is an attraction between molecules of the
same substance.
Because of hydrogen bonding, water is extremely
cohesive.
Adhesion is an attraction between molecules of
different substances.
Solutions and Suspensions
A mixture is a material composed of two or more
elements or compounds that are physically mixed
but not chemically combined.
Two types of mixtures can be made with water
– solutions
– suspensions
Solutions
All the components of a solution are evenly
distributed throughout the solution.
solute—the substance that is dissolved.
solvent—the substance in which the solute
dissolves.
When a crystal of table salt is placed in warm
water, sodium and chloride ions are attracted to
the polar water molecules.
Suspensions
Some materials do not dissolve when placed in
water but separate into pieces so small that they
do not settle out easily.
Acids, Bases, and pH
A water molecule is neutral, but can react to form
hydrogen and hydroxide ions.
H2O   H+ + OH-
The pH scale
Chemists devised a measurement system called
the pH scale to indicate the concentration of H+
ions in solution.
The pH scale ranges from 0 to 14.
The pH Scale
At a pH of 7, the
concentration of
H+ ions and OHions is equal.
Acids
An acid is any compound that forms H+ ions in
solution.
Bases
A base is a compound that produces hydroxide
ions (OH- ions) in solution.
Buffers
The pH of the fluids within most cells in the human
body must generally be kept between 6.5 and 7.5.
Controlling pH is important for maintaining
homeostasis.
Quiz 2-2
A molecule in which the charges are unevenly
distributed is called a
a. polar molecule.
b. cohesive molecule.
c. hydrogen molecule.
d. covalent molecule.
A dissolved substance is called a
a. solvent.
b. solution.
c. solute.
d. suspension.
A compound that produces hydroxide ions in
solution is called a(an)
a. base.
b. buffer.
c. acid.
d. salt.
Hydrogen bonds between water molecules
result from
a. adhesion between water molecules.
b. magnetic attractions between water
molecules.
c. uneven electron distribution in each water
molecule.
d. ionic bonds in the water molecule.
On a pH scale, a value of 2 means that the
solution has
a. equal concentrations of H+ and OH- ions.
b. the same concentration of H+ ions as pure
water.
c. higher concentration of H+ than in pure
water.
d. lower concentration of H+ than in pure water.
The Chemistry of Carbon
Organic chemistry is the study of all compounds
that contain bonds between carbon atoms.
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Macromolecules
Macromolecules are
formed by a process
known as polymerization.
Monomers
Polymers
Four groups of organic compounds found in
living things are:
a.carbohydrates
b.lipids
c.nucleic acids
d.proteins
Macromolecules!
What is the function of carbohydrates?
Source of Energy
Structure
Carbohydrates
Carbohydrates are compounds made up of
carbon, hydrogen, and oxygen atoms, usually in a
ratio of 1 : 2 : 1.
Different sizes of carbohydrates:
•Monosaccharides
• Glucose
•Disaccharides
• Sucrose
•Polysaccharides
• Starch
Starches and sugars are examples of
carbohydrates that are used by living things as
a source of energy.
Examples:
Cellulose
Starch
Glycogen
Starch
Glucose
Lipids
Lipids are generally not soluble in water.
The common categories of lipids are:
fats
oils
waxes
steroids
Lipids can be used to store energy. Some
lipids are important parts of biological
membranes and waterproof coverings.
Nucleic Acids
Nucleic acids are polymers assembled from
individual monomers known as nucleotides.
Nucleotides consist of three parts:
a.a 5-carbon sugar
b.a phosphate group
c.a nitrogenous base
Nucleic acids store and transmit hereditary, or
genetic, information.
ribonucleic acid (RNA)
deoxyribonucleic acid (DNA)
Proteins
Proteins are macromolecules that contain
nitrogen, carbon, hydrogen, and oxygen.
– polymers of molecules called amino acids.
The portion of each amino acid that is different is a
side chain called an R-group.
The instructions for arranging amino acids into
many different proteins are stored in DNA.
Protein
Molecule
Amino
Acids
Some functions of proteins:
–Control rate of reactions – Enzymes
–Used to form bones and muscles
–Transport substances into or out of cells
–Help to fight disease - antibodies
Quiz 2-3
Large carbohydrate molecules such as starch
are known as
a. lipids.
b. monosaccharides.
c. proteins.
d. polysaccharides.
Many lipids are formed from glycerol and
a. fatty acids.
b. monosaccharides.
c. amino acids.
d. nucleic acids.
Proteins are among the most diverse
macromolecules because
a. they contain both amino groups and carboxyl
groups.
b. they can twist and fold into many different
and complex structures.
c. they contain nitrogen as well as carbon,
hydrogen, and oxygen.
d. their R groups can be either acidic or basic.
Which of the following statements about
cellulose is true?
a. Animals make it and use it to store energy.
b. Plants make it and use it to store energy.
c. Animals make it and use it as part of the
skeleton.
d. Plants make it and use it to give structural
support to cells.
A major difference between polysaccharides and
proteins is that
a. plants make polysaccharides, while animals
make proteins.
b. proteins are made of monomers, while
polysaccharides are not.
c. polysaccharides are made of
monosaccharides, while proteins are made
of amino acids.
d. proteins carry genetic information, while
polysaccharides do not.
Chemical Reactions
A chemical reaction is a process that changes
one set of chemicals into another set of chemicals.
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The elements or compounds that enter into
a chemical reaction are known as reactants.
The elements or compounds produced by a
chemical reaction are known as products.
Energy Changes
Chemical reactions that release energy
often occur spontaneously.
Chemical reactions that absorb energy
will not occur without a source of energy.
When hydrogen gas reacts with oxygen to
produce water vapor, it is an energyreleasing reaction in which energy is given
off as heat.
2H2 + O2
2H2O
How would you reverse this reaction?
Activation Energy
Chemists call the energy that is needed to get
a reaction started the activation energy.
Enzymes
Some chemical reactions that make life possible
are too slow or have activation energies that are
too high.
These chemical reactions are made possible by
catalysts.
Enzymes are Biological Catalysts.
Enzymes speed up chemical reactions that
take place in cells.
The Enzyme-Substrate Complex
Enzymes provide a site where reactants can be
brought together to react, reducing the energy
needed for reaction.
The reactants of enzyme-catalyzed reactions are
known as substrates.
An Enzyme-Catalyzed Reaction
Regulation of Enzyme Activity
Enzymes can be affected by any variable that
influences a chemical reaction.
– pH values
– Changes in temperature
– Enzyme or substrate concentrations
Quiz 2-4
The elements or compounds produced by a
chemical reaction are known as
a. reactants.
b. enzymes.
c. products.
d. waste.
Chemical reactions always involve
a. changes in energy.
b. enzymes.
c. catalysts.
d. changes in the atomic number of the
reactants.
The factor that prevents many energy-releasing
reactions from occurring at relatively low
temperatures is called
a. catalytic energy.
b. chemical bond energy.
c. enzyme energy.
d. activation energy.
Which of the following statements is true?
a. All proteins are enzymes.
b. All catalysts are enzymes.
c. All enzymes are catalysts.
d. All catalysts are proteins.
What happens to an enzyme after the reaction it
catalyzes has taken place?
a. The enzyme is destroyed, and the cell must
make another.
b. The enzyme holds on to the product until
another enzyme removes it.
c. The enzyme is unchanged and ready to
accept substrate molecules.
d. The enzyme changes shape so it can accept
a different kind of substrate.