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Biology
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2-1 The Nature of Matter
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Atoms
Atoms
The study of chemistry begins with the basic unit of
matter, the atom.
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Atoms
Placed side by side, 100 million atoms would make a
row only about 1 centimeter long.
Atoms contain subatomic particles that are even
smaller.
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Atoms
The subatomic particles that make up
atoms are
• protons
• neutrons
• electrons
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Atoms
The subatomic
particles in a helium
atom.
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Elements and Isotopes
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.
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Elements and Isotopes
The number of protons in an atom of an element is
the element's atomic number.
What else does the atomic number equal?
Commonly found in living organisms:
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Elements and Isotopes
Isotopes
Atoms of the same element that differ in the
number of neutrons they contain are known as
isotopes.
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Nonradioactive carbon-
12
Nonradioactive carbon-
13
Radioactive carbon-
14
6 electrons6 protons
6 neutrons
6 electrons6 protons
8 neutrons
6 electrons6 protons
7 neutrons
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Elements and Isotopes
Because they have the same number of
electrons, all isotopes of an element have
the same chemical properties.
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Elements and Isotopes
Radioactive Isotopes
Some isotopes are radioactive, meaning that their
nuclei are unstable and break down at a constant
rate over time
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Elements and Isotopes
Radioactive isotopes can be used:
• to determine the ages of rocks and fossils.
• to treat cancer.
• to kill bacteria that cause food to spoil.
• as labels or “tracers” to follow the movement of
substances within an organism.
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Chemical Compounds
Chemical Compounds
A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.
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Chemical Compounds
Chemical Formula
Water = H2O
Table Salt = NaCl
Hydrochloric Acid = HCl
Glucose = C6H12O6
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Chemical Bonds
Chemical Bonds
The atoms in compounds are held together by
chemical bonds.
The electrons that are available to form bonds are
called valence electrons.
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Chemical Bonds
The main types of chemical bonds are:
• ionic bonds
• covalent bonds
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Chemical 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.
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Chemical Bonds
Protons +17
Electrons - 18
Charge -1
Protons +11
Electrons - 11
Charge 0
Protons +11
Electrons - 1
Charge
Protons +17
Electrons - 1
Charge
Sodium ion (Cl-)Sodium atom (Na)
Pg.38 in
book
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Chemical Bonds
Covalent Bonds
Sometimes electrons are shared by atoms instead
of being transferred.
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Chemical Bonds
A covalent bond forms when electrons are shared
between atoms.
• single covalent bond
2 electrons shared
• double bond
4 electrons shared
• triple bond
6 electrons shared
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Chemical Bonds
The structure that results when atoms are joined
together by covalent bonds is called a molecule.
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Chemical Bonds
Van der Waals Forces
When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules.
Forces of attraction between molecules.
Hold large molecules together.
Allow geckos to balance the pull of gravity.
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These
synthetic
Carbon
nanotubes
make a ‘glue’
10X stickier
than a
gecko’s foot
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The particles that move around the nucleus of
an atom are called
a. neutrons.
b. protons.
c. electrons.
d. isotopes.
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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
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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.
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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.
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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.
END OF SECTION