Biology
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2-1 The Nature of Matter
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2-1 The Nature of Matter
Atoms
Atoms
The study of chemistry begins with the basic unit of
matter, the atom.
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2-1 The Nature of Matter
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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2-1 The Nature of Matter
Atoms
The subatomic particles that make up
atoms are
• protons
• neutrons
• electrons
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2-1 The Nature of Matter
Atoms
The subatomic
particles in a helium
atom.
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2-1 The Nature of Matter
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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2-1 The Nature of Matter
Elements and Isotopes
The number of protons in an atom of an element is
the element's atomic number.
Commonly found in living organisms:
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2-1 The Nature of Matter
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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2-1 The Nature of Matter
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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2-1 The Nature of Matter
Elements and Isotopes
Isotopes of Carbon
6 electrons
6 protons
8 neutrons
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2-1 The Nature of Matter
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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2-1 The Nature of Matter
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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2-1 The Nature of Matter
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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2-1 The Nature of Matter
Chemical Compounds
Chemical Formula
Water
Table Salt
Hydrochloric Acid
Glucose
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2-1 The Nature of Matter
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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2-1 The Nature of Matter
Chemical Bonds
The main types of chemical bonds are:
• ionic bonds
• covalent bonds
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2-1 The Nature of Matter
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
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known as ions.
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2-1 The Nature of Matter
Chemical Bonds
Sodium ion (Cl-)
Sodium atom (Na)
Sodium ion (Na+)
Sodium atom (Cl)
Protons
Electrons
+11
- 11
10
Protons
Electrons
+17
18
- 17
Charge
+10
Charge
-10
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2-1 The Nature of Matter
Chemical Bonds
Covalent Bonds
Sometimes electrons are shared by atoms instead
of being transferred.
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2-1 The Nature of Matter
Chemical Bonds
A covalent bond forms when electrons are shared
between atoms.
• single covalent bond
• double bond
• triple bond
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2-1 The Nature of Matter
Chemical Bonds
The structure that results when atoms are joined
together by covalent bonds is called a molecule.
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2-1 The Nature of Matter
Chemical Bonds
Van der Waals Forces
When molecules are close together, a slight
attraction can develop between the oppositely
charged regions of nearby molecules.
van der Waals forces
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2-1
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Continue to:
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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.
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