Unit 3 Lesson 3 Electrons and Chemical Bonding
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Unit 3 Lesson 3 Electrons and Chemical Bonding
Bound to Change
How do atoms join together?
•  A huge variety of substances are possible because
atoms join together by forming chemical bonds.
•  A chemical bond is an interaction that holds
atoms or ions together.
•  A group of atoms that are held together by
chemical bonds is called a molecule.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
What happens to atoms during
chemical changes?
•  Chemical changes change the identity of
substances.
•  Chemical changes do not create or destroy atoms.
In a chemical change, atoms are rearranged to
make new substances with different properties.
•  In order for atoms to be rearranged, chemical
bonds have to be formed or broken.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
A Model Atom
What do different atom models show?
•  The electron cloud model of an atom shows how
electrons are found in a region around the
nucleus.
•  This model helps to show the general locations of
the different parts of the atom.
•  However, it does not show the number of
electrons.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
What do different atom models show?
•  Where are the nucleus and the electrons in the
electron cloud model of a lithium atom?
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Unit 3 Lesson 3 Electrons and Chemical Bonding
What do different atom models show?
•  The Bohr model of an atom shows the number of
electrons in an atom.
•  The electrons are shown as dots placed in rings
around the nucleus, with each ring representing
an energy level.
•  Showing the electrons in energy levels helps
predict how and why atoms form chemical bonds.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
What do different atom models show?
•  How are electrons distributed in the Bohr model of
an oxygen atom?
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Unit 3 Lesson 3 Electrons and Chemical Bonding
What do different atom models show?
•  In the space-filling model of a molecule, atoms
are represented as solid spheres.
•  The spheres do not show the parts that make up
the atoms.
•  However, this model clearly shows how the atoms
are connected to each other.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
What are valence electrons?
•  Bohr models show electrons in energy levels, each
of which can hold a specific number of electrons.
•  The energy level furthest from the nucleus is
called the outermost energy level.
•  Electrons found in the outermost energy level of
an atom are called valence electrons.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
Fill It Up!
How does the periodic table show the
number of valence electrons?
•  Elements in the same group, or vertical column,
have the same number of valence electrons.
•  You can use the group number to find the number
of valence electrons in Groups 1, 2, and 13–18.
•  There is no simple rule to find the number of
valence electrons in Groups 3–12.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
How does the periodic table show the
number of valence electrons?
•  Determine the number of valence electrons in
atoms of carbon (C), nitrogen (N), and fluorine
(F).
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Unit 3 Lesson 3 Electrons and Chemical Bonding
Why do atoms form bonds?
•  An atom tends to form bonds if its outermost
energy level is not full.
•  Atoms that have fewer than eight valence
electrons, except for helium, do not have a full
outermost energy level.
•  These atoms gain, lose, or share valence electrons
to form bonds.
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Unit 3 Lesson 3 Electrons and Chemical Bonding
Why do atoms form bonds?
•  Forming bonds allows atoms to fill their outermost
energy level.
•  An ion is a charged particle that forms when an
atom loses or gains an electron.
•  The ions formed by chlorine and sodium both have
eight valence electrons. Bonds hold the negative
and positive ions together, producing sodium
chloride.
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