1. Unit 3 Lesson 3 Electrons and Chemical Bonding
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2. Bound to Change How do atoms join together?
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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3. What happens to atoms during chemical changes?
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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4. A Model Atom What do different atom models show?
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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5. What do different atom models show?
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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6. What do different atom models show?
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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7. What do different atom models show?
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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8. What do different atom models show?
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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9. What do different atom models show?
This model uses spheres to show the 3-D arrangement of atoms.

10. What are valence electrons?
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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11. 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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12. How does the periodic table show the number of valence electrons?

13. How does the periodic table show the number of valence electrons?
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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14. 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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15. 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.
When one atom loses an electron it becomes positively charged. That lost electron “jumps” or is transferred to another atom causing it to become negatively charged. The two atoms are now attracted to each other and bond, sharing the 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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16. When Atoms Combine Chemical Bond
1 molecule of Sodium Chloride (Table salt)