1. Example: Oxygen – oxygen atoms; Hydrogen – hydrogen atoms
What is an element?
An element is a substance that is made up entirely of a single kind of atom.
Example: Oxygen – oxygen atoms; Hydrogen – hydrogen atoms
Inside the nucleus of an atom
Protons – + charge
Neutrons – neutral charge
Outside the nucleus of an atom
Electrons – (-) charge
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2. Atoms can form ions by gaining or losing electrons.
Section 4.10
Ions
Atoms can form ions by gaining or losing electrons.
Metals tend to lose one or more electrons to form positive ions called cations.
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3. Section 4.10
Ions
Nonmetals tend to gain one or more electrons to form negative ions called anions.
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4. Oxidation – loss of an electron Reduction – gain of an electron
Section 4.10
Ions
Oxidation – loss of an electron
Reduction – gain of an electron
Oil Rig – Oxidation is losing; Reduction is gaining
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5. A compound is made of atoms of different elements bonded together.
water (H2O)
carbon dioxide (CO2)

6. Na loses an electron to CI
Ionic bonds form between oppositely charged ions.
Sodium atom (Na)
Chlorine atom (CI)
Sodium ion (Na+)
Chloride ion (CI-)
Na loses an electron to CI
ionic bond
gained electron

7. multiple covalent bonds
A covalent bond forms when atoms share a pair of electrons.
multiple covalent bonds
diatomic molecules
covalent bonds
Oxygen atom (O)
Carbon atom (C)
Carbon dioxide (CO2 )

8. Ion Charges and the Periodic Table
Section 4.10
Ions
Ion Charges and the Periodic Table
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9. What is the difference between an atom and an ion?
A. An atom must lose protons to form an ion
B. An atom always has a neutral charge whereas an ion can have either charge.
C. An atom always has a positive charge whereas an ion can have either charge.
D. There is no difference.
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10. A. Two electrons; oxidation B. Two electrons; reduction
The element carbon has six electrons (or four valance electrons. How many electrons must it obtain to fill its valence shell and is this oxidation or reduction?
A. Two electrons; oxidation
B. Two electrons; reduction
C. Four electrons; oxidation
D. Four electrons; reduction
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11. Potassium (K) has one valence electron in its outer shell
Potassium (K) has one valence electron in its outer shell. What will the charge be for K if it forms a molecule with another atom (KCl) and will K be a cation or anion?
A. Anion; +1
B. Anion; -1
C. Cation; +1
D. Cation; -1
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