Students, Describe ionic, metallic and covalent bonds. Slide
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8.2
The Nature of Covalent Bonding
The colors in this map
indicate the concentrations
of ozone in various parts of
Earth’s atmosphere.
Oxygen atoms can join in
pairs to form the oxygen
you breathe and can also
join in groups of three
oxygen atoms to form
ozone.
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5. Describe how electrons are shared to form covalent bonds using the octet rule and identify exceptions to the octet rule. 6. Demonstrate how Lewis structures (electron dot structures) represent shared electrons.
7. Draw Lewis structures for molecules and polyatomic ions.
8. Describe how atoms form double or triple covalent bonds.
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• Ionic Bonds: – Electron transfer from metal to non‐metal ions
– Opposites attract
• Metallic Bonds
– Closely packed cations in a sea of valence electrons
• Covalent Bonds:
– The sharing of electrons
– The octet rule is the driving force behind how they bond
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• Single covalent bonds:
– 2 atoms share one pair of e‐’s to achieve a stable electron configuration
– Examples: Draw the Lewis structure for H2
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8.2
The Nature of
Covalent Bonding
>
Single Covalent Bonds
Two atoms held together by sharing a pair of
electrons are joined by a single covalent bond.
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8.2
The Nature of
Covalent Bonding
>
Single Covalent Bonds
The halogens form single covalent bonds in their
diatomic molecules. Fluorine is one example.
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8.2
The Nature of
Covalent Bonding
>
Single Covalent Bonds
A pair of valence electrons that is not shared
between atoms is called an unshared pair, also
known as a lone pair or a nonbonding pair.
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8.2
The Nature of
Covalent Bonding
>
Single Covalent Bonds
The hydrogen and oxygen atoms attain noblegas configurations by sharing electrons.
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8.2
The Nature of
Covalent Bonding
>
Single Covalent Bonds
The ammonia molecule has one unshared pair
of electrons.
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8.2
The Nature of
Covalent Bonding
>
Single Covalent Bonds
Methane has no unshared pairs of electrons.
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• Double and triple covalent bonds – atoms share two or three pairs of electrons to attain a noble gas configuration
• Example: Sulfur dioxide: SO2
– Follow the steps to draw a Lewis structure, you will need a double covalent bond. 1. How many valence e‐’s? 18 e‐
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2. Place one pair of electrons in each bond
18 e‐
4 e‐ = 14 e‐
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3. Complete octets of atoms bonded to central atom
14 e‐
12e‐ = 2 e‐ left
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4. Place any addition e‐ on the central atom in pairs 14 e‐ ‐ 12e‐ = 2 e‐ left
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5. If the central atom still has less than an octet, form multiple bonds so that each atom has an octet
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• Triple covalent bond example N2
1. How many valence e‐?
• 10 e‐
2. Place electron pair in bond
• 8 e‐ left
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3. Complete octets
• 8 e‐ left
5. Form multiple bonds so that each atom has an octet
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8.2
The Nature of
Covalent Bonding
>
Double and Triple Covalent Bonds
Carbon dioxide gas is soluble in water and is
used to carbonate many beverages. A carbon
dioxide molecule has two carbon-oxygen double
bonds.
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8.2
The Nature of
Covalent Bonding
>
Double and Triple Covalent Bonds
Carbon dioxide is an example of a triatomic
molecule.
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• Coordinate covalent bonds
– one atom contributes both bonding electrons
– once formed they act like other covalent bonds
– example: CO
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• Polyatomic ions
– A group of two or more covalently bonded atoms (polyatomic) that behave as a unit and carry a charge (ion)
– Most have a negative charge
– One polyatomic ion with a positive charge = ammonium ion: NH4+ Slide
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• Drawing Lewis structures for polyatomic ions
– Remember to add or subtract e‐’s in the first step to represent the gain or loss of electrons
• for negative ions: add e‐
• for positive ions: subtract e‐
– Write the final structure in brackets with the charge outside the bracket
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• Draw a Lewis structure for the polyatomic ion sulfate (SO42‐)
1. Count all valence electrons
•
30e‐ + 2e‐ = 32 e‐
2. Place a pair of electrons in each bond
3. Complete octets of atoms bonded to the central atom
4. Write the structure in brackets with the charge outside
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8.2 Section Quiz.
In covalent bonding, atoms attain the configuration of noble gases by
A. losing electrons.
B. gaining electrons.
C. transferring electrons.
D. sharing electrons.
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8.2 Section Quiz
Electron dot diagrams are superior to molecular formulas in that they A. show which electrons are shared.
B. indicate the number of each kind of atom in the molecule.
C. show the arrangement of atoms in the molecule.
D. are easier to write or draw.
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8.2 Section Quiz
Which of the following molecules would contain a bond formed when atoms share three pairs of electrons?
A. Se2
B. As2
C. Br2
D. Te2
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• WS: Practice problems
• Read 226‐229
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