the octet rule in covalent bonding
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8.2. The Octet Rule in Covalent Bonding. The Octet Rule in Covalent Bonding What is the result of electron sharing in covalent bonds?. 8.2. The Octet Rule in Covalent Bonding. In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. - PowerPoint PPT PresentationTRANSCRIPT
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The Nature of Covalent Bonding
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8.2 The Octet Rule in Covalent Bonding
The Octet Rule in Covalent Bonding
What is the result of electron sharing in covalent bonds?
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The Nature of Covalent Bonding
>8.2 The Octet Rule in Covalent Bonding
In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.
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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.
8.2
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The Nature of Covalent Bonding
>8.2 Single Covalent Bonds
An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots.
A structural formula represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms.
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The Nature of Covalent Bonding
> Single Covalent Bonds
The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.
8.2
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The Nature of Covalent Bonding
>8.2 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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The Nature of Covalent Bonding
> Single Covalent Bonds
The hydrogen and oxygen atoms attain noble-gas configurations by sharing electrons.
8.2
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The Nature of Covalent Bonding
> Single Covalent Bonds
The ammonia molecule has one unshared pair of electrons.
8.2
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The Nature of Covalent Bonding
> Single Covalent Bonds
Methane has no unshared pairs of electrons.
8.2
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Section Assessment8.1
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Section Assessment
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Section Assessment
8.1
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Practice Problems
Section Assessment
Problem Solving 8.8 Solve Problem 8 with the help of an interactive guided tutorial.
for Conceptual Problem 8.1
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The Nature of Covalent Bonding
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8.2 Double and Triple Covalent Bonds
Double and Triple Covalent Bonds
How do atoms form double or triple covalent bonds?
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The Nature of Covalent Bonding
>8.2 Double and Triple Covalent Bonds
Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.
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The Nature of Covalent Bonding
>8.2 Double and Triple Covalent Bonds
A bond that involves two shared pairs of electrons is a double covalent bond. (ex: O2 has a double covalent bond between the two oxygen atoms)
A bond formed by sharing three pairs of electrons is a triple covalent bond. (ex. N2 has a triple covalent bond between the two nitrogen atoms)
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The Nature of Covalent Bonding
> Double and Triple Covalent Bonds
O2 molecule: Each oxygen atom has two unshared pair of electrons. N2 molecule: Each nitrogen has one pair of unshared electrons
Lewis dot structure of O2 and N2
8.2
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The Nature of Covalent Bonding
>8.2 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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The Nature of Covalent Bonding
> Double and Triple Covalent Bonds
Carbon dioxide is an example of a triatomic molecule.
8.2
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The Nature of Covalent Bonding
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8.2 Coordinate Covalent Bonds
Coordinate Covalent Bonds
How are coordinate covalent bonds different from other covalent bonds?
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The Nature of Covalent Bonding
>8.2 Coordinate Covalent Bonds
In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms.
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The Nature of Covalent Bonding
>8.2 Coordinate Covalent Bonds
A coordinate covalent bond is a covalent bond in which one atom contributes both bonding electrons.
In a structural formula, you can show coordinate covalent bonds as arrows that point from the atom donating the pair of electrons to the atom receiving them.
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Section Assessment8.2
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Section Assessment
8.2
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Section Assessment8.2
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The Nature of Covalent Bonding
> Coordinate Covalent Bonds
A polyatomic ion, such as NH4+, is a tightly
bound group of atoms that has a positive or negative charge and behaves as a unit. One of its bonds is a coordinate covalent bond.
Most plants need nitrogen that is already combined in a compound to grow.
8.2
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The Nature of Covalent Bonding
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Bonding in:NaCl ?HCl ? H2O ?
Bonding in ionic compounds containing polyatomic ions:Na2CO3 ?BaSO4 ? NH4Cl ?
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The Nature of Covalent Bonding
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Bond Dissociation Energies
Bond Dissociation Energies
How is the strength of a covalent bond related to its bond dissociation energy?
8.2
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The Nature of Covalent Bonding
> Bond Dissociation Energies
The energy required to break the bond between two covalently bonded atoms is known as the bond dissociation energy.
A large bond dissociation energy corresponds to a strong covalent bond.
8.2
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The octet rule does not allow us to understand bonding in ALL molecules.
Resonance is a concept used to explain some of the compounds that do not conform to the octet rule (Ex. Ozone O3)
Other theories? Molecular Orbital Theory
Other Theories of Bonding?
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The Nature of Covalent Bonding
> Resonance
Ozone in the upper atmosphere blocks harmful ultraviolet radiation from the sun. At lower elevations, it contributes to smog.
8.2
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The Nature of Covalent Bonding
> Resonance
The actual bonding of oxygen atoms in ozone is a hybrid, or mixture, of the extremes represented by the resonance forms.
8.2
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The Nature of Covalent Bonding
> Resonance
A resonance structure is a structure that occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion.
8.2
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The Nature of Covalent Bonding
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Exceptions to the Octet Rule
Exceptions to the Octet Rule
What are some exceptions to the rule?
The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number (ex. NO2) There are also molecules in which an atom has fewer (ex, BF3), or more (ex. SF6; PCl5), than a complete octet of valence electrons.
8.2
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Section Quiz
-or-Continue to: Launch:
Assess students’ understanding of the concepts in Section 8.2.
8.2 Section Quiz.
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1. In covalent bonding, atoms attain the configuration of noble gases by
a. losing electrons.
b. gaining electrons.
c. transferring electrons.
d. sharing electrons.
8.2 Section Quiz.
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8.2 Section Quiz
2. 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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3. 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
8.2 Section Quiz
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8.3VSEPR Theory
VSEPR Theory
How does VSEPR theory help predict the shapes of molecules?
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8.3VSEPR Theory
a. The hydrogens in a methane molecule are at the four corners of a geometric solid. All of the H—C—H angles are 109.5°, the tetrahedral angle. (See Models)
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8.3VSEPR Theory
a. The valence-shell electron-pair repulsion theory, or VSEPR theory, explains the three-dimensional shape of methane.
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8.3VSEPR Theory
According to VSEPR theory, the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.
HCl, Cl2 are linear diatomic molecules
CO2 is linear triatomic
H2O has a bent shape, NH3 has a pyramidal shape and CH4 has a tetrahedral shape.
Activity: Molecular Models Lab
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8.3VSEPR Theory
a. NH3 has a pyramidal shape and the measured H—N—H bond angle is about 107.
b. (See Models)
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8.3VSEPR Theory
a. H2O has a bent shape and the measured bond angle in water is about 105°. (See Models)