1. Chapter Eight Molecular Structure
The chemical bond is a strong attractive force that exists between certain atoms in a substance.
Ionic bond
The chemical bond
Covalent bond*
van der Waals forces
Intermolecular
forces*
hydrogen bonding
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2. 8-3 Intermolecular Forces
8-1 Ionic Bonds
8-2 Covalent Bonds
8-3 Intermolecular Forces
8-2.1 The Lewis Theory
8-2.2 The Valence-Shell Electron-Pair
Repulsion (VSEPR) Model
8-2.3 Valence Bond Theory
8-2.4 Hybrid Orbital Theory
8-2.5 Molecular Orbital Theory
The Polarity Of Molecules
Van Der Waals Forces
The Hydrogen Bond
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3. 8-2 Covalent Bonds
Covalent bond, is a chemical bond formed by the sharing of a pair of electrons between the two atoms.
There are several theories to explain the formation of covalent bond:
The Lewis Theory
The Valence-Shell Electron-Pair
Repulsion (VSEPR) Model
Valence Bond Theory
Hybrid Orbital Theory
Molecular Orbital Theory
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4. 8-2.1 The Lewis Theory Gilbert Newton Lewis (1875-1946)
was nominated for the Nobel Prize
in chemistry over 30 times, and still
today, many scientists believe he
well deserved it.
Lewis became the mentor to
290 Ph.D. recipients and 20
Nobel Prize winners.
He directed the experiments
that resulted in the discovery
of elements
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5. The octet rule, which says that atoms tend to lose, gain or share electrons when bonding to have eight electrons in their valence shells (outer electron shell).
(Elements of lowest atomic number tend to lose or gain electrons to give a single shell of two electrons, as in the noble gas Helium.)
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9. H : H
Electron-dot formula (also called a Lewis formula) is a formula that uses pairs of dots to represent covalent bonds, as well as dots to represent the electrons on individual atoms
F-F F2
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10. Multiple Bonds
Single bond: a covalent bond formed by the sharing of a single pair of electrons between two atoms
Double bond: a covalent bond formed by the sharing of two pairs of electrons between two atoms
Triple bond: a covalent bond formed by the sharing of three pairs of elections between two atoms
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12. Lone pair Bonding pair Bonding pair Bonding pair
Bonding Pairs and Lone Pairs
A bonding pair is an electron pair that is shared between two atoms.
A lone pair (or nonbonding pair) is an electron pair that is on one atom, it is not involved in bonding.
Lone pair
Bonding
pair
Bonding
pair
Bonding
pair
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13. + H Coordinate covalent bond
Coordinate covalent bond is formed when both electrons of the bond are donated by one atom + H
Coordinate
covalent bond
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15. 8-2.3 Valence Bond Theory 1. The Formation of a Covalent Bond
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16. 8-2. 3 Valence Bond Theory 1. The Formation of a Covalent Bond 84pm
84pm
Valence Bond Theory
1. The Formation of a Covalent Bond
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17. 2. The Central Themes of VB Theory
(1) Opposing Spins of the Electron Pair
As the exclusion principle prescribes,
the molecule formed by the overlapping
orbitals has a maximum capacity of two
electrons that must have opposite spins.
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18. (2) The Number of the Covalent Bond Saturation character
The number of bonds formed by a given atom
to equal the number of unpaired electrons in its
valence shell.
For example, nitrogen with the out configuration
2s22px12py12pz1, can share its 2p electrons with
three hydrogen atom to form three bonds, as in
NH3 (ammonia), but it cannot form NH5.
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19. (3) Maximum Overlap of Bonding Orbitals
Direction character
An orbital on one atom comes to occupy a
portion of the same region of space as an orbital
on the other. The two orbitals are said to overlap.
the greater the orbital overlap, the stronger
(more stable) the bond.
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20. To maximize overlap in HCl, half-filled H ls and +
To maximize overlap in HCl, half-filled H ls and
Cl 3p orbitals overlap along the long axis of the
3p orbital involved in bonding.
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21. 3. The classification of covalent bonds
Sigma Bond
A. Two kinds of bonds
Pi Bond
Sigma bond (σ) is formed by the overlap
of the end of one orbital with the end of the
other. It has a cylindrical shape symmetry
about the bond axis. Sigma bonds are
exemplified by s-s, s-px, and px-px overlaps.
(head to head)
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22. (2) A pi bond (л) is formed by the sidewise
overlap of two parallel p orbitals.
(side to side)
Pi bonds are exemplified by
py-py, and pz-pz overlaps.
a sidewise overlap will not give so
strong a bond as an along-the-axis
overlap of two p orbitals.
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23. The overlap of orbitals to form sigma bond s-s overlap px-px overlap
s-px overlap
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24. The overlap of orbitals to form л bond
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25. s-s overlap s-px overlap px-px overlap σ bond py-py overlap
pz-pz overlap
Л bond
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26. B．Coordinate Covalent Bonds
A coordinate covalent bond is a bond in which
both electrons of a shared pair come from one of
the two atoms involved in the bond.
H+ + :NH [ H NH3 ]+ ←
C O
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27. 4. Bond parameters bond length bond energy bond angle
The bond length is defined as the distance
between the nuclei of the atoms involved
in the bond.
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28. I-I
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29. Bond energy is determined by the energy required to break one
mole of bonds
in a gaseous
species.
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30. 2pz 2px 2py The bond angle is the angle formed by the
nuclei of two surrounding atoms with the
nucleus of the central
atom at the vertex.
2pz
2px
2py
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