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Bonding
Chapter
Chemistry I Honors
Types of Chemical Bonds
Types of Bonds
✦
✦
Ionic
✦ Electrons are transferred
✦ Metals react with nonmetals
✦ Ions paired have lower energy (greater stability) than separated
ions
Covalent
✦ Electrons are shared by nuclei
✦ Pure covalent (nonpolar covalent) - electrons are shared evenly
✦ Polar covalent - electrons shared unequally
✦
Atoms end up with fractional charges (ς+ and ς-)
Electronegativity
Electronegativity
✦
✦
✦
Electronegativity is the ability of an atom in a molecule to attract
shared electrons to itself.
Trends
✦ increases across a period
✦ decreases down a group (family)
Greater electronegativity difference means less covalent and more
ionic character.
Electron Configuration and Physical Properties
Electronegativity
Electronegativity
Electronegativity
Sample Problem A
✦
In each case, which bond is more polar?
✦ B⎯Cl or C⎯Cl
✦ P⎯F or P⎯Cl
Covalent Bond Energies and Chemical Reactions
Bond Energies (Covalent)
ΔH = ∑ ( bond enthalpies of bonds broken ) − ∑ ( bond enthalpies of bonds formed )
Table 8.4 (p.351)
Covalent Bond Energies and Chemical Reactions
Bond Energies (Covalent)
Sample Problem B
✦
Estimate the ΔH for the following reaction
C2 H 6 ( g ) + O2 ( g ) ⎯⎯
→ 2CO2 ( g ) + 3H 2O ( g )
7
2
Covalent Bond Energies and Chemical Reactions
Bond Enthalpy and Bond Length
✦
As the number of bonds between two atoms increases, the bond
grows shorter and stronger.
Lewis Structures
Drawing Lewis Structures
1.Add up the total number of valence electrons from all atoms.
2.Use a pair of electrons to form a bond between each pair of bonded
atoms.
3.Arrange the remaining atoms to satisfy the duet rule for hydrogen
and the octet rule for 2nd row elements.
Lewis Structures
Drawing Lewis Structures
Sample Problem C
✦
Draw the following Lewis Structures
✦ PCl3
✦ CH2Cl2
✦ HCN
✦ NO+1
Lewis Structures
AP Exam Sample
Sample Problem D
Answer the following questions using principles of chemical bonding
and molecular structure.
a.Consider the carbon dioxide molecule, CO2, and the carbonate ion,
2CO3 .
i. Draw the complete Lewis electron-dot structures for each
species.
ii.Account for the fact that the carbon-oxygen bond length in
2CO3 is greater than the carbon-oxygen bond length in CO2.
Lewis Structures
AP Exam Sample
Sample Problem D
Answer the following questions using principles of chemical bonding
and molecular structure.
b.Consider the molecules CF4 and SF4.
i. Draw the complete Lewis electron-dot structures for each
molecule.
ii.In terms of molecular geometry, account for the fact that the
CF4 molecule is nonpolar, whereas the SF4 molecule is polar.
Lewis Structures
Resonance
✦
✦
When more than one valid Lewis structure can be written for a
particular molecule
Actual structure is an average of the depicted resonance structures
Lewis Structures
Resonance
Sample Problem E
✦
Draw the possible Lewis structures for the following:
✦ NO3-1
Covalent Bonding: Orbitals
Hybridization
✦
✦
The mixing of two or more atomic orbitals of similar energies on the
same atom to produce new orbitals of equal energies
Hybrid orbitals - equal energy produced by the combination of two
or more orbitals on the same atom
Covalent Bonding: Orbital
Hybridization
Sample Problem F
✦
Indicate the hybridization by the central atom in the following:
✦ NH2-1
✦ SF4
Molecular Structure: The VSEPR Model
VSEPR
✦
✦
✦
Structure around a given atom is determined by minimizing
electron-pair repulsion.
Non-bonding and bonding electron pairs will be as far apart as
possible
Multiple bonds count as one effective electron pair
Molecular Structure: The VSEPR Model
Effect of Unshared Electron Pairs
✦
✦
Lone pairs require more room than bonding pairs and tend to
compress the angles between bonding pairs.
Lone pairs do not cause distortion when bond angles are 120° or
greater
Molecular Structure: The VSEPR Model
VSEPR Theory
Sample Problem G
✦
Use VSEPR to predict the molecular geometry of the following:
✦ SF4
✦ IF5
Molecular Structure: The VSEPR Model
Paramagnetic vs. Diamagnetic
✦
✦
Paramagnetic elements have non-spin paired electrons in their
electron cloud.
Diamagnetic elements have all electrons spin paired in their electron
cloud.
Molecular Structure: The VSEPR Model
AP Exam Practice
Sample Problem H
Answer the following questions about the element selenium, Se
(atomic number 34).
a.Samples of natural selenium contains six stable isotopes. In terms
of atomic structure, explain what these isotopes have in common,
and how they differ.
b.Write the complete electron configuration for a selenium atom in
the ground state. Indicate the number of unpaired electrons in the
ground-state atom, and explain your reasoning.
Molecular Structure: The VSEPR Model
AP Exam Practice
Sample Problem H
Answer the following questions about the element selenium, Se
(atomic number 34).
c.In terms of atomic structure, explain why the first ionization
energy of selenium is
i. less than that of bromine (atomic number 35), and
ii.greater than that of tellurium (atomic number 52).
d.Selenium reacts with fluorine to form SeF4. Draw the complete
Lewis electron dot structure for SeF4 and sketch the molecular
structure. Indicate whether the molecule is polar or nonpolar, and
justify your answer.
Covalent Bonding: Orbital
AP Exam Practice
Sample Problem I
GeCl4
SeCl4
ICl4
+
ICl4
The species represented above all have the same number of chlorine
atoms attached to the central atom.
a.Draw the Lewis structure of each of the four species. Show all
valence electrons in your structures.
Covalent Bonding: Orbital
AP Exam Practice
Sample Problem I
GeCl4
SeCl4
ICl4
+
ICl4
The species represented above all have the same number of chlorine
atoms attached to the central atom.
b.On the basis of the Lewis structures drawn in part (a), answer the
following questions about the particular species indicated.
i. What is the Cl-Ge-Cl bond angle in GeCl4?
ii.Is SeCl4 polar? Explain.
iii.What is the hybridization of the I atom in ICl4 ?
+
iv.What is the geometric shape formed by the atoms in ICl4 ?