12.1 Types of Chemical Bonds

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Chapter 12

• 12.1 Types of Chemical Bonds
• 12.2 Electronegativity

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12.1 Types of Chemical Bonds

• Objectives
• To learn about ionic and covalent bonds and
  explain how they are formed.
• To learn about the polar covalent bond.

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Molecular Bonding and Structure play the central
role in determining the course of chemical
reactions, many of which are vital to our
survival.
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Structure plays a central role in our senses of
smell and taste.Substances have a particular
odor because they fit into the specially shaped
receptors in our nasal passages.
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12.1 Types of Chemical Bonds

• Bond force that holds groups of 2 or more atoms
  together and makes them function as a unit.
• Bond energy energy required to break the bond.
  This gives information about the strength of a
  bond.

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12.1 Types of Chemical Bonds

• Ionic bonding attraction between closely packed
  opposite charged ions.
• Metal Nonmetal Ionic Compound
• M X MX-
• Ionic compound metal reacts with a nonmetal

e-
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12.1 Types of Chemical Bonds

• Covalent bonds electrons are shared by nuclei

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12.1 Types of Chemical Bonds

• Polar covalent bonds electrons are unequally
  shared by nuclei. When 2 nonmetals react.

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12.2 Electronegativity

• Objectives To understand the nature of bonds and
  their relationship to electronegativity.
• Electronegativity relative ability of an atom in
  a molecule to attract shared electrons to itself.
• Chemists determine this by measuring the polarity
  of the bonds between various atoms.

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Polarity of a bond depends on the
difference between the electronegativity values
of the atoms forming the bond. If this
difference is small relatively nonpolar If this
difference is large more polar gt2 IONIC
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Table 12.1
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Covalent bond between 2 identical atoms.
Polar covalent bonds
Ionic Bond with no electron sharing
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Lets Practice

• Which is the more polar pair?
• 1) H-S or H-F

H-F
O-S
2) O-S or O-F
C-Cl
3) C-S or C-Cl
Homework Self-check Exercise 12.1 8-12 p. 394-395
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12.3 Bond Polarity and Dipole Moment

• Objective To understand bond polarity and how it
  is related to molecular polarity

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12.3 Bond Polarity and Dipole Moments
Dipole moment a molecule that has a center of
positive charge and a center of negative
charge. Dipole character is often represented by
an arrow.
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12.3 Bond Polarity and Dipole Moment
The fact that water is a polar allows water to
attract both positive and negative ions. This
allows many things to dissolve in water.
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12.4 Stable Electron Configurations and Charges
on Ions

• Objectives To learn about stable electron
  configurations.
• To learn to predict the formulas of ionic
  compounds.

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Table 12.2
When a metal reacts with a nonmetal the metal
loses electrons and the nonmetal Gains these
electrons.
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12.4 Stable Electron Configurations and Charges
on Ions

• In almost all stable chemical compounds
• Of the representative elements, all of the atoms
  have achieved a noble gas electron configuration.

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Table 12.3
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12.4 Stable Electron Configurations and Charges
on Ions

• So what do we need to know this for
• Ca Ar4s2
• O He2s22p4.
• Calculate the electronegativity
• Oxygen is 3.5, Ca is 1.0 Difference is 2.5
• So how many electrons are transferred?

CaO is the empirical formula
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12.5 Ionic Bonding and Structures of Ionic
Compounds

• Objectives To learn about ionic structures
• To understand factors governing ionic size.

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Anion is always larger than the parent atom.
Cation is always smaller than the parent atom
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WHY?
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A note on polyatomics

• Polyatomic ions
• NH4 and NO3- are held together by covalent
  bonds.

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12.6 Lewis Structures

• Objective To learn to write Lewis structures

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12.6 Lewis Structures

• Bonding involves just the valence electrons.
• Lewis structure representation of a molecule
  that shows how the valence electrons are arranged
  among the atoms in the molecule.
• Name after G.N. Lewis who used it as a tool to
  teach Chemistry students.

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12.6 Lewis Structures

• Example
• K Br- Ionic Bonds
• Covalent Bonds
• Duet rule for Hydrogen HH
• Octet rule surrounded by 8 electrons FF

..
..
Bonding pair
..
..
..
..
Lone pairs or Unshared pairs
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12.6 Lewis Structures

• Example Write the Lewis structures of the
  following molecules. CCl4 PH3

..
..
Cl ClCCl Cl
STEPS 1) Get the sum of the valence electrons
from all of the atoms. 2) Use one
pair of electrons to form a bond between each
pair of bound atoms. 3)
Arrange the remaining electrons to satisfy the
octet rule or duet rule
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12.7Lewis Structures of Molecules w/Multiple Bonds
Objective To learn how to write Lewis structures
for molecules with multiple bonds.
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12.7Lewis Structures of Molecules w/Multiple Bonds

• Example Write the Lewis structures of the
  following molecules. CO2
  

4 6 6 16 valence electrons
..
..
..
..
OCO
Single Bond shares 1 pair of electrons
But this is not correct because ?
..
..
OCO
DOUBLE BOND- 2 PAIRS of e-
BUT
..
..
Triple Bond-3 e- pairs
RESONANCE more than one Lewis structure can be
drawn for the molecule.
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12.7Lewis Structures of Molecules w/Multiple Bonds
Some exceptions to the Octet Rule Boron tends to
form compounds in which the boron has fewer Than
8 electrons around it.
F
VERY REACTIVE w/ NH3 and H2O
H
F
B
H-N-B-F
F
F
F
H
Another exception
..
..
HOWEVER, Oxygen is paramagnetic Which suggests
an unpaired electrons.
OO
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12.8 Molecular Structure

• Molecular or geometric structure 3-Dimensional
  arrangement of the atom in a molecule.

BENT or V-shaped Bond angle about 105o
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12.8 Molecular Structure

• Molecular or geometric structure 3-Dimensional
  arrangement of the atom in a molecule.

Linear structure Bond angle 180o
F
120o
Trigonal planar
B
F
F
Tetrahedral structure
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12.9 Molecular Structure The VSEPR Model

• Objective To learn to predict molecular geometry
  from the number of electron pairs.

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12.9 Molecular Structure The VSEPR Model

• VSEPR valence shell electron pair repulsion
  model.
• -is that the structure around a given atom is
  determined by minimizing repulsions between
  electron pairs.
• -bonding and nonbonding electron pairs are
  positioned as far apart as possible.

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Predicting the Molecular Structureusing the
VSEPR model

• Step 1 Draw the Lewis structure for the
  molecule.
• Step 2 Count the electron pairs and arrange them
  in the way that minimizes repulsions.
• (as far apart as possible)
• Step 3 Determine the positions of the atoms from
  the way the electron pairs are shared.
• Step 4 Determine the name of the molecular
  structure from the positions of the atoms.

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Example

• NH3

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Table 12.4
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12.10Molecular Structure with Double Bonds

• Objective To learn to apply the VSEPR model to
  molecules with double bonds.

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12.10Molecular Structure with Double Bonds

• When using the VSEPR model to predict the
  molecular geometry of a molecule, a double bond
  is counted the same as a single electron pair.
• SOOOO
• apply the same rules as for single bonds.

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12.10Molecular Structure with Double Bonds

• CO2-planar
• NO3-trigonal planar

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