Download Drawing Electron

Chapter 10 Lecture
Basic Chemistry
Fourth Edition
Chapter 10 Properties of Solids
and Liquids
10.1 Electron-Dot Formulas
Learning Goal Draw the electron-dot
formulas for molecular compounds or
polyatomic ions with multiple bonds
and show resonance structures.
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Chapter 10 Readiness
Core Chemistry Skills
• Using Significant Figures in Calculations (2.4)
• Using Conversion Factors (2.7)
• Classifying Matter (3.1)
• Identifying Physical and Chemical Changes (3.2)
• Using Energy Units (3.4)
• Using the Heat Equation (3.4)
• Drawing Electron-Dot Symbols (5.6)
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Electron-Dot Symbols
Electron-dot symbols show
• one to four valence electrons as single dots on
the sides of an atomic symbol
• five to eight valence electrons with one or
more pairs of dots on the sides of an atomic
symbol
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Electron-Dot Symbols of Some
Representative Elements
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Electron-Dot Formulas
Electron-dot formulas show
• the sequence of bonded atoms in a molecule or
polyatomic ion
• the bonding pairs of electrons shared
between atoms
• the nonbonding or unshared (lone pairs) of
electrons
• the central atom bonded to other atoms
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Lone Pairs and Bonding Pairs
The electron-dot formula for
H
O
H
H2O contains:
• 8 valence electrons (6 from O plus 1 from each
hydrogen atom)
• O as the central atom
• two bonding pairs (between the H and O
atoms) and two lone pairs (on the O atom)
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Drawing Electron-Dot Formulas
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Writing Electron-Dot Formulas
Draw the electron-dot formula for PCl3,
phosphorus trichloride, used to prepare
insecticides and flame retardants.
Step 1 Determine the arrangement of atoms.
The central atom is P; there is only one
P atom.
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Writing Electron-Dot Formulas
Draw the electron-dot formula for PCl3.
Step 2 Determine the total number of valence
electrons.
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Writing Electron-Dot Formulas
Draw the electron-dot formula for PCl3.
Step 3 Attach each bonded atom to the
central atom with a pair of electrons.
Bonding electrons can also be
represented by a line.
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Writing Electron-Dot Formulas
Draw the electron-dot formula for PCl3.
Step 4 Place the remaining electrons using
single or multiple bonds to complete
the octets.
© 2014 Pearson Education, Inc.
Writing Electron-Dot Formulas
Draw the electron-dot formula for PCl3.
Step 4 Place the remaining electrons using
single or multiple bonds to complete
the octets.
Use the remaining 20 e− as lone pairs on
P and Cl atoms to complete octets.
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Learning Check
Write the electron-dot formula for ClO3−.
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Solution
Draw the electron-dot formula for ClO3−.
Step 1 Determine the arrangement of atoms.
The central atom is Cl; there is only one
Cl atom.
O
O Cl O
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-
−
Solution
Draw the electron-dot formula for ClO3− .
Step 2 Determine the total number of valence
electrons.
Element
Cl
O
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Group
7A (17)
6A (16)
Atoms
1 Cl
3O
Valence
Electrons
× 7 e−
× 6 e−
Total
= 7−
= 18 e−
Solution
Draw the electron-dot formula for ClO3−.
Step 3 Attach each bonded atom to the
central atom with a pair of electrons.
Bonding electrons can also be
represented by a line.
O
O Cl O
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-−
O
O Cl O
-−
Solution
Draw the electron-dot formula for ClO3− .
Step 4 Place the remaining electrons using
single or multiple bonds to complete
the octets.
© 2014 Pearson Education, Inc.
Solution
Draw the electron-dot formula for ClO3−.
Step 4 Place the remaining electrons using
single or multiple bonds to complete
the octets.
Use the remaining 20 e− as lone pairs on
Cl and O atoms to complete octets.
O
O Cl O
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-
−
O
O Cl O
-
−
Multiple Bonds
Multiple bonds form when there are not enough
valence electrons to complete octets.
• In a single bond, one pair of electrons is
shared.
• In a double bond, two pairs of electrons are
shared.
• In a triple bond, three pairs of electrons are
shared.
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Multiple Bonds, CO2
In carbon dioxide, CO2, octets are achieved by
sharing two pairs of electrons between atoms;
this is called a double bond.
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Multiple Bonds, N2
In nitrogen, N2, octets are achieved by sharing
three pairs of electrons between atoms; this is
called a triple bond.
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Resonance Structures
Resonance structures
• may be written for molecules or polyatomic
ions with multiple bonds
• consist of two or more electron-dot formulas
for the same arrangement of atoms
• are shown with a double-headed arrow
• are written by changing the location of a
double bond
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Resonance Structures, O3
Molecules that contain multiple bonds may
contain more than one electron-dot formula.
Ozone, O3 is a
component in the
stratosphere that
protects us from
the ultraviolet rays
of the Sun.
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Resonance Structures, O3
The electron-dot formula for O3 contains
• 18 valence electrons
• 3 bonding pairs
• 5 lone pairs
It is possible to draw two electron-dot structures
or resonance structures for O3.
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Learning Check
Carbonate has three resonance structures. If the
following is one, what are the other two?
-
2
2−
O
O
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C
O
Solution
Carbonate has three resonance structures. If the
following is one, what are the other two?
The double bond can also exist between the other
two oxygen atoms and the central carbon atom.
-
2
O
O
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C
O
-
2
O
O
C
O
-
2
O
O
C
O
Learning Check
Draw the two resonance structures for SO2.
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Solution
Draw the two resonance structures for SO2.
Step 1 Determine the arrangement of atoms.
The central atom is S, because there is
only one S atom in the formula.
S
O
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O
Solution
Draw the two resonance structures for SO2.
Step 2 Determine the total number of valence
electrons.
Element
S
O
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Group
6A (16)
6A (16)
Atoms
1S
2O
Valence
Electrons
× 6 e−
× 6 e−
Total
= 6e−
= 12e−
Solution
Draw the two resonance structures for SO2.
Step 3 Attach each bonded atom to the
central atom with a pair of electrons.
S
O
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O
Solution
Draw the two resonance structures for SO2.
Step 4 Place the remaining electrons using
single or multiple bonds to complete
the octets.
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Solution
Draw the two resonance structures for SO2.
Step 4 Place the remaining electrons using
single or multiple bonds to complete
the octets.
Use the remaining 14 e− as lone pairs on
S and O atoms. To complete the octet on
S, make a double bond.
O
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S
O
O
S
O
Exceptions to the Octet Rule
Exceptions to the octet rule include:
• hydrogen, H, only gets a single bond
• boron, B, has only 3 electrons around it to
form bonds
• compounds of P, S, Cl, Br, and I can have
expanded octets with 10, 12, or even
14 valence electrons around them
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Using Valence Electrons to Draw ElectronDot Formulas
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