Resonance Structures

Resonance Structures
Resonance structures are
 two or more electron-dot formulas for the same
arrangement of atoms.
 related by a double-headed arrow ( ).
 written by changing the location of a double bond
between the central atom and a different attached atom.
Writing Resonance Structures for SO2
Learning Check
FNO2, a rocket propellant, has two resonance structures. One is
shown below. What is the other resonance structure?
Solution
FNO2, a rocket propellant, has two resonance structures. One is
shown below. What is the other resonance structure?
Names of Covalent Compounds
When naming a covalent compound,
 the first nonmetal in the formula is named by its element
name, and
 the second nonmetal is named using the first syllable of its
element name, followed by ide.
Prefixes are used
 to indicate the number of atoms present for each element in
the compound, and
 because two nonmetals can form two or more different
compounds
Prefixes Used in Naming Covalent
Compounds
Some Covalent Compounds
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Chapter 5, Section 1
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Guide to Naming Covalent
Compounds with Two Nonmetals
Naming Covalent Compounds, SO2
Analyze the Problem.
Symbols of
Elements
Name
Subscripts
S
O
sulfur
oxygen
1
2
Prefix
(none) understood
di
Step 1 Name the first nonmetal by its element
name. In SO2, the first nonmetal (S) is sulfur.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
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Naming Covalent Compounds, SO2
Step 2 Name the second nonmetal by using the first
syllable of its name followed by ide. The
second nonmetal (O) is named oxide.
Step 3 Add prefixes to indicate the number of
atoms (subscripts). Because there is
one sulfur atom, no prefix is needed. The
subscript two for the oxygen atoms is written as
the prefix di .
The name of SO2 is sulfur dioxide.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
10
Learning Check
Name the covalent compound P2O5.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
11
Solution
Name the covalent compound P2O5.
Analyze the Problem.
Symbols of Elements
P
O
Name
Subscripts
Prefix
phosphorus
oxygen
2
5
di
penta
Step 1 Name the first nonmetal by its element
name. In P2O5, the first nonmetal (P) is
phosphorus.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
12
Solution
Step 2 Name the second nonmetal by using the first
syllable of its name followed by ide. The
second nonmetal (O) is named oxide.
Step 3 Add prefixes to indicate the number of
atoms (subscripts). The subscript for the two
P atoms is di; the subscript for the five oxygen
atoms is penta.
The name of P2O5 is phosphorus pentoxide.
When the vowels o and o, or a and o appear
together (pentaoxide), the first vowel is omitted.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
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Learning Check
Select the correct name for each compound.
1. SiCl4
A. silicon chloride
B. tetrasilicon chloride
C. silicon tetrachloride
#2
Name Cl2O7
A. dichlorine heptoxide
B. dichlorine oxide
C. chlorine heptoxide
Writing Formulas of Covalent Compounds
Write the formula for sulfur hexafluoride.
Analyze the Problem.
Name
sulfur
hexafluoride
Symbols of Elements
Subscripts
S
F
1
6 (from hexa)
Step 1 Write the symbols in order of the
elements in the name.
SF
Step 2 Write any prefixes as subscripts.
Prefix hexa = 6 Formula: SF6
Learning Check
Write the correct formula for dinitrogen trioxide.
Learning Check
Name each of the following compounds.
1. Ca3(PO4)2
2. FeBr3
3. SCl2
4. Cl2O
Solution
Name each of the following compounds.
1. Ca3(PO4)2
Ca2+, PO43−
calcium phosphate
2. FeBr3
Fe3+, Br −
iron(III) bromide
3. SCl2
1 S, 2 Cl
sulfur dichloride
4. Cl2O
2 Cl, 1 O
dichlorine oxide
Learning Check
Write the formulas for the following compounds.
1. calcium nitrate
2. boron trifluoride
3. aluminum carbonate
4. dinitrogen tetroxide
5. copper(I) phosphate
Solution
Write the formulas for the following compounds.
1. calcium nitrate
Ca2+, NO3−
Ca(NO3)2
2. boron trifluoride
1 B, 3 F
BF3
3. aluminum carbonate
Al3+, CO32−
Al2(CO3) 3
4. dinitrogen tetroxide
2 N, 4 O
N2O4
5. copper(I) phosphate
Cu+, PO43−
Cu3PO4
Electronegativity
Electronegativity
 is a measure of an atom’s ability to attract bonding
electrons.
 increases from left to right, going across a period on
the periodic table.
 decreases going down a group on the periodic table.
 is high for the nonmetals, with fluorine as the highest.
 is low for the metals and transition metals.
Bonding and Electronegativity
The difference in the electronegativity of two atoms can
be used to predict the type of bond that forms.
Bonds are classified as:
 nonpolar covalent
 polar covalent
 ionic
Some Electronegativity Values
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Chapter 5, Section 1
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Nonpolar Covalent Bonds
A nonpolar covalent bond
 occurs between nonmetals.
 has an equal or almost equal sharing of electrons.
 has almost no electronegativity difference (0.0 to 0.4).
Examples:
Atoms
Electronegativity
Difference
Type of Bond
Polar Covalent Bonds
A polar covalent bond
 occurs between nonmetal atoms that do not share
electrons equally.
 has a moderate electronegativity difference
(0.5 to 1.7).
Examples:
Atoms
Electronegativity
Type of Bond
Difference
Ionic Bonds
An ionic bond
 occurs between metal and nonmetal ions.
 is a result of electron transfer.
 has a large electronegativity difference (1.8 or more).
Examples:
Atoms
Electronegativity
Type of Bond
Difference
Electronegativity and Bond Types
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
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Predicting Bond Types
Learning Check
Use the electronegativity difference to identify the type of
bond between the following atoms as nonpolar covalent
(NP), polar covalent (P), or ionic (I).
A. K–N
2.2
B. N–O
0.5
C. Cl–Cl
0.0
D. B–Cl
1.0
Break Time!!!
Valence-Shell Electron-Pair Repulsion Theory
(VSEPR)
In the valence-shell electron-pair repulsion (VSEPR)
theory, the electron groups around a central atom
 are arranged as far apart from each other as possible.
 have the least amount of electron-electron repulsion.
 are used to predict the molecular shape.
Shapes of Molecules
The three-dimensional shape of a molecule can be
predicted by
 the number of bonding groups and lone-pair electrons
around the central atom
 VSEPR theory (valence-shell-electron-pair repulsion).
Two Electron Groups
In a molecule of BeCl2,
 there are two electron groups bonded to the central atom,
Be (Be is an exception to the octet rule).
 to minimize repulsion, the arrangement of two electron
groups is 180, or opposite each other.
 the shape of the molecule is linear.
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Chapter 5, Section 1
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Three Electron Groups
In a molecule of BF3,
 three electron groups are bonded to the central atom B (B
is an exception to the octet rule).
 repulsion is minimized with 3 electron groups at angles of
120.
 the shape is trigonal planar.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
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Three Electron Groups with a Lone Pair
In a molecule of SO2,
 S has 3 electron groups; 2 electron groups bonded to O
atoms and one lone pair.
 repulsion is minimized with the electron groups at angles
of 120, a trigonal planar arrangement.
 the shape is determined by the two O atoms bonded to S,
giving SO2 a bent (~120) shape.
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Chapter 5, Section 1
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Four Electron Groups
In a molecule of CH4,
 there are four electron groups around C.
 repulsion is minimized by placing four electron groups at
angles of 109, which is a tetrahedral arrangement.
 the four bonded atoms form a tetrahedral shape.
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Chapter 5, Section 1
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Four Electron Groups with a Lone Pair
In a molecule of NH3,
 three electron groups bond to H atoms, and the fourth one
is a lone (nonbonding) pair.
 repulsion is minimized with 4 electron groups in a
tetrahedral arrangement.
 the three bonded atoms form a pyramidal (~109) shape.
© 2013 Pearson Education, Inc.
Chapter 5, Section 1
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Four Electron Groups with Two Lone Pairs
In a molecule of H2O,
 two electron groups are bonded to H atoms and two are
lone pairs (4 electron groups).
 four electron groups minimize repulsion in a tetrahedral
arrangement.
 the shape with two bonded atoms is bent (~109).
Molecular Shapes for 2 and 3 Bonded
Atoms
Molecular Shapes for 4 Bonded Atoms
Guide to Predicting Molecular Shape
(VSEPR Theory)
Predicting the Molecular Shape of H2Se
Step 1 Draw the electron-dot formula. In the electrondot formula for H2Se, there are four electron
groups, including two lone pairs of electrons
around Se.
Predicting the Molecular Shape of H2Se
Step 2 Arrange the electron groups around the central
atom to minimize repulsion. The four electron
groups around Se would have a tetrahedral
arrangement.
Step 3 Use the atoms bonded to the central atom to
determine the molecular shape. Two bonded
atoms give H2Se a bent shape with a bond angle
of ~109.
Learning Check
What is the shape of a molecule of NF3?
Solution
What is the shape of a molecule of NF3?
B. trigonal pyramidal
Step 1 Draw the electron-dot formula. In the
electron-dot structure for NF3, there are three
electron groups and a lone pair.
F
N
F
F
Solution
What is the shape of a molecule of NF3?
B. trigonal pyramidal
Step 2 Arrange the electron groups around the
central atom to minimize repulsion. The four
electron groups around N would have a
tetrahedral arrangement.
Step 3 Use the atoms bonded to the central atom
to determine the molecular shape. Three
bonding groups and a lone pair give NF3 a
trigonal pyramidal shape with a bond angle of
109.
Next Week
• Clicker Quiz on Chapter 5
• Chapter 6
• Group Assignment Ch5/6