4.1 Valence Electrons

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4.1 Valence Electrons

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Chapter 4 Compounds and Their Bonds 4.1 Valence Electrons 4.2 Octet Rule and Ions Valence Electrons The valence electrons are the electrons in the outer shell. – PowerPoint PPT presentation

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Title: 4.1 Valence Electrons

1
Chapter 4 Compounds and Their Bonds

4.1 Valence Electrons
4.2 Octet Rule and Ions

2
Valence Electrons

The valence electrons are the electrons in the
outer shell.
The electrons in the outer shell have the most
contact with other atoms and strongly influence
the chemical properties of atoms.

3
Number of Valence Electrons

For Group A elements, the number of valence
electrons is the number of electrons in the s and
p subshells of the outer shell.
In the electron configuration for phosphorus,
there are 5 valence electrons in the s and p
subshells with the highest number. 5
valence electrons P Group 5A
1s22s22p63s23p3

4
Valence Electrons for Groups

5
Learning Check

State the number of valence electrons for each.
A. Magnesium
1) 2 2) 6 3) 8
B. Oxygen
1) 2 2) 4 3) 6
C. Potassium
1) 1 2) 2 3) 7

6
Solution

State the number of valence electrons for each.
A. Magnesium
1) 2 Group 2A 1s22s22p63s2
B. Oxygen
3) 6 Group 6A 1s22s2 2p4
C. Potassium
1) 1 Group 1A 1s22s22p63s23p64s1

7
Electron Dot Structure

An electron-dot structure is a convenient way to
represent the valence electrons.
For example, the two valence electrons for
magnesium are placed as single dots on any two
sides of the Mg symbol.

8
Electron-Dot Structures

Dot structures are used for Group A elements.
The valence electrons are placed on the sides of
the symbol of an element.

9
Learning Check

?
A. X is the electron dot formula for
1) Na 2) K 3) Al
? ?
B. ? X ? is the electron dot formula of
?
1) B 2) N 3) P

10
Solution

?
A. X is the electron dot formula for
1) Na 2) K
? ?
B. ? X ? is the electron dot formula of
?
2) N 3) P

11
Octet Rule

The stability of the noble gases is associated
with 8 valence electrons (He has 2). Ne 2,
8 Ar 2, 8, 8 Kr 2, 8, 18, 8
Atoms can become more stable by acquiring an
octet (8 electrons) in the outer shell.
The process of acquiring an octet involves the
loss, gain, or sharing of valence electrons.

12
Ionization Energy

Ionization energy is the energy it takes to
remove a valence electron.
Metals have lower ionization energies and
nonmetals have higher ionization energies.

13
Metals Form Positive Ions

Metals acquire octets by losing valence
electrons.
The loss of electrons converts an atom to an ion
that has the electron configuration of the
nearest noble gas.
Metals form positive ions because they have fewer
electrons than protons. Group 1A metals ??
ion 1 Group 2A metals ?? ion 2 Group
3A metals ?? ion 3

14
Learning Check

Give the ionic charge for each ion.
A. 12 p and 10 e-
1) 0 2) 2 3) 2-
B. 50p and 46 e-
1) 2 2) 4 3) 4-
C. 15 p and 18e-
2) 3 2) 3- 3) 5-

15
Solution

Give the ionic charge for each ion.
A. 12 p and 10 e-
2) 2
B. 50p and 46 e-
2) 4
C. 15 p and 18e-
2) 3-

16
Formation of a Sodium Ion, Na

Sodium forms an octet by losing its one valence
electron.
Na ? e? ?? Na
1s22s22p63s1 1s22s22p6 ( Ne)
A positive ion forms with a 1 charge.
Sodium atom Sodium ion
11 p 11 p
11 e- 10 e-
0 1

17
Formation of Mg2

Magnesium forms an octet by losing its two
valence electrons.
Magnesium atom Magnesium ion
?
Mg ? 2e? ?? Mg2
1s22s22p63s2 1s22s22p6 ( Ne)
A positive ion forms with a 2 charge.
12 p 12 p
12 e- 10
e-
0
2

18
Formation of Negative Ions

When nonmetals gain electrons to achieve an octet
arrangement, they form negative ions.
The ionic charge of a nonmetal is 3-, 2-, or 1-.

19
Formation of a Fluoride Ion, F-

Fluorine forms an octet by adding an electron to
its seven valence electrons.
? ? ? ? 1-
F ? e? F
? ? ? ?
1s22s22p5 1s22s22p6 ( Ne)
A negative ion forms with a -1 charge.
Fluorine atom Fluoride ion
9 p 9 p
9 e- 10 e-
0 1

20
Group Number and Ions

The Group number can be used to determine the
charge of an ion.
The charge of a positive ion is equal to its
Group number.
Group 3A 3
The charge of a negative ion is obtained by
subtracting its Group number from 8.
Group 6A - (8-6) 2-

21
Examples of Ionic Charges

22
Some Important Ions in the Body
23
Learning Check

A. How many valence electrons does aluminum have?
1) 2e- 2) 3e- 3) 5e-
B. How does aluminum acquire an octet?
1) loses 3e- 2) gains 3e-
3) gains 5e-
C. What is the ionic charge of an aluminum ion?
1) 3- 2) 5- 3) 3
D. The symbol for the aluminum ion is
1) Al3 2) Al3- 3) Al

24
Solution

A. How many valence electrons does aluminum
have?
2) 3e-
B. How does aluminum acquire an octet?
1) loses 3e-
C. What is the ionic charge of an aluminum ion?
3) 3
D. The symbol for the aluminum ion is
1) Al3

25
Chapter 4 Compounds and Their Bonds

4.3 Ionic Compounds
4.4 Naming and Writing Ionic Formulas

26
Ionic Compounds

Ionic compounds consist of positive and negative
ions.
An ionic bond is an attraction between the
positive and negative charges.
In an ionic formula, the total charge of the
positive ions is equal to the total charge of the
negative ions. total positive charge
total negative charge

27
Ionic Formulas

The formulas of ionic compounds are determined
from the charges on the ions.
atoms ions
? ?
? ?
Na ? ? F ?? Na F ?? NaF
? ?
? ?
sodium fluorine
sodium fluoride
The overall charge of NaF is zero (0).
(1 ) (1-) 0

28
Charge Balance In NaCl

The formula does not show the charges of the ions
in the compound.
The symbol of the metal is written first,
followed by the symbol of the nonmetal.

29
Charge Balance In MgCl2
30
Writing a Formula from Charges

Write the formula of the ionic compound that
forms from Ba2 and Cl?.
Write the symbols of the positive ion and the
negative ion. Ba2 Cl?
Balance the charges until the positive charge is
equal to the negative charge.
Ba2 Cl? two Cl-
needed Cl?
Write the formula using subscripts for the number
of ions for charge balance. BaCl2

31
Learning Check

Write the correct formula for the ionic compound
of
A. Na and S2-
1) NaS 2) Na2S 3) NaS2
B. Al3 and Cl-
1) AlCl3 2) AlCl 3) Al3Cl
C. Mg2 and N3-
1) MgN 2) Mg2N3 3) Mg3N2

32
Solution

A. Na and S2-
2) Na2S
B. Al3 and Cl-
1) AlCl3
C. Mg2 and N3-
3) Mg3N2

33
Names of Ions

Positive ions are named like the element.
Negative ions are named by changing the end of
the element name to ide.

34
Learning Check

Complete the names of the following ions
N3? O2?
F?
_________ __________ _________
P3? S2?
Cl?
_________ __________ _________
Br ?
_________

35
Solution

N3? O2? F?
nitride oxide fluoride
P3? S2? Cl?
phosphide sulfide chloride
Br ?
bromide

36
Naming Ionic Compounds with Two Elements

The name of a binary ionic compound (two
elements) gives the name of the metal ion first
and the name of the negative ion second.
Examples
NaCl sodium chloride
K2S potassium sulfide
CaI2 calcium iodide
Al2O3 aluminum oxide

37
Learning Check

Write the names of the following compounds
1) Na3N ___________
2) KBr ___________
3) Al2S3 ___________
4) MgO ___________

38
Solution

Complete the names of the following compounds
1) Na3N sodium nitride
2) KBr potassium bromide
3) Al2S3 aluminum sulfide
4) MgO magnesium oxide

39
Ionic Charges of Transition Metals

Most transition elements have two or more
positive ions.

40
Summary of Common Ions

Of the transition metals, silver and zinc are
important elements that form only one ion.

41
Learning Check

A. The formula for the ionic compound of
Na and O2- is
1) NaO 2) Na2O 3) NaO2
B. The formula of a compound of aluminum and
chlorine is
1) Al3Cl 2) AlCl2 3) AlCl3
C. The formula of Fe3 and O2- is
1) Fe3O2 2) FeO3 3) Fe2O3

42
Solution

A. The formula for the ionic compound of
Na and O2- is
2) Na2O
B. The formula of a compound of aluminum and
chlorine is
3) AlCl3
C. The formula of Fe3 and O2- is
3) Fe2O3

43
Naming Compounds with Transition Metals

Transition metals with two different ions use a
Roman numeral following the name of the metal to
indicate ionic charge.

44
Learning Check

Select the correct name for each.
A. Fe2S3
1) iron sulfide
2) iron(II) sulfide
3) iron (III) sulfide
B. CuSO4
1) copper sulfate
2) copper(I) sulfate
3) copper (II) sulfate

45
Solution

Select the correct name for each.
A. Fe2S3
3) iron (III) sulfide
B. CuSO4
3) copper (II) sulfate

46
Learning Check

The correct formula is
A. Copper (I) nitride
1) CuN 2) CuN3 3) Cu3N
B. Lead (IV) oxide
1) PbO2 2) PbO 3) Pb2O4

47
Solution

The correct formula is
A. Copper (I) nitride
3) Cu3N
B. Lead (IV) oxide
1) PbO2

48
Chapter 4 Compounds and Their Bonds

4.5 Covalent Bonds
4.6 Naming and Writing Formulas of Covalent
Compounds
4.7 Bond Polarity

49
Covalent Bonds

Covalent bonds form between two nonmetals from
Groups 4A, 5A, 6A, and 7A.
In a covalent bond, electrons are shared to
complete octets.

50
Learning Check

Indicate whether a bond between the following is
1) Ionic 2) Covalent
____A. sodium and oxygen
____B. nitrogen and oxygen
____C. phosphorus and chlorine
____D. calcium and sulfur
____E. chlorine and bromine

51
Solution

Indicate whether a bond between the following is
1) Ionic 2) Covalent
1 A. sodium and oxygen
2 B. nitrogen and oxygen
2 C. phosphorus and chlorine
1 D. calcium and sulfur
2 E. chlorine and bromine

52
H2, A Covalent Molecule

In hydrogen, two hydrogen atoms share their
electrons to form a covalent bond.
Each hydrogen atom acquires a stable outer shell
of two (2) electrons like helium (He).
H? ?H H H H?H H2
hydrogen molecule

53
Diatomic Elements

As elements, the following share electrons to
form diatomic, covalent molecules.

54
Learning Check

What is the name of each of the following
diatomic molecules?
H2 hydrogen
N2 nitrogen
Cl2 _______________
O2 _______________
I2 _______________

55
Solution

What are the names of each of the following
diatomic molecules?
H2 hydrogen
N2 nitrogen
Cl2 chlorine
O2 oxygen
I2 iodine

56
Covalent Bonds in NH3

The compound NH3 consists of a N atom and three H
atoms.
? ?
? N ? and 3 H ?
?
By sharing electrons to form NH3, the electron
dot structure is written as
H Bonding pairs
? ?
H N H
? ? Lone
pair of electrons

57
Number of Covalent Bonds

Often, the number of covalent bonds formed by a
nonmetal is equal to the number of electrons
needed to complete the octet.

58
Dot Structures and Models of Some Covalent
Compounds

59
Multiple Bonds

Sharing one pair of electrons is a single
bond. X X or XX
In multiple bonds, two pairs of electrons are
shared to form a double bond or three pairs of
electrons are shared in a triple bond. X X
or X X X X or X X

60
Multiple Bonds in N2

In nitrogen, octets are achieved by sharing three
pairs of electrons.
When three pairs of electrons are shared, the
multiple bond is called a triple bond.
octets
? ? ? ?
? ? ? ?
? N ? ? N ? ?? NN
? ?
triple bond

61
Naming Covalent Compounds

In the name of a covalent compound, the first
nonmetal is named followed by the name of the
second nonmetal ending in ide.
Prefixes indicate the number of atoms of each
element.

62
Learning Check

Complete the name of each covalent compound
CO carbon ______oxide
CO2 carbon _______________
PCl3 phosphorus ___________
CCl4 carbon _______________
N2O ______________________

63
Solution

Complete the name of each covalent compound
CO carbon monoxide
CO2 carbon dioxide
PCl3 phosphorus trichloride
CCl4 carbon tetrachloride
N2O dinitrogen monoxide

64
Formulas and Names of Some Covalent Compounds

65
Learning Check

Select the correct name for each compound.
A. SiCl4 1) silicon chloride
2) tetrasilicon chloride
3) silicon tetrachloride
B. P2O5 1) phosphorus oxide
2) phosphorus pentoxide
3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
2) dichlorine oxide
3) chlorine heptoxide

66
Solution

Select the correct name for each compound.
A. SiCl4 3) silicon tetrachloride
B. P2O5 3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide

67
Electronegativity

Electronegativity is the attraction of an atom
for shared electrons.
The nonmetals have high electronegativity values
with fluorine as the highest.
The metals have low electronegativity values.

68
Some Electronegativity Values for Group A Elements

69
Nonpolar Covalent Bonds

The atoms in a nonpolar covalent bond have
electronegativity differences of 0.3 or less.
Examples Atoms Electronegativity Type
of Difference Bond N-N 3.0 - 3.0
0.0 Nonpolar covalentCl-Br 3.0 - 2.8 0.2
Nonpolar covalentH-Si 2.1 - 1.8 0.3
Nonpolar covalent

70
Polar Covalent Bonds

The atoms in a polar covalent bond have
electronegativity differences of 0.4 to 1.6.
Examples Atoms Electronegativity Type
of Difference BondO-Cl 3.5 - 3.0 0.5
Polar covalentCl-C 3.0 - 2.5 0.5 Polar
covalentO-S 3.5 - 2.5 1.0 Polar covalent

71
Comparing Nonpolar and Polar Covalent Bonds

72
Ionic Bonds

The atoms in an ionic bond have electronegativity
differences of 1.7 or more.
Examples Atoms Electronegativity Type
of Difference BondCl-K 3.0 0.8
2.2 IonicN-Na 3.0 0.9 2.1 IonicS-Cs 2.5
0.7 1.8 Ionic

73
Range of Bond Types

74
Predicting Bond Type
75
Learning Check

Identify the type of bond between the following
as
1) nonpolar covalent
2) polar covalent
3) ionic
A. K-N
B. N-O
C. Cl-Cl

76
Solution

A. K-N
3) ionic
B. N-O
2) polar covalent
C. Cl-Cl
1) nonpolar covalent

77
Chapter 4 Compounds and Their Bonds

4.8 Polyatomic Ions

78
Polyatomic Ions

A polyatomic ion is a group of two or more atoms
that has an overall ionic charge.
Some examples of polyatomic ions are
NH4 ammonium OH - hydroxide
NO3- nitrate NO2 - nitrite
CO32 - carbonate PO43 - phosphate
HCO3 - hydrogen carbonate (bicarbonate)

79
Common Polyatomic Ions

80
Formulas with Polyatomic Ions

The formula of an ionic compound containing a
polyatomic ion is written to make the overall
charge equal zero (0).
Na and NO3- NaNO3
When two or more polyatomic ions are needed, the
polyatomic ion is enclosed in parentheses.
polyatomic ion
Mg2 and NO3 - Mg(NO3)2
subscript 2 for charge balance

81
Some Compounds with Polyatomic Ions

82
Learning Check

Select the correct formula for each
A. Aluminum nitrate
1) AlNO3 2) Al(NO)3 3)
Al(NO3)3
B. Copper(II) nitrate
1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)
C. Iron (III) hydroxide
1) FeOH 2) Fe3OH 3) Fe(OH)3
D. Tin(IV) hydroxide
1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)

83
Solution

Select the correct formula for each
A. Aluminum nitrate
3) Al(NO3)3
B. Copper(II) nitrate
2) Cu(NO3)2
C. Iron (III) hydroxide
3) Fe(OH)3
D. Tin(IV) hydroxide
1) Sn(OH)4

84
Naming Compounds with Polyatomic Ions

For compounds with polyatomic ions, the positive
ion is named first followed by the name of the
polyatomic ion.NaNO3 sodium nitrateK2SO4 potas
sium sulfateAl(HCO3)3 aluminum bicarbonate or
aluminum hydrogen carbonate(NH4)3PO4 ammonium
phosphate

85
Learning Check

Match each formula with the correct name
A. Na2CO3 1) magnesium sulfite
MgSO3 2) magnesium sulfate
MgSO4 3) sodium carbonate
B. Ca(HCO3)2 1) calcium carbonate
CaCO3 2) calcium phosphate
Ca3(PO4)2 3) calcium bicarbonate

86
Solution

A. Na2CO3 3) sodium carbonate
MgSO3 1) magnesium sulfite
MgSO4 2) magnesium sulfate
B. Ca(HCO3)2 3) calcium bicarbonate
CaCO3 1) calcium carbonate
Ca3(PO4)2 2) calcium phosphate

87
Summary of Naming Compounds
88
Naming Rules
89
Naming Rules (continued)
90
Learning Check

Name each of the following compounds
A. Mg(NO3)2
B. CuCl2
C. N2O4
D. Fe2(SO4)3
E. Ba3(PO4)2

91
Solution

Name each of the following compounds
A. Mg(NO3)2 magnesium nitrate
B. CuCl2 copper(II) chloride
C. N2O4 dinitrogen tetroxide
D. Fe2(SO4)3 iron(III) sulfate
E. Ba3(PO4)2 barium phosphate

92
Learning Check

Write the correct formula for each
A. potassium sulfide
B. calcium carbonate
C. sodium phosphite
D. iron(III) oxide
E. iron (II) nitrate

93
Solution

Write the correct formula for each
A. potassium sulfide K2S
B. calcium carbonate CaCO3
C. sodium phosphite Na3PO3
D. iron(III) oxide Fe2O3
E. iron (II) nitrate Fe(NO3)2

94
Chapter 4 Compounds and Their Bonds

4.9 Shapes of Molecules
4.10 Polar and Nonpolar Molecules

95
VSEPR

The shape of a molecule is predicted from the
geometry of the electrons pairs around the
central atom.
In the valence-shell electron-pair repulsion
theory (VSEPR), the electron pairs are arranged
as far apart as possible to give the least amount
of repulsion of the negatively charged electrons.

96
Two Electron Pairs

In a molecule of BeCl2, there are two bonding
pairs around the central atom Be. (Be is an
exception to the octet rule.)
The arrangement of two electron pairs to
minimize their repulsion is 180 or opposite each
other.
The shape of the molecule is linear.

97
Two Electron Pairs with Double Bonds

The electron-dot structure for CO2 consists of
two double bonds to the central atom C.
Because the electrons in a double bond are held
together, a double bond is counted as a single
unit.
Repulsion is minimized when the double bonds are
placed opposite each other at 180 to give a
linear shape.

98
Three Electron Pairs

In BF3, there are 3 electron pairs around the
central atom B. (B is an exception to the octet
rule.)
Repulsion is minimized by placing three electron
pairs in a plane at angles of 120, which is a
trigonal planar arrangement.
The shape with three bonded atoms is trigonal
planar.

99
Two Bonding Pairs and A Nonbonding Pair

In SO2, there are 3 electron units around the
central atom S.
Two electron units are bonded to atoms and one
electron pair is a nonbonding pair.
Repulsion is minimized by placing three electron
pairs in a plane at angles of 120, which is
trigonal planar.
The shape with two bonded atoms is bent.

100
Learning Check

The shape of a molecule of N2O (N N O) is
1) linear
2) trigonal planar
3) bent (120)

101
Solution

The shape of a molecule of N2O (N N O) is
1) linear
The electron-dot structure uses 5 e for each N
and 6 e for O (16 e total) has octets using two
double bond to the central N and one nonbonding
pair. The shape with two bonded atoms is linear.
N N O

102
Four Electron Pairs

In CH4, there are 4 electron pairs around the
central atom C.
Repulsion is minimized by placing four electron
pairs at angles of 109, which is a tetrahedral
arrangement.
The shape with four bonded atoms is called
tetrahedral.

103
Three Bonding Atoms and One Nonbonding Pair

In NH3, there are 4 electron pairs around the N.
Three pairs are bonded to atoms and one is a
nonbonding pair.
Repulsion is minimized by placing four electron
pairs at angles of 109, which is a tetrahedral
arrangement.
The shape with three bonded atoms is pyramidal.

104
Two Bonding Atoms and Two Lone Pairs

In H2O, there are 4 electron pairs around O.
Two pairs are bonded to atoms and two are
nonbonding pairs.
Repulsion is minimized by placing four electron
pairs at angles of 109 called a tetrahedral
arrangement.
The shape with two bonded atoms is called bent.

105
Some Steps Using VSEPR to Predict Shape

Draw the electron dot structure.
Count the electron pairs around the central atom.
Arrange the electron pairs to minimize repulsion.
Determine the shape using the number of bonded
atoms in the electron arrangement.

106
Summary of Electron Arrangements and Shapes

107
Learning Check