CH_4_5_Covalent_Compounds_and_Names

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Chapter 4
Compounds and Their Bonds
1
4.5
Covalent Compounds and Their
Names
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Covalent Bonds
2
Covalent compounds form
•
when atoms share electrons to complete octets
•
between nonmetal atoms from Groups 4A, 5A, 6A, and 7A
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Formation of a Hydrogen Molecule
3
A hydrogen molecule, H2,
• forms as the atoms move closer and the nucleus of one
atom attracts the electron of the other
• is stable with 2 electrons (helium)
• has a shared pair of electrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Formation of a Hydrogen Molecule – H2
4
A covalent bond forms
as H atoms move
close together to share
electrons.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Formation of Octets in Molecules – F2
5
In a fluorine, F2,, molecule, each F atom shares one electron to
attain an octet.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Writing Electron-Dot Formulas
6
To draw the electron-dot formula
for methane, CH4,
• we start with the electron-dot
symbols for carbon and
hydrogen
C
H
H C H
H
H
H
we need four hydrogen atoms to
complete carbon’s octet
•
H
C
H
H
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Double and Triple Covalent Bonds
7
A double bond:
• occurs when atoms share two pairs of electrons
• forms when there are not enough electrons to complete
octets
A triple bond:
• occurs when atoms share three pairs of electrons
• forms when there are not enough electrons to complete
octets
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Guide to Drawing Electron-Dot
Formulas
8
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Electron-Dot Formulas for Some
Covalent Compounds – CO2
9
Step 1 Determine the arrangement of atoms. O C O
Step 2 Determine the total number of valence electrons.
C
2(O) = CO2
4e− + 2(6−) = 16e−
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Electron-Dot Formulas for Some
Covalent Compounds – CO2
10
Step 3 Attach each bonded atom to the central atom
with a pair of electrons.
Step 4 Place the remaining electrons using single or
multiple bonds to complete octets.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Triple Bond – N2
11
In a nitrogen molecule, N2,
•
•
•
each N atom shares three electrons to gain an octet
the multiple bond formed is called a triple bond
the name is the same as the element
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Names and Formulas of Covalent
Compounds
12
When naming covalent compounds:
• the first nonmetal in the formula is named by its element
name
• the second nonmetal is named by using the first syllable
of its name followed by ide
• if a subscript is used in the formula a prefix is used in
front of its name
• when vowels o and o or a and o appear together, the first
vowel is omitted
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Guide to Naming Covalent Compounds
13
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Prefixes Used in Naming Covalent
Compounds
14
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Naming Covalent Compounds – NCl3
15
Name the covalent compound NCl3.
Step 1 Name the first nonmetal by its element name.
The first nonmetal (N) is nitrogen.
Step 2 Name the second element by using the first
syllable of its name followed by ide.
The second nonmetal (Cl) is chloride.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Naming Covalent Compounds – NCl3
16
Step 3 Add prefixes to indicate number of atoms.
Because there is one nitrogen atom, no prefix
is needed.
The subscript three for the Cl atoms is shown as the
prefix tri.
NCl3, nitrogen trichloride
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Some Common Covalent Compounds
17
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
18
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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
19
Select the correct name for each compound.
A.
B.
C.
SiCl4
P2O5
Cl2O7
3) silicon tetrachloride
3) diphosphorus pentoxide
1) dichlorine heptoxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
20
Write the name of each covalent compound.
A. CO
B. NO2
C. PF3
D. CCl4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
21
Write the name of each covalent compound.
Step 1 Name the first nonmetal by its element name.
A. CO
The first nonmetal (C) is carbon.
B. NO2
The first nonmetal (N) is nitrogen.
C. PF3
The first nonmetal (P) is phosphorus.
D. CCl4
The first nonmetal (C) is carbon.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
22
Write the name of each covalent compound.
Step 2 Name the second element by using the first
syllable of its name followed by ide.
A. CO
The second nonmetal (O) is oxide.
B. NO2
The second nonmetal (O) is oxide.
C. PF3
The second nonmetal (F) is fluoride.
D. CCl4
The second nonmetal (Cl) is chloride.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
23
Write the name of each covalent compound.
Step 3 Add prefixes to indicate number of atoms.
A. CO Because there is one carbon atom, no prefix is
needed. The subscript 1 for the O atom is
shown using the prefix mono.
CO is carbon monoxide.
B. NO2 Because there is one nitrogen atom, no prefix is
needed. The subscript 2 for the O atoms is
shown using the prefix di.
NO2 is nitrogen dioxide.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
24
Write the name of each covalent compound.
Step 3 Add prefixes to indicate number of atoms.
C. PF3 Because there is one phosphorus atom, no
prefix is needed. The subscript 3 for F atoms
is shown using the prefix tri.
PF3 is phosphorus trifluoride.
D. CCl4 Because there is one carbon atom, no prefix is
needed. The subscript 4 for the Cl atoms is
shown using the prefix tetra.
CCl4 is carbon tetrachloride.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Writing Formulas for Covalent
Compounds
25
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Writing Formulas for Covalent
Compounds – Diboron Trioxide
26
Write the formula for the covalent compound diboron trioxide.
Step 1 Write the symbols in order of the elements in
the name.
The first nonmetal is boron (B) and the second nonmetal
is oxygen (O). B O
Step 2 Write any prefixes as subscripts.
The prefix di in diboron indicates there are two boron
atoms and is shown as a subscript after B. The
prefix tri in trioxide indicates there are three oxygen atoms
and is shown as a subscript after O. B2O3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
27
Write the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
28
Write the correct formula for each of the following:
Step 1 Write the symbols in order of the elements in the name.
A. phosphorus pentachloride
The first nonmetal is phosphorus, (P) and the second
nonmetal is chlorine, (Cl). P Cl
B. dinitrogen trioxide
The first nonmetal is nitrogen, (N) and the second
nonmetal is oxygen, (O). N O
C. sulfur hexafluoride
The first nonmetal is sulfur, (S) and the second
nonmetal is fluorine, (F). S F
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
29
Write the correct formula for each of the following:
Step 2 Write any prefixes as subscripts.
A. phosphorus pentachloride: No prefix for
phosphorus indicates there is 1 phosphorus
atom. The prefix penta in pentachloride
indicates there are 5 chlorine atoms, and is
shown as a subscript after Cl. PCl5
B. dinitrogen trioxide: The prefix di in dinitrogen
indicates there are 2 nitrogen atoms and is
shown as a subscript after N. The prefix tri in
trioxide indicates there are 3 oxygen atoms and is
shown as a subscript after O. N2O3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
30
Write the correct formula for each of the following:
Step 2 Write any prefixes as subscripts.
C. sulfur hexafluoride: No prefix for sulfur
indicates there is 1 sulfur atom. The prefix
hexa in hexafluoride indicates there are 6
fluorine atoms and is shown as a subscript
after F. SF6
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Summary to Naming Simple
Compounds
31
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
32
Identify each compound as ionic or covalent, and give its
correct name.
A. SO3
B. BaCl2
C. (NH4)3PO3
D. Cu2CO3
E. N2O4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Study Tip: Ionic or Covalent
33
A compound is
• ionic if the first element in the formula or the name is a metal
or the polyatomic ion NH4+
K2O K is a metal; compound is ionic; potassium
oxide
• covalent if the first element in the formula or the name is a
nonmetal
N2O N is a nonmetal; compound is covalent;
dinitrogen oxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
34
Identify each compound as ionic or covalent and give its
correct name.
A. SO3
covalent – sulfur trioxide
B. BaCl2
ionic – barium chloride
C. (NH4)3PO3
ionic – ammonium phosphite
D. Cu2CO3
ionic – copper(I) carbonate
E. N2O4
covalent – dinitrogen tetroxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
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