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1
Chapter 5 Molecules and Covalent Compounds
5.5
Covalent Compounds and Their Names
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
3
H2, A Covalent Molecule
In a hydrogen (H2) molecule
• Two hydrogen atoms share electrons to form a covalent single bond.
• Each H atom acquires two (2) electrons.
• Each H becomes stable like helium (He).
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
4
Diatomic Elements
• These elements share electrons to form diatomic, covalent molecules.Table 5.9
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
5
What is the name of each of the following diatomic molecules?
H2 ______________________
N2 _______________
Cl2 _______________
O2 _______________
I2 _______________
Learning Check
6
What are the names of each of the following diatomic molecules?
H2 hydrogen
N2 nitrogen
Cl2 chlorine
O2 oxygen
I2 iodine
Solution
7
Electron-Dot Formulas
Electron-dot formulas show
• The order of bonded atoms in a covalent compound.
• The bonding pairs of electrons between atoms.
• The unshared (lone) valence electrons.
• A central atom with an octet.
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
8
Electron-Dot Formulas and Models of Some Covalent Compounds
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Table 5.10
9
Names of Covalent Compounds
Prefixes are used• In the names of covalent compounds.• Because two nonmetals can form two or more different
compounds.
• If the element begins with a vowel then the vowel on the prefix is omitted.• E.g., Carbon mono-oxide becomes
Carbon monoxide
Exception – the vowel “i” is kept
E.g., Boron tri-iodide becomes
Boron triiodide
10
Naming Covalent Compounds
STEP 1 Name the first nonmetal as the element.
STEP 2 End the name of the
second nonmetal
with -ide
STEP 3 Use prefixes to show the number of
atoms (subscripts).
* Mono is usually omitted for the first element but used for the second.
Table 5.11
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Examples
Examples of compounds of N and O:
NO nitrogen monoxide
NO2 nitrogen dioxide
N2O dinitrogen oxide
N2O4 dinitrogen tetroxide
N2O5dinitrogen pentoxide
11
12
What is the name of SO3?
STEP 1 The first nonmetal is S sulfur.
STEP 2 The second nonmetal is O named oxide.
STEP 3 The subscript 3 of O is shown as the prefix tri.
SO3 → sulfur trioxide
Remember not to use mono for the first
element!!
Naming Covalent Compounds
13
Name P4S3
STEP 1 The first nonmetal P is phosphorus.
STEP 2 The second nonmetal S is sulfide.
STEP 3 The subscript 4 of P is shown as tetra.
The subscript 3 of O is shown as tri.
P4S3 → tetraphosphorus trisulfide
Naming Covalent Compounds
14
Formulas and Names of Some Covalent Compounds
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
TABLE 4.13
15
Select the correct name for each compound.
A. SiCl4 1) silicon chloride
2) tetrasilicon chloride3) silicon tetrachloride
B. P2O5 1) phosphorus oxide
2) phosphorus pentoxide3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
2) dichlorine oxide3) chlorine heptoxide
Learning Check
16
Select the correct name for each compound.
A. SiCl4 3) silicon tetrachloride
B. P2O5 3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
Solution
17
Write the name of each covalent compound:
CO _____________________
CO2 _____________________
PCl3 _____________________
CCl4 _____________________
N2O _____________________
Learning Check
18
Write the name of each covalent compound:
CO carbon monoxide
CO2 carbon dioxide
PCl3 phosphorus trichloride
CCl4 carbon tetrachloride
N2O dinitrogen oxide
Solution
19
STEP 1 Write the symbols in the order of the
elements in the name.
STEP 2 Write any prefixes as subscripts.
Example: Write the formula for carbon disulfide.
STEP 1 Elements are C and S
STEP 2 No prefix for carbon means 1 C
Prefix di = 2
Formula: CS2
Guide to Writing Formulas
20
Write the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride
Learning Check
21
Write the correct formula for each of the following:
A. phosphorus pentachloride
1 P penta = 5 Cl PCl5
B. dinitrogen trioxide
di = 2 N tri = 3 O N2O3
C. sulfur hexafluoride
1 S hexa = 6 F SF6
Solution
22
Learning Check
Identify each compound as ionic or covalent and
give its correct name.
A. SO3
B. MnCl2
C. (NH4)3PO4
D. Cu2CO3
E. N2O4
23
SolutionIdentify each compound as ionic or covalent and
give its correct name.
A. SO3 covalent - sulfur trioxide
B. MnCl2 ionic - manganese(II) chloride
C. (NH4)3PO3 ionic - ammonium phosphite
D. Cu2CO3 ionic – copper(I) carbonate
E. N2O4 covalent – dinitrogen tetroxide
24
Learning Check
Identify each compound as ionic or covalent and
give its correct name.
A. Ca3(PO4)2
B. FeBr3
C. SCl2
D. Cl2O