1. Molecules and Covalent Compounds
The Octet Rule,
Covalent Compounds and Their Names
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Publishing as Benjamin Cummings

2. Valence Electrons Valence electrons
Determine the chemical properties of the elements.
Are the electrons in the highest energy level.
Are related to the Group number of the element.
Example: Phosphorus has 5 valence electrons
5 valence electrons
P Group 5A(15) , 8, 5

3. Groups and Valence Electrons
All the elements in a group have the same
number of valence electrons.
Example: Elements in Group 2A(2) have two (2) valence electrons.
Be 2, 2
Mg 2, 8, 2
Ca 2, 8, 8, 2
Sr 2, 8, 18, 8, 2

4. Periodic Table and Valence Electrons
Representative Elements Group Numbers
H He
Li Be Al C N O F Ne
2,1 2, , , , , , ,8
Li Mg Ge Si P S Cl Ar
2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

5. Learning Check State the number of valence electrons for each: A. O
1) ) 6 3) 8
B. Al
1) ) 3 3) 1
C. Cl
1) 2 2) 5 3) 7

6. Solution State the number of valence electrons for each. A. O 2) 6
2) 6
B. Al
2) 3
C. Cl
3) 7

7. Octet Rule Atoms lose, gain or share valence electrons
in order to achieve noble gas electron
configurations (an octet in the outer shell).
Exception is He that is stable with 2 valence electrons (duet).
valence electrons He
Ne 2,
Ar 2, 8,
Kr 2, 8, 18,

8. Forming Octets Atoms acquire octets By forming compounds.
To become more stable.
By losing, gaining, or sharing valence electrons.
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9. Ionic and Covalent Bonds
Ionic bonds involve
Loss of electrons by a metal.
Gain of electrons by a nonmetal.
Covalent bonds involve
A sharing of electrons.
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10. Forming a H2 Molecule Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings

11. 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 © by Pearson Education, Inc. Publishing as Benjamin Cummings

12. Diatomic Elements
These elements share electrons to form diatomic, covalent molecules.
Table 5.9
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13. Learning Check
What is the name of each of the following diatomic molecules?
H2 ______________________
N2 _______________
Cl2 _______________
O2 _______________
I2 _______________

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

15. Number of Covalent Bonds
The number of covalent bonds can be determined
from the number of electrons needed to complete
an octet.
Table 10.1
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16. 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.
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17. Guide to Writing Electron-Dot Formulas
STEP 1 Determine the arrangement of atoms.
STEP 2 Add the valence electrons from all the atoms.
STEP 3 Attach the central atom to each bonded atom
using one pair of electrons.
STEP 4 Add remaining electrons as lone pairs to
complete octets (2 for H atoms).
STEP 5 If octets are not complete, form one or more
multiple bonds.

18. Electron-Dot Formulas and Models of Some Covalent Compounds
Table 5.10
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19. Names of Covalent Compounds
Prefixes are used
In the names of covalent compounds.
Because two nonmetals can form two or more different compounds.
Examples of compounds of N and O:
NO nitrogen oxide
NO2 nitrogen dioxide
N2O dinitrogen oxide
N2O4 dinitrogen tetroxide
N2O5 dinitrogen pentoxide

20. 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.
Table 5.11
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21. Naming Covalent Compounds
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
The subscript 1(for S) or mono is
understood.

22. Naming Covalent Compounds
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

23. Formulas and Names of Some Covalent Compounds
TABLE 4.13
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24. 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

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

26. Learning Check Write the name of each covalent compound:
PCl3 _____________________
CCl4 _____________________
N2O _____________________

27. Solution Write the name of each covalent compound: CO carbon monoxide
CO2 carbon dioxide
PCl3 phosphorus trichloride
CCl4 carbon tetrachloride
N2O dinitrogen oxide

28. Guide to Writing Formulas
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

29. Learning Check Write the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride

30. Solution 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