1. Chapter 4 Compounds and Their Bonds
4.5
Covalent Compounds and Their Names
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

2. Covalent Bonds 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.

3. Formation of a Hydrogen Molecule
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.

4. Formation of a Hydrogen Molecule – H2
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.

5. Formation of Octets in Molecules – F2
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.

6. Writing Electron-Dot Formulas
To draw the electron-dot formula for methane, CH4,
we start with the electron-dot symbols for carbon and hydrogen
we need four hydrogen atoms to complete carbon’s octet
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

7. Double and Triple Covalent Bonds
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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

8. Guide to Drawing Electron-Dot Formulas
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

9. Electron-Dot Formulas for Some Covalent Compounds – CO2
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.

10. Electron-Dot Formulas for Some Covalent Compounds – CO2
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.

11. Triple Bond – N2 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.

12. Names and Formulas of Covalent Compounds
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.

13. Guide to Naming Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

14. Prefixes Used in Naming Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

15. Naming Covalent Compounds – NCl3
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.

16. Naming Covalent Compounds – NCl3
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.

17. Some Common Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

18. 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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

19. Solution Select the correct name for each compound.
A. SiCl4 3) silicon tetrachloride
B. P2O5 3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

20. Learning Check 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.

21. Solution 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.

22. Solution 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.

23. Solution 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.

24. Solution 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.

25. Writing Formulas for Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

26. Writing Formulas for Covalent Compounds – Diboron Trioxide
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.

27. Learning Check 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.

28. Solution 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.

29. Solution 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.

30. Solution 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.

31. Summary to Naming Simple Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

32. Learning Check
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.

33. Study Tip: Ionic or Covalent
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.

34. Solution
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. Cu2CO 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.