1. 6.5 Molecular Compounds: Sharing Electrons
The names of molecular compounds need prefixes because several different compounds can be formed from the same two nonmetals.
Learning Goal Given the formula of a molecular compound, write its correct name; given the name of a molecular compound, write its formula.

2. Covalent Bonds Molecular compounds form when
atoms of two or more nonmetals share electrons and form a covalent bond.
valence electrons are shared by nonmetal atoms to achieve stability.
A molecule forms when two or more atoms share electrons.
Core Chemistry Skill Writing the Names and Formulas for Molecular Compounds

3. Names and Formulas, Molecular Compounds
When naming a molecular compound, the
first nonmetal in the formula is named by its element name.
second nonmetal is named using the first syllable of the name followed by ide.
When a subscript indicates two or more atoms of an element, a prefix is shown in front of its name.

4. Names and Formulas, Molecular Compounds
Several compounds may be formed from the same two nonmetals:
CO2 = carbon dioxide
CO = carbon monoxide
The number of oxygen atoms present is indicated by the prefix.
When the vowels o and o or a and o appear together, the first vowel is omitted.
NO = nitrogen monoxide,

5. Common Molecular Compounds

6. Guide to Naming Molecular Compounds

7. Naming Molecular Compounds, NCl3
Name the molecular compound NCl3. STEP 1 Name the first nonmetal by its element name. In NCl3, the first nonmetal (N) is nitrogen.
Symbol of the Element N Cl
ANALYZE THE Name nitrogen chloride PROBLEM Subscript
Prefix none tri

8. Naming Molecular Compounds, NCl3
Name the molecular compound NCl3. STEP 2 Name the second nonmetal by using the first syllable of the element name followed by ide. In NCl3, the second nonmetal (Cl) is chloride. STEP 3 Add prefixes to indicate the number of atoms (subscripts). Because there is one nitrogen atom, no prefix is needed. The subscript 3 for the Cl atoms is shown as the prefix tri. The name of NCl3 is nitrogen trichloride.

9. Study Check
Name the molecular compound B2O3.

10. Solution
Name the molecular compound B2O3. STEP 1 Name the first nonmetal by its element name. In B2O3, the first nonmetal (B) is boron. STEP 2 Name the second nonmetal by using the first name followed by ide. The name of the second nonmetal (O) is oxide.
Symbol of the Element B O
ANALYZE THE Name boron oxide PROBLEM Subscript 2 3
Prefix di tri

11. Solution
Name the molecular compound B2O3. STEP 3 Add prefixes to indicate the number of atoms (subscripts). In B2O3, the first nonmetal (B) has the subscript of 2, which is shown as the prefix di. The subscript of 3 for the O atoms is shown as the prefix tri. The name of B2O3 is diboron trioxide.

12. Guide to Writing Formulas from the Names of Molecular Compounds

13. Study Check
Write the molecular formula for diphosphorus pentoxide.

14. Solution
Write the molecular formula for diphosphorus pentoxide. STEP 1 Write the symbols in the order of the elements in the name. STEP 2 Write any prefixes as subscripts. The prefix di in diphosphorus indicates there are two phosphorus atoms. The prefix penta in pentoxide indicates there are five oxygen atoms. P2O5

15. Compounds, Ionic or Covalent?
A compound is usually
ionic if the first element in the formula or the name is a metal or the polyatomic ion NH4+.
K2O: K is a metal; the compound is ionic. potassium oxide
covalent if the first element in the formula is a nonmetal.
N2O: N is a nonmetal; the compound is covalent. dinitrogen oxide

16. Flowchart, Naming Compounds

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

18. Solution
Select the correct name for each compound. 1. SiCl4 C. silicon tetrachloride 2. P2O5 C. diphosphorus pentoxide 3. Cl2O7 A. dichlorine heptoxide

19. Study Check
Identify each compound as ionic or covalent and give its correct name. A. SO3 B. BaCl2 C. (NH4)3PO3 D. Cu2CO3 E. N2O4

20. 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. Cu2CO3 ionic – copper(I) carbonate E. N2O4 covalent – dinitrogen tetroxide