Question

. writing formulas from names
before you begin, do the following:
#1 circle the numbers for all of the covalent compounds. do all of these first, or do them last.
#2 write the symbol and charge above every ion in the ionic compounds (all the ones not circled).

1. lithium oxide ______
2. aluminum sulfide ______
3. calcium chloride ______
4. dinitrogen pentaoxide ______
5. carbon tetrahydride ______
6. dihydrogen monoxide ______
7. sodium chloride ______
8. silver sulfide ______

Explanation:

Step 1: Identify Covalent Compounds

Covalent compounds are made of non - metals (or non - metal and metalloid). Let's analyze each compound:

• Lithium oxide: Lithium is a metal, oxygen is a non - metal. Ionic (metal - non - metal).
• Aluminum sulfide: Aluminum is a metal, sulfur is a non - metal. Ionic.
• Calcium chloride: Calcium is a metal, chlorine is a non - metal. Ionic.
• Dinitrogen pentaoxide: Nitrogen and oxygen are non - metals. Covalent. Circle 4.
• Carbon tetrahydride (methane): Carbon and hydrogen are non - metals. Covalent. Circle 5.
• Dihydrogen monoxide (water): Hydrogen and oxygen are non - metals. Covalent. Circle 6.
• Sodium chloride: Sodium is a metal, chlorine is a non - metal. Ionic.
• Silver sulfide: Silver is a metal, sulfur is a non - metal. Ionic.

Step 2: Write Formulas for Ionic Compounds (Using Criss - Cross Method)

1. Lithium Oxide

• Lithium ion: $Li^{+}$, Oxide ion: $O^{2 - }$
• Criss - cross the charges: Lithium has a charge of + 1, oxide has - 2. So formula is $Li_2O$

2. Aluminum Sulfide

• Aluminum ion: $Al^{3+}$, Sulfide ion: $S^{2 - }$
• Criss - cross: $Al_2S_3$

3. Calcium Chloride

• Calcium ion: $Ca^{2+}$, Chloride ion: $Cl^{-}$
• Criss - cross: $CaCl_2$

7. Sodium Chloride

• Sodium ion: $Na^{+}$, Chloride ion: $Cl^{-}$
• Formula: $NaCl$

8. Silver Sulfide

• Silver ion: $Ag^{+}$ (silver has a + 1 charge in sulfide), Sulfide ion: $S^{2 - }$
• Criss - cross: $Ag_2S$

Step 3: Write Formulas for Covalent Compounds (Using Prefixes)

4. Dinitrogen Pentaoxide

• Prefix "di" for nitrogen means 2, "penta" for oxygen means 5. Formula: $N_2O_5$

5. Carbon Tetrahydride

• Prefix "tetra" for hydrogen means 4. Carbon is 1 (no prefix). Formula: $CH_4$ (since carbon tetrahydride is methane, $C + 4H$)

6. Dihydrogen Monoxide

• Prefix "di" for hydrogen means 2, "mono" for oxygen means 1. Formula: $H_2O$

Answer:

Part 1 (Circling Covalent Compounds)

Circled numbers: 4 (dinitrogen pentaoxide), 5 (carbon tetrahydride), 6 (dihydrogen monoxide)

Part 2 (Formulas)

1. Lithium oxide: $\boldsymbol{Li_2O}$
2. Aluminum sulfide: $\boldsymbol{Al_2S_3}$
3. Calcium chloride: $\boldsymbol{CaCl_2}$
4. Dinitrogen pentaoxide: $\boldsymbol{N_2O_5}$
5. Carbon tetrahydride: $\boldsymbol{CH_4}$
6. Dihydrogen monoxide: $\boldsymbol{H_2O}$
7. Sodium chloride: $\boldsymbol{NaCl}$
8. Silver sulfide: $\boldsymbol{Ag_2S}$