Naming Binary Ionic Compounds and Multivalent Metals Study Guide

Identification of Ionic Compounds

• There are two primary ways to identify a chemical compound:

  • Chemical Name: The written name of the substance (e.g., Magnesium Phosphide).

  • Chemical Formula: The symbolic representation of the elements and their ratios (e.g., $MgCl_2$).

Rules for Naming Binary Ionic Compounds

• To correctly name a binary ionic compound, follow this specific order of identification and modification:

• First Step: Identify the positive ion, which is always the metal cation. The name of the metal remains unchanged.

• Second Step: Identify the second part of the name, which is the negative ion, also known as the non-metal anion.

• Third Step: Modify the suffix of the negative ion/non-metal anion. The ending of the non-metal must be changed to $-ide$.

• Examples of Naming Transformation:

  • Magnesium and Phosphorus: This combination becomes Magnesium Phosphide.

  • Sodium and Chlorine: This combination becomes Sodium Chloride.

  • Calcium and Bromine: This combination becomes Calcium Bromide.

  • Aluminum and Oxygen: This combination becomes Aluminum Oxide.

Writing Chemical Formulas for Ionic Compounds

• When writing the chemical formula for an ionic compound, certain structural rules apply:

• Element Symbols: List the metal symbol first, followed by the non-metal symbol.

• Determining Charges: Charges for each element are required and can be found in the top right corner of the element's square on the periodic table.

• The Flip-Flop Method: To determine the subscripts for the formula, the numerical values of the charges are swapped (cross-multiplied) to the opposite element.

• Handling One (1): If the resulting charge or subscript is $1$, it is dropped and not written in the final chemical formula.

Determining Ionic Charges from the Periodic Table

• The ionic charge of an element is determined by the group number in which it is located on the periodic table. The common charges are mapped as follows:

  • Group 1: $+1$

  • Group 2: $+2$

  • Group 13: $+3$

  • Group 14: $+4$

  • Group 15: $-3$

  • Group 16: $-2$

  • Group 17: $-1$

Comprehensive Example: Magnesium Chloride

• To find the chemical formula for Magnesium Chloride, evaluate the components:

  • Identify Symbols: Magnesium is $Mg$; Chlorine is $Cl$.

  • Identify Charges: Magnesium has a charge of $2+$ ($Mg^{2+}$). Chlorine has a charge of $1-$ ($Cl^{1-}$).

  • Apply Flip-Flop: Cross the numbers so the $2$ from Magnesium moves to Chlorine, and the $1$ from Chlorine moves to Magnesium.

  • Intermediate Representation: $Mg_1Cl_2$.

  • Final Result: Since we do not need the number $1$, the official chemical formula is $MgCl_2$.

Understanding Multivalent Metals

• When checking the periodic table, you may notice that some elements possess more than one possible charge. These elements are categorized as MULTIVALENT METALS.

• Example: Copper ($Cu$) is a multivalent metal because it can form ions with either a charge of $+1$ or a charge of $+2$.

Naming Compounds with Multivalent Metals

• Because multivalent metals have multiple possible charges, the chemical name must specify which charge is being used in that particular compound.

• Roman Numerals: A Roman numeral must be included in parentheses immediately following the metal's name to indicate the ion's charge.

• Example: Copper (II) Sulfide indicates that the copper ion involved has a charge of $+2$. Its formula is $CuS$.

Step-by-Step Procedure for Naming Multivalent Ionic Compounds

• To name a compound like $Cu_3N$ or $SnS_2$, follow these eight steps:

1. Identify the Metal:

   • For $Cu_3N$, the metal is Copper ($Cu$).

   • For $SnS_2$, the metal is Tin ($Sn$).

2. Check for Multivalence: Determine if the metal has more than one charge on the periodic table.

   • Copper can be $Cu^{+1}$ or $Cu^{+2}$.

   • Tin can be $Sn^{+2}$ or $Sn^{+4}$.

3. Count the Ions: Determine how many of each ion are present in the formula.

   • In $Cu_3N$, there are $3$ Copper ions and $1$ Nitrogen ion.

   • In $SnS_2$, there is $1$ Tin ion and $2$ Sulfur ions.

4. Note the Non-Metal Charge:

   • Nitrogen has a charge of $-3$.

   • Sulfur has a charge of $-2$.

5. Balance Charges (Net Zero): The total negative and positive charges must balance to equal zero.

   • For $Cu_3N$: The negative charges equal $-3$, so the total positive charges must equal $+3$.

   • For $SnS_2$: Two sulfur ions at $-2$ each equal a total negative charge of $-4$, so the total positive charges must equal $+4$.

6. Determine Metal Ion Charge:

   • For Copper: $3 \times (Cu?) = 3+$. Therefore, the charge on each individual Copper ion must be $+1$.

   • For Tin: $1 \times (Sn?) = +4$. Therefore, the charge on the single Tin ion must be $4+$.

7. Write the Metal Ion Name:

   • This results in Copper (I) and Tin (IV).

8. Write the Full Compound Name:

   • The final names are Copper (I) Nitride and Tin (IV) Sulfide.

In-Depth Analysis: Tin (IV) Phosphide ($Sn_3P_4$)

• Breakdown of the steps for the formula $Sn_3P_4$:

1. Metal: Tin.

2. Multivalent?: Yes, Tin has both $Sn^{+2}$ and $Sn^{+4}$ possibilities.

3. Ion Counts: There are $3$ Tin ions and $4$ Phosphorus ions.

4. Non-Metal Charge: Phosphorus has a charge of $-3$.

5. Charge Balancing: Total negative charge is $4 \times (-3) = -12$. Therefore, total positive charge must be $+12$.

6. Determine Charge per Metal Ion: $3 \times (Sn?) = 12+$. Dividing $12$ by $3$ gives a charge of $+4$ per Tin atom.

7. Metal Name: Tin (IV).

8. Full Compound Name: Tin (IV) Phosphide.

The Box Method for Determining Valence

• An alternative visualization to determine the valence/charge of a metal in a compound:

1. Write the Chemical Formula: Start with the known formula (e.g., $Cu_2(CO_3)$).

2. Draw a T-Chart: Create a chart separating the cation (metal) from the anion (non-metal or polyatomic ion).

3. Identify Anion Charge: Determine the ionic charge of the non-metal/anion (e.g., for Cardonate ($CO_3$), the charge is $-2$).

4. Multiply by Subscript: Multiply the anion charge by its subscript. In $Cu_2(CO_3)$, there is an "imaginary 1" after the carbonate. So, $-2 \times 1 = -2$. Write this in the box below the anion.

5. Flip the Sign: Change the negative sign to a positive sign to find the total positive charge required (e.g., $-2$ becomes $+2$).

6. Divide by Metal Subscript: Divide this positive number by the subscript following the metal. In $Cu_2(CO_3)$, the subscript for Copper is $2$.

   • Calculation: $2 \times 2 = 1$. (Note: Transcript intended to say $2 \text{ divided by } 2 = 1$).

7. Conclusion: This resulting number is the valence of the metal. Therefore, the name of the compound is Copper (I) Carbonate.