The Cation Identity Slides Case File: 001
The Cation Identity
Unmasking the variable charges of transition metals
Chemistry Unit 4
Exhibit A: The Copper Conundrum
Compound Alpha
A fine reddish powder
Cu₂O
Compound Beta
A gritty black powder
CuO
"Both substances contain ONLY copper and oxygen. If they are the same elements, why are they different?"
The Evidence: Ratio Analysis
What we know:
Oxygen always forms a 2- charge.
Ionic compounds must be neutral (Total Charge = 0).
If the Oxygen charge doesn't change, then the Copper charge must be different in each compound.
Compound Total Anion Charge Cation Charge? CuO 1 × (-2) = -2 +2 Cu₂O 1 × (-2) = -2 +1 (each)
The Variable Charge Rule
Unlike Group 1 or 2 metals, most Transition Metals can lose a different number of electrons depending on the situation.
Fe
Iron
+2 or +3
Cu
Copper
+1 or +2
Sn
Tin
+2 or +4
This means the name "Copper Oxide" is not enough. We need to be more specific.
Ready to play Detective?
You are about to receive a series of chemical "incident reports." Your job is to determine the charge of the metal cation in each sample.
Open Lab Notebooks
Review Oxidation Rules
Charge Detective Worksheet Case File: Charge Detective
Topic: Determining Unknown Cation Charges
Detective:
Date:
The Assignment
In ionic compounds, the Total Positive Charge must exactly cancel out the Total Negative Charge. Use the known charge of the anion (non-metal) to determine the mystery charge of the multivalent metal cation.
Section 1: The Known Quantities
Fill in the standard charges for these common anions. You will need these to solve the cases below.
Oxide (O)
______
Chloride (Cl)
______
Sulfide (S)
______
Nitride (N)
______
Section 2: Evidence Analysis
For each compound, calculate the charge of the metal cation. Show your work steps below each formula.
Compound FeCl₃
Show your calculation:
Cation Charge:
Compound SnO₂
Show your calculation:
Cation Charge:
Compound Cu₂S
Show your calculation:
Cation Charge:
Compound Pb₃N₄
Show your calculation:
Cation Charge:
Detective's Summary:
Why is it impossible to know the charge of the metal by just looking at its symbol (e.g., "Fe") on the periodic table?
System Update Slides System Update v. IUPAC
THE STOCK SYSTEM
"Because 'Iron Oxide' is no longer precise enough for our needs."
NOMENCLATURE PROTOCOL 2.0
The Problem with the Past
Chemists used to use Latin-based names to distinguish charges:
IRON (II) Ferrous
IRON (III) Ferric
COPPER (I) Cuprous
COPPER (II) Cupric
Why it failed:
Confusing (which one is "ous" and which is "ic"?)
Doesn't work for elements with 3+ charges
Inconsistent across different languages
The Stock System Rule
Metal Name + (Roman Numeral) + Anion Name -ide
Charge: +1
(I)
Charge: +2
(II)
Charge: +3
(III)
Charge: +4
(IV)
The Roman numeral ALWAYS represents the charge of the cation, not the number of atoms.
Nomenclature in Action
Compound: FeO
1. Charge of Oxygen = -2
2. Charge of Iron must be +2
Iron (II) oxide
Compound: Fe₂O₃
1. Total negative charge = -6 (3 x -2)
2. Charge of each Iron must be +3
Iron (III) oxide
Crucial Tip
If the metal is NOT a transition metal (like Sodium or Aluminum), we NEVER use Roman numerals. They are only for elements that vary!
System Upgrade: Protocol Workshop
Time to apply the Stock system to modernize our lab inventory records.
Start Workshop
Rules Reference
Nomenclature Upgrade Worksheet Nomenclature Upgrade
Task: Stock System Calibration
STUDENT ID: ____________________
DATE: 2026-01-17
01
Modernizing Archaic Records
Legacy lab records use outdated Latin-based naming conventions. Translate these "Old World" names into the modern **IUPAC Stock System**.
Ferrous Chloride
→
FeCl₂
STOCK NAME: Iron (II) chloride
Stannous Oxide
→
SnO
STOCK NAME:
Stannic Oxide
→
SnO₂
STOCK NAME:
Plumbous Sulfide
→
PbS
STOCK NAME:
02
System Calibration: Formula to Name
Formula Cation Calculation IUPAC Stock Name CrO₃ Example: 3(-2) = -6, so Cr = +6 Chromium (VI) oxide Fe₂S₃ Cu₃P MnCl₄ AuN
SECURITY CHECK: The Type I Trap
The Stock system is ONLY for metals with multiple personalities. Identify which of these names are INCORRECTLY written with Roman numerals.
Sodium (I) chloride
Cobalt (II) sulfide
Aluminum (III) oxide
Tin (IV) fluoride
Formula Blueprint Slides Nomenclature Inversion
The Formula Blueprint
Deconstructing names to build precise chemical structures.
Construction Mode
The Translation Key
Iron (III) oxide
Fe3+
1
Identify the Metal
Write the symbol first.
2
Extract the Charge
The Roman numeral IS the charge of the metal.
3
Identify the Anion
Determine the non-metal's group charge.
Warning: The Subscript Trap
Common Error:
Copper (II) chloride
Cu2Cl
"The student saw a 2 and put it in the subscript. This is WRONG."
Correct Approach:
Copper (II) Charge: Cu2+
Chloride Charge: Cl1-
CuCl2
The Balance of Power
Lead (IV) Sulfide
Cation: Pb4+
Anion: S2-
Simplified Formula
PbS2
Gold (III) Oxide
Cation: Au3+
Anion: O2-
Neutral Formula
Au2O3
Mn (VII) Oxide
Cation: Mn7+
Anion: O2-
Complex Formula
Mn2O7
Detecting Formula Fraud
An 'AI' has been attempting to write chemical formulas for our lab, but it keeps confusing Roman numerals with subscripts.
Begin Error Detection Mission
Formula Fraud Detector Worksheet Formula Fraud Detector
Security Protocol: 404-NOMEN-ERROR
Inspector Name:
High Priority
System Incident Report
A prototype AI lab-assistant named CHEM-BOT v1.0 has generated several formulas based on chemical names. However, our sensors indicate a 95% error rate. Your task is to audit the output, identify the specific mistake, and write the corrected formula.
Audit Log: AI Output Review
Chemical Name AI's Formula The Logic Error Correct Formula Iron (III) oxide Fe₃O Confused (III) with the subscript for Iron. Copper (II) chloride Cu₂Cl
|
|
| Lead (IV) sulfide | Pb₄S |
|
|
| Tin (II) nitride | Sn₂N |
|
|
Independent Calibration
Generate accurate formulas for these samples to verify your own calibration.
Manganese (IV) oxide:
Gold (III) chloride:
Mercury (II) sulfide:
Chromium (III) nitride:
Cobalt (III) phosphide:
Titanium (IV) fluoride:
Technician's Debrief:
Explain in your own words why a student might think the formula for Nickel (II) bromide is Ni₂Br, and why that logic is scientifically flawed.
The Transition Metal Mystery Lab Handout Lab Protocol: TM-22-EX
The Oxidation State Mystery
Date: ________
Station: ________
Investigation Goal
You are provided with three unknown solutions, each containing a multivalent metal ion (Iron or Copper). By reacting these with Sodium Hydroxide (NaOH), you will observe unique precipitate colors that reveal the identity and oxidation state of the metal cation.
Safety Gear
NaOH is corrosive. Wear eye protection.
The Evidence Legend
Copper (II)
Blue Precipitate
Copper (I)
Yellow/Orange Ppt
Iron (II)
Dirty Green Ppt
Iron (III)
Rusty Red/Brown Ppt
Observation Log
Sample Initial Appearance Precipitate Color Identity of Cation A B C
Data Analysis & Synthesis
1. Write the full IUPAC Name and chemical formula for the compound formed in Sample A.
Name:
Formula:
2. Explain how the Roman numeral in the name for Sample B helped you determine its formula.
3. Reflection: If you found a rusty-colored precipitate in a sample known to contain iron, which oxidation state of iron is present? Why is it "unstable" for this metal to only have one charge?
Stamp
Experimental Data verified by Lead Laboratory Technician
Technician Signature
Codebreaker Challenge Slides System Initializing...
CODEBREAKER
Multivalent Nomenclature Challenge
Speed
Decode formulas in under 15 seconds.
Precision
One wrong numeral ends the streak.
The Code
Correct numerals reveal the vault key.
Mission Briefing
1
You will be presented with 10 Chemical Compounds.
2
Identify the Roman Numeral for each metal.
3
Convert the Roman numerals to digits (e.g., III = 3).
The Digital Lock
The sum of all 10 digits is your Master Code. Enter the master code into the interface to decrypt the secret message.
?
?
?
Training Pulse
Sample Formula
MnO₂
Step 1
Oxygen = -2 x 2 = -4
Step 2
Manganese must be +4
Digit
4
Rapid Fire Mode
When the formula appears, your team has 10 seconds to write the digit on your whiteboard.
READY?
Decrypt the Vault
Total the digits from all 10 rounds. If your sum matches the terminal input, you've mastered the Multivalent Code.
Master Code Sum:
--
Codebreaker Challenge Worksheet Codebreaker Terminal v4.0
SYSTEM STATUS: ENCRYPTED
DECRYPTION PROTOCOL
The following 10 data packets contain encrypted chemical signatures. To decrypt the master vault, you must extract the magnitude of the metal's charge from each formula. Sum these digits to calculate the FINAL MASTER KEY.
PACKET_ID: 001 FORMULA
SnCl₄
Charge Digit:
PACKET_ID: 002 FORMULA
Fe₂O₃
Charge Digit:
PACKET_ID: 003 FORMULA
CuS
Charge Digit:
PACKET_ID: 004 FORMULA
PbO₂
Charge Digit:
PACKET_ID: 005 FORMULA
AuCl₃
Charge Digit:
PACKET_ID: 006 FORMULA
Cr₂S₃
Charge Digit:
PACKET_ID: 007 FORMULA
MnN
Charge Digit:
PACKET_ID: 008 FORMULA
NiBr₂
Charge Digit:
PACKET_ID: 009 FORMULA
Hg₂O
Charge Digit:
PACKET_ID: 010 FORMULA
TiF₄
Charge Digit:
CALCULATE MASTER KEY
Sum of Digits
=
Master Code