diff --git a/js/chart-intro/model/ChartIntroModel.ts b/js/chart-intro/model/ChartIntroModel.ts
index 390b06f..d5edd26 100644
--- a/js/chart-intro/model/ChartIntroModel.ts
+++ b/js/chart-intro/model/ChartIntroModel.ts
@@ -16,6 +16,7 @@ import BANConstants from '../../common/BANConstants.js';
 import ParticleAtom from '../../../../shred/js/model/ParticleAtom.js';
 import Property from '../../../../axon/js/Property.js';
 import NuclideChartCellModel from './NuclideChartCellModel.js';
+import DecayEquationModel from './DecayEquationModel.js';
 
 // types
 export type SelectedChartType = 'partial' | 'zoom';
@@ -41,7 +42,10 @@ class ChartIntroModel extends BANModel<ParticleNucleus> {
   public readonly particleNucleus: ParticleNucleus;
   public readonly miniParticleAtom: ParticleAtom;
   public readonly selectedNuclideChartProperty: Property<SelectedChartType>;
-  public static cellModelArray = POPULATED_CELLS.map( ( row, rowIndex ) => row.map( column => new NuclideChartCellModel( rowIndex, column ) ) );
+
+  // There's not an entry for all the neutron values, see POPULATED_CELLS
+  public static cellModelArray = POPULATED_CELLS.map( ( neutronCountList, protonCount ) => neutronCountList.map( neutronCount => new NuclideChartCellModel( protonCount, neutronCount ) ) );
+  public readonly decayEquationModel: DecayEquationModel;
 
   public constructor() {
 
@@ -56,6 +60,8 @@ class ChartIntroModel extends BANModel<ParticleNucleus> {
     this.miniParticleAtom = new ParticleAtom();
 
     this.selectedNuclideChartProperty = new Property<SelectedChartType>( 'partial' );
+
+    this.decayEquationModel = new DecayEquationModel( ChartIntroModel.cellModelArray, this.particleNucleus.protonCountProperty, this.particleNucleus.massNumberProperty );
   }
 
   /**
diff --git a/js/chart-intro/model/DecayEquationModel.ts b/js/chart-intro/model/DecayEquationModel.ts
new file mode 100644
index 0000000..f6fccaa
--- /dev/null
+++ b/js/chart-intro/model/DecayEquationModel.ts
@@ -0,0 +1,87 @@
+// Copyright 2023, University of Colorado Boulder
+
+/**
+ * Node that represents the model of a decay equation.
+ *
+ * @author Luisa Vargas
+ * @author Marla Schulz (PhET Interactive Simulations)
+ */
+
+import buildANucleus from '../../buildANucleus.js';
+import NuclideChartCellModel from './NuclideChartCellModel.js';
+import TReadOnlyProperty from '../../../../axon/js/TReadOnlyProperty.js';
+import DecayType from '../../common/view/DecayType.js';
+import NumberProperty from '../../../../axon/js/NumberProperty.js';
+import Property from '../../../../axon/js/Property.js';
+
+class DecayEquationModel {
+  private readonly initialProtonNumberProperty: TReadOnlyProperty<number>;
+  private readonly initialMassNumberProperty: TReadOnlyProperty<number>;
+  private readonly finalProtonNumberProperty: Property<number>;
+  private readonly finalMassNumberProperty: Property<number>;
+
+  public constructor( cellModelArray: NuclideChartCellModel[][], protonCountProperty: TReadOnlyProperty<number>, massNumberProperty: TReadOnlyProperty<number> ) {
+
+    this.initialProtonNumberProperty = protonCountProperty;
+    this.initialMassNumberProperty = massNumberProperty;
+
+    // TODO: if at 0 protons and 0 neutrons, or if decay type is unknown, don't show the decay equation
+    this.finalProtonNumberProperty = new NumberProperty( -1 );
+    this.finalMassNumberProperty = new NumberProperty( -1 );
+
+    this.initialMassNumberProperty.link( () => {
+      const currentCell = this.getCurrentCellModel( cellModelArray, protonCountProperty.value, massNumberProperty.value );
+      console.log( cellModelArray );
+      if ( !currentCell || !currentCell.decayType ) {
+        // TODO: for stable decay types set this, is it alright?
+        this.finalProtonNumberProperty.value = this.initialProtonNumberProperty.value;
+        this.finalMassNumberProperty.value = this.initialMassNumberProperty.value;
+        return;
+      }
+      console.log( currentCell.decayType );
+      switch( currentCell.decayType ) {
+        case DecayType.NEUTRON_EMISSION:
+          this.finalProtonNumberProperty.value = this.initialProtonNumberProperty.value;
+          this.finalMassNumberProperty.value = this.initialMassNumberProperty.value - 1;
+          break;
+        case DecayType.PROTON_EMISSION:
+          this.finalProtonNumberProperty.value = this.initialProtonNumberProperty.value - 1;
+          this.finalMassNumberProperty.value = this.initialMassNumberProperty.value - 1;
+          break;
+        case DecayType.BETA_PLUS_DECAY:
+          this.finalProtonNumberProperty.value = this.initialProtonNumberProperty.value - 1;
+          this.finalMassNumberProperty.value = this.initialMassNumberProperty.value;
+          break;
+        case DecayType.BETA_MINUS_DECAY:
+          this.finalProtonNumberProperty.value = this.initialProtonNumberProperty.value + 1;
+          this.finalMassNumberProperty.value = this.initialMassNumberProperty.value;
+          break;
+        case DecayType.ALPHA_DECAY:
+          this.finalProtonNumberProperty.value = this.initialProtonNumberProperty.value - 2;
+          this.finalMassNumberProperty.value = this.initialMassNumberProperty.value - 4;
+          break;
+        default:
+          assert && assert( false, 'No valid decay type found: ' + currentCell.decayType );
+      }
+
+    } );
+
+    this.initialMassNumberProperty.link( initialMassNumber => {
+      console.log( 'initialMassNumber = ' + initialMassNumber );
+      console.log( 'initialProtonNumber = ' + this.initialProtonNumberProperty.value );
+      console.log( 'finalMassNumber = ' + this.finalMassNumberProperty.value );
+      console.log( 'finalProtonNumber = ' + this.finalProtonNumberProperty.value );
+    } );
+
+  }
+
+  /**
+   * Return the current NuclideChartCellModel for the current proton number and mass number, if there exists one.
+   */
+  private getCurrentCellModel( cellModelArray: NuclideChartCellModel[][], protonNumber: number, massNumber: number ): NuclideChartCellModel | undefined {
+    return _.find( cellModelArray[ protonNumber ], cellModel => cellModel.neutronNumber === massNumber - protonNumber );
+  }
+}
+
+buildANucleus.register( 'DecayEquationModel', DecayEquationModel );
+export default DecayEquationModel;
\ No newline at end of file
diff --git a/js/common/view/DecayType.ts b/js/common/view/DecayType.ts
index cf93466..97ecc75 100644
--- a/js/common/view/DecayType.ts
+++ b/js/common/view/DecayType.ts
@@ -15,26 +15,32 @@ import BANColors from '../BANColors.js';
 
 class DecayType extends EnumerationValue {
 
-  public static readonly ALPHA_DECAY = new DecayType( BuildANucleusStrings.alphaDecay, BANColors.alphaColorProperty );
+  public static readonly ALPHA_DECAY = new DecayType( BuildANucleusStrings.alphaDecay, BANColors.alphaColorProperty, 4, 2, 'α' );
 
-  public static readonly BETA_MINUS_DECAY = new DecayType( BuildANucleusStrings.betaMinusDecay, BANColors.betaMinusColorProperty );
+  public static readonly BETA_MINUS_DECAY = new DecayType( BuildANucleusStrings.betaMinusDecay, BANColors.betaMinusColorProperty, 0, -1, 'β' );
 
-  public static readonly BETA_PLUS_DECAY = new DecayType( BuildANucleusStrings.betaPlusDecay, BANColors.betaPlusColorProperty );
+  public static readonly BETA_PLUS_DECAY = new DecayType( BuildANucleusStrings.betaPlusDecay, BANColors.betaPlusColorProperty, 0, 1, 'β' );
 
-  public static readonly PROTON_EMISSION = new DecayType( BuildANucleusStrings.protonEmission, BANColors.protonEmissionColorProperty );
+  public static readonly PROTON_EMISSION = new DecayType( BuildANucleusStrings.protonEmission, BANColors.protonEmissionColorProperty, 0, 1, 'e' );
 
-  public static readonly NEUTRON_EMISSION = new DecayType( BuildANucleusStrings.neutronEmission, BANColors.neutronEmissionColorProperty );
+  public static readonly NEUTRON_EMISSION = new DecayType( BuildANucleusStrings.neutronEmission, BANColors.neutronEmissionColorProperty, 1, 0, 'n' );
 
   public static readonly enumeration = new Enumeration( DecayType );
 
   public readonly label: string;
   public readonly colorProperty: ProfileColorProperty;
+  public readonly massNumber: number;
+  public readonly protonNumber: number;
+  public readonly decaySymbol: string;
 
-  public constructor( label: string, colorProperty: ProfileColorProperty ) {
+  public constructor( label: string, colorProperty: ProfileColorProperty, massNumber: number, protonNumber: number, decaySymbol: string ) {
     super();
 
     this.label = label;
     this.colorProperty = colorProperty;
+    this.massNumber = massNumber;
+    this.protonNumber = protonNumber;
+    this.decaySymbol = decaySymbol;
 
   }
 }