diff --git a/js/charges-and-fields/model/ChargedParticle.js b/js/charges-and-fields/model/ChargedParticle.js
index e8022a4f..f1d8768c 100644
--- a/js/charges-and-fields/model/ChargedParticle.js
+++ b/js/charges-and-fields/model/ChargedParticle.js
@@ -7,9 +7,11 @@
  */
 
 import merge from '../../../../phet-core/js/merge.js';
+import PhetioObject from '../../../../tandem/js/PhetioObject.js';
 import Tandem from '../../../../tandem/js/Tandem.js';
+import NumberIO from '../../../../tandem/js/types/NumberIO.js';
+import VoidIO from '../../../../tandem/js/types/VoidIO.js';
 import chargesAndFields from '../../chargesAndFields.js';
-import ChargedParticleIO from './ChargedParticleIO.js';
 import ModelElement from './ModelElement.js';
 
 class ChargedParticle extends ModelElement {
@@ -25,7 +27,7 @@ class ChargedParticle extends ModelElement {
 
       // {Tandem}
       tandem: Tandem.REQUIRED,
-      phetioType: ChargedParticleIO,
+      phetioType: ChargedParticle.ChargedParticleIO,
       phetioDynamicElement: true
     }, options );
     super( initialPosition, options );
@@ -34,7 +36,51 @@ class ChargedParticle extends ModelElement {
     // @public (read-only) {number} - a charge of one corresponds to one nano Coulomb
     this.charge = charge;
   }
+
+  // @public
+  applyState( stateObject ) {
+    super.applyState( stateObject );
+    this.charge = stateObject.charge;
+  }
+
+  /**
+   * @public
+   * @returns {Object}
+   * @override
+   */
+  toStateObject() {
+    const parentStateObject = super.toStateObject();
+    parentStateObject.charge = this.charge;
+    return parentStateObject;
+  }
+
+  /**
+   * @override
+   * @param {Object} stateObject - see ChargedParticleIO.toStateObject
+   * @returns {Array.<*>}
+   * @public
+   */
+  static stateToArgsForConstructor( stateObject ) {
+    assert && assert( stateObject.charge === 1 || stateObject.charge === -1 );
+    // Put charge first for the chargedParticleGroup create function api.
+    return [ stateObject.charge ].concat( ModelElement.ModelElementIO.stateToArgsForConstructor( stateObject ) );
+  }
 }
 
+ChargedParticle.ChargedParticleIO = PhetioObject.createIOType( ChargedParticle, 'ChargedParticleIO', ModelElement.ModelElementIO, {
+  documentation: 'A Charged Particle',
+  methods: {
+    setCharge: {
+      returnType: VoidIO,
+      parameterTypes: [ NumberIO ],
+      implementation: function( value ) {
+        this.phetioObject.charge = value.charge;
+      },
+      documentation: 'Set charge (in units of e)',
+      invocableForReadOnlyElements: false
+    }
+  }
+} );
+
 chargesAndFields.register( 'ChargedParticle', ChargedParticle );
 export default ChargedParticle;
\ No newline at end of file
diff --git a/js/charges-and-fields/model/ChargedParticleIO.js b/js/charges-and-fields/model/ChargedParticleIO.js
deleted file mode 100644
index 20f3d47a..00000000
--- a/js/charges-and-fields/model/ChargedParticleIO.js
+++ /dev/null
@@ -1,62 +0,0 @@
-// Copyright 2017-2020, University of Colorado Boulder
-
-/**
- * IO type for ChargedParticle
- *
- * @author Sam Reid (PhET Interactive Simulations)
- * @author Andrew Adare (PhET Interactive Simulations)
- */
-
-import validate from '../../../../axon/js/validate.js';
-import NumberIO from '../../../../tandem/js/types/NumberIO.js';
-import ObjectIO from '../../../../tandem/js/types/ObjectIO.js';
-import VoidIO from '../../../../tandem/js/types/VoidIO.js';
-import chargesAndFields from '../../chargesAndFields.js';
-import ModelElementIO from './ModelElementIO.js';
-
-class ChargedParticleIO extends ModelElementIO {
-
-  /**
-   * @public
-   * @param {ChargedParticle} chargedParticle
-   * @returns {Object}
-   * @override
-   */
-  static toStateObject( chargedParticle ) {
-    validate( chargedParticle, this.validator );
-    const parentStateObject = ModelElementIO.toStateObject( chargedParticle );
-    parentStateObject.charge = chargedParticle.charge;
-    return parentStateObject;
-  }
-
-  /**
-   * @override
-   * @param {Object} stateObject - see ChargedParticleIO.toStateObject
-   * @returns {Array.<*>}
-   * @public
-   */
-  static stateToArgsForConstructor( stateObject ) {
-
-    // Put charge first for the chargedParticleGroup create function api.
-    return [ stateObject.charge ].concat( ModelElementIO.stateToArgsForConstructor( stateObject ) );
-  }
-}
-
-ChargedParticleIO.methods = {
-  setCharge: {
-    returnType: VoidIO,
-    parameterTypes: [ NumberIO ],
-    implementation: function( value ) {
-      this.phetioObject.charge = value.charge;
-    },
-    documentation: 'Set charge (in units of e)',
-    invocableForReadOnlyElements: false
-  }
-};
-ChargedParticleIO.documentation = 'A Charged Particle';
-ChargedParticleIO.validator = { isValidValue: v => v instanceof phet.chargesAndFields.ChargedParticle };
-ChargedParticleIO.typeName = 'ChargedParticleIO';
-ObjectIO.validateSubtype( ChargedParticleIO );
-
-chargesAndFields.register( 'ChargedParticleIO', ChargedParticleIO );
-export default ChargedParticleIO;
\ No newline at end of file
diff --git a/js/charges-and-fields/model/ChargesAndFieldsModel.js b/js/charges-and-fields/model/ChargesAndFieldsModel.js
index a843de6c..2c7dde9a 100644
--- a/js/charges-and-fields/model/ChargesAndFieldsModel.js
+++ b/js/charges-and-fields/model/ChargesAndFieldsModel.js
@@ -21,13 +21,12 @@ import Tandem from '../../../../tandem/js/Tandem.js';
 import chargesAndFields from '../../chargesAndFields.js';
 import ChargesAndFieldsConstants from '../ChargesAndFieldsConstants.js';
 import ChargedParticle from './ChargedParticle.js';
-import ChargedParticleIO from './ChargedParticleIO.js';
 import ElectricFieldSensor from './ElectricFieldSensor.js';
 import ElectricPotentialLine from './ElectricPotentialLine.js';
 import ElectricPotentialLineIO from './ElectricPotentialLineIO.js';
 import ElectricPotentialSensor from './ElectricPotentialSensor.js';
 import MeasuringTape from './MeasuringTape.js';
-import ModelElementIO from './ModelElementIO.js';
+import ModelElement from './ModelElement.js';
 
 // constants
 const GRID_MINOR_SPACING = ChargesAndFieldsConstants.GRID_MAJOR_SPACING / ChargesAndFieldsConstants.MINOR_GRIDLINES_PER_MAJOR_GRIDLINE;
@@ -136,7 +135,7 @@ class ChargesAndFieldsModel extends PhetioObject {
       return chargedParticle;
     }, [ 1, Vector2.ZERO ], {
       tandem: tandem.createTandem( 'chargedParticleGroup' ),
-      phetioType: PhetioGroupIO( ChargedParticleIO ),
+      phetioType: PhetioGroupIO( ChargedParticle.ChargedParticleIO ),
       phetioDynamicElementName: 'particle'
     } );
     const chargedParticleGroup = this.chargedParticleGroup;
@@ -145,7 +144,7 @@ class ChargesAndFieldsModel extends PhetioObject {
     // This is the relevant array to calculate the electric field, and electric potential
     // @public {ObservableArray.<ChargedParticle>}
     this.activeChargedParticles = new ObservableArray( {
-      phetioType: PropertyIO( ChargedParticleIO )
+      phetioType: PropertyIO( ChargedParticle.ChargedParticleIO )
     } );
 
     // @public {PhetioGroup.<ElectricFieldSensor>} Observable group of electric field sensors
@@ -155,7 +154,7 @@ class ChargesAndFieldsModel extends PhetioObject {
       return sensor;
     }, [ Vector2.ZERO ], {
       tandem: tandem.createTandem( 'electricFieldSensorGroup' ),
-      phetioType: PhetioGroupIO( ModelElementIO )
+      phetioType: PhetioGroupIO( ModelElement.ModelElementIO )
     } ); // {ObservableArray.<ElectricFieldSensor>}
     const electricFieldSensorGroup = this.electricFieldSensorGroup;
 
diff --git a/js/charges-and-fields/model/ElectricPotentialLineIO.js b/js/charges-and-fields/model/ElectricPotentialLineIO.js
index e434b7e2..b7a80bb6 100644
--- a/js/charges-and-fields/model/ElectricPotentialLineIO.js
+++ b/js/charges-and-fields/model/ElectricPotentialLineIO.js
@@ -10,9 +10,9 @@ import validate from '../../../../axon/js/validate.js';
 import Vector2IO from '../../../../dot/js/Vector2IO.js';
 import ObjectIO from '../../../../tandem/js/types/ObjectIO.js';
 import chargesAndFields from '../../chargesAndFields.js';
-import ModelElementIO from './ModelElementIO.js';
+import ModelElement from './ModelElement.js';
 
-class ElectricPotentialLineIO extends ModelElementIO {
+class ElectricPotentialLineIO extends ModelElement.ModelElementIO {
 
   /**
    * @public
diff --git a/js/charges-and-fields/model/ModelElement.js b/js/charges-and-fields/model/ModelElement.js
index 0c386d01..2e702fd6 100644
--- a/js/charges-and-fields/model/ModelElement.js
+++ b/js/charges-and-fields/model/ModelElement.js
@@ -9,12 +9,17 @@
 import BooleanProperty from '../../../../axon/js/BooleanProperty.js';
 import Emitter from '../../../../axon/js/Emitter.js';
 import Vector2 from '../../../../dot/js/Vector2.js';
+import Vector2IO from '../../../../dot/js/Vector2IO.js';
 import Vector2Property from '../../../../dot/js/Vector2Property.js';
 import merge from '../../../../phet-core/js/merge.js';
 import PhetioObject from '../../../../tandem/js/PhetioObject.js';
+import NullableIO from '../../../../tandem/js/types/NullableIO.js';
+import ObjectIO from '../../../../tandem/js/types/ObjectIO.js';
 import chargesAndFields from '../../chargesAndFields.js';
 import ChargesAndFieldsConstants from '../ChargesAndFieldsConstants.js';
-import ModelElementIO from './ModelElementIO.js';
+
+// constants
+const NullableIOVector2IO = NullableIO( Vector2IO );
 
 class ModelElement extends PhetioObject {
 
@@ -26,7 +31,7 @@ class ModelElement extends PhetioObject {
 
     options = merge( {
 
-      phetioType: ModelElementIO
+      phetioType: ModelElement.ModelElementIO
     }, options );
     super( options );
 
@@ -119,7 +124,48 @@ class ModelElement extends PhetioObject {
 
     this.animationTween.start( phet.joist.elapsedTime );
   }
+
+  /**
+   * @public
+   * @returns {Object}
+   * @override
+   */
+  toStateObject() {
+    return {
+      initialPosition: NullableIOVector2IO.toStateObject( this.initialPosition )
+    };
+  }
+
+  // @private
+  static fromStateObject( stateObject ) {
+    return {
+      initialPosition: NullableIOVector2IO.fromStateObject( stateObject.initialPosition )
+    };
+  }
+
+  /**
+   * @param {Object} stateObject
+   * @public
+   */
+  applyState( stateObject ) {
+    const s = ModelElement.fromStateObject( stateObject );
+    this.initialPosition = s.initialPosition;
+  }
+
+  /**
+   * @public
+   * @override
+   * @param {Object} stateObject
+   * @returns {Array.<*>}
+   */
+  static stateToArgsForConstructor( stateObject ) {
+    return [ NullableIOVector2IO.fromStateObject( stateObject.initialPosition ) ];
+  }
 }
 
+ModelElement.ModelElementIO = PhetioObject.createIOType( ModelElement, 'ModelElementIO', ObjectIO, {
+  documentation: 'A Model Element'
+} );
+
 chargesAndFields.register( 'ModelElement', ModelElement );
 export default ModelElement;
\ No newline at end of file
diff --git a/js/charges-and-fields/model/ModelElementIO.js b/js/charges-and-fields/model/ModelElementIO.js
deleted file mode 100644
index abaa7aee..00000000
--- a/js/charges-and-fields/model/ModelElementIO.js
+++ /dev/null
@@ -1,50 +0,0 @@
-// Copyright 2017-2020, University of Colorado Boulder
-
-/**
- * IO type for ModelElement
- *
- * @author Sam Reid (PhET Interactive Simulations)
- * @author Andrew Adare (PhET Interactive Simulations)
- */
-
-import validate from '../../../../axon/js/validate.js';
-import Vector2IO from '../../../../dot/js/Vector2IO.js';
-import NullableIO from '../../../../tandem/js/types/NullableIO.js';
-import ObjectIO from '../../../../tandem/js/types/ObjectIO.js';
-import chargesAndFields from '../../chargesAndFields.js';
-
-const NullableIOVector2IO = NullableIO( Vector2IO );
-
-class ModelElementIO extends ObjectIO {
-
-  /**
-   * @public
-   * @param {ModelElement} modelElement
-   * @returns {Object}
-   * @override
-   */
-  static toStateObject( modelElement ) {
-    validate( modelElement, this.validator );
-    return {
-      initialPosition: NullableIOVector2IO.toStateObject( modelElement.initialPosition )
-    };
-  }
-
-  /**
-   * @public
-   * @override
-   * @param {Object} stateObject - see ModelElementIO.toStateObject
-   * @returns {Array.<*>}
-   */
-  static stateToArgsForConstructor( stateObject ) {
-    return [ NullableIOVector2IO.fromStateObject( stateObject.initialPosition ) ];
-  }
-}
-
-ModelElementIO.validator = { isValidValue: e => e instanceof phet.chargesAndFields.ModelElement };
-ModelElementIO.documentation = 'A Model Element';
-ModelElementIO.typeName = 'ModelElementIO';
-ObjectIO.validateSubtype( ModelElementIO );
-
-chargesAndFields.register( 'ModelElementIO', ModelElementIO );
-export default ModelElementIO;
\ No newline at end of file