diff --git a/index.html b/index.html
index 12a5549..0acfb66 100644
--- a/index.html
+++ b/index.html
@@ -2101,19 +2101,48 @@ function collideTwoElements(elementA, elementB, compatible=true){ // dropping b
 	dir.subVectors( a, b ).normalize()
 	if (!compatible){
 		elementB.object3D.position.add( dir.multiplyScalar(-1)) // repulsive
+		// should be clamped, e.g maximum .1 unit bouncing
 	} else {
 		elementB.object3D.position.copy( a )
 		vol.setFromObject( elA.object3D )
-		elementB.object3D.position.x += (vol.max.x - vol.min.x) // snapping equivalent
+		let width = (vol.max.x - vol.min.x)
+		// should check first is unoccopied, otherwise move further until empty
+		elementB.object3D.position.x += width // snapping equivalent
 		// then can also test for larger structures
 			// e.g H2O chain "../content/WaterBottle.glb" // by sirkitree (CC-BY)
+			// can rely on getClosestTargetElement() with the before/after position
+				// by default .05 threshold
+		let presentAtoms = {H:0, O:0, C:0}
+		presentAtoms[ elementA.getAttribute("value") ]++
+		presentAtoms[ elementB.getAttribute("value") ]++
+		let before = a.clone()
+		before.x -= width
+		let after = a.clone()
+		after.x += width*2 // one of them is a duplicate... might be already positioned correctly before?
+		presentAtoms[ getClosestTargetElement( before ).getAttribute("value") ]++
+		presentAtoms[ getClosestTargetElement( after ).getAttribute("value") ]++
+		const compoundChemistryExamples = [ {atoms:{H:2, O:1, C:0},name:"water",url_model:"../content/WaterBottle.glb"} ]
+		console.log( presentAtoms, compoundChemistryExamples[0] )
+		compoundChemistryExamples.map( x => {
+			console.log("comparing", x.atoms, presentAtoms)
+			if (
+
+				Object.keys(x.atoms).map( k => x.atoms[k] <= presentAtoms[k] ) // simplified, should be exact match
+					.reduce( (a,b) => (a&&b) )
+			){
+				console.log( x.name, "found", x.url_model,"to display")
+				addGltfFromURLAsTarget( x.url_model, .1 )
+			}
+		})
 	}
 }
 /* testing
-elA = addBlockCodeExample('O', '-0.2 1.4 -0.2')
-elB = addBlockCodeExample('H') // need few milliseconds to create before testing, so no copy/paste
-collideTwoElements(elA, elB)
-collideTwoElements(elA, elB, false)
+
+elA = addBlockCodeExample('O', '-0.2 1.4 -0.2'); elB = addBlockCodeExample('H'); elC = addBlockCodeExample('H', '0.2 1.4 -0.2')
+collideTwoElements(elA, elB); collideTwoElements(elB, elC);
+
+add a new component to see if a group has been modified
+	means creating first an entity to receive that component and as children the other entities
 */
 
 function addBlockCodeExample(text="hi", pos="0 1.4 -0.2", color="black", outlineColor="white"){