Surface tension is the property of the surface of a liquid that allows it to resist an external force. Due to the cohesive nature of the water molecules. Some examples of surface tension is walking on water and floating a needle.
The surface tension of water breaks when you add dish soap. The paperclip could float in regular water without trouble, but when soap is added it breaks the surface tension and causes the paperclip to sink. Because the soap caused the water skin to break it caused the paperclip to sink.