When someone boils an egg, it does undergo a chemical change with the molecules of fluid proteins crosslinking and uncoiling to create a network. A chemical change occurs when new chemical substances form. On the molecular level, this means that the bonds that exist between atoms are either broken or created.
When boiling an egg, the proteins in the white of the egg get agitated. They essentially start to slam into each other and this results in the weak bond breaking so that the proteins no longer curl up. They start to hit into other uncurled proteins and then the formation of new chemical bonds occurs.