- Physics and biology both have "dissident" scientists who disagree with some of the key fundamentals in the science. You don't have to spend too much time in physics forums to run across people who think that all of quantum mechanics and/or relativity is wrong, and that they have a better explanation that doesn't require ideas that clash with our everyday experiences. Biologists have to deal with all the people, including scientists, who deny evolution. Fortunately, chemistry seems to be immune to "dissident" thought. I can't think of a single example where a fundamental chemical idea is challenged.
- Physics and biology have both done a better job of selling themselves to the general public than chemistry has. Physicists are able to get funding for particle accelerators that may not ever be able to produce results applicable to the "real world", and yet many in the general public are well aware of the search for the Higgs Boson. Astrophysicists are similarly able to get funding for ever larger telescopes and space telescopes. As long as they produce the occasional breathtaking picture of nebula and galaxies, the general public is happy. As for biologists, they were able to get billions for sequencing the human genome, although they at least held out the promise of "personalized medicine" and the discovery of the gene that causes disease X, Y and Z (with the soon to follow cure for these diseases). Has there ever been a large scale chemistry project, let alone one that captured the public's imagination? I can't think of any.
- Chemistry seems to more feared by the public than physics or biology is. I'll admit that this is a personal perception that might be heavily tainted by my experiences, but it seems to me that there is more chemophobia than there is fear of anything that physicists or biologist work with. Certainly there is fear of radiation and certain microbiological organisms, but these fears are limited to rather thin facets of life - nuclear power plants & weapons for physics, and food safety & infections/disease for biologists, whereas chemophobia can exist with practically everything that people touch in their lives. If a physicist is working with optics, that's o.k. If a biologist is working with fish, that's o.k. [*] If a chemist is working at all, it's with chemicals and that's bad no matter what.
[*]as long as they are not genetically modified fish. (I realize this is a small concern in the US and a bigger concern in Europe.)