1.
A hydrogen atom in a cell at the end of my nose was once part of an elephant's trunk. A carbon atom in my cardiac muscle was once in the tail of a dinosaur.
Jostein Gaarder
2.
From the results so far obtained it is difficult to avoid the conclusion that the long-range atoms arising from collision of alpha particles with nitrogen are not nitrogen atoms but probably atoms of hydrogen, or atoms of mass 2. If this be the case, we must conclude that the nitrogen atom is disintegrated under the intense forces developed in a close collision with a swift alpha particle, and that the hydrogen atom which is liberated formed a constituent part of the nitrogen nucleus.
Ernest Rutherford
3.
Finally I got to carbon, and as you all know, in the case of carbon the reaction works out beautifully. One goes through six reactions, and at the end one comes back to carbon. In the process one has made four hydrogen atoms into one of helium. The theory, of course, was not made on the railway train from Washington to Ithaca ... It didn't take very long, it took about six weeks, but not even the Trans-Siberian railroad [has] taken that long for its journey.
Hans Bethe
4.
At two-tenths the speed of light, dust and atoms might not do significant damage even in a voyage of 40 years, but the faster you go, the worse it is--space begins to become abrasive. When you begin to approach the speed of light, hydrogen atoms become cosmic-ray particles, and they will fry the crew. ...So 60,000 kilometers per second may be the practical speed limit for space travel.
Isaac Asimov
5.
Organic compounds exist in which a hydrogen atom, joined to the carbon, acquires acid properties as a result of the proximity of certain functional groupings.
Victor Grignard