My hands stopped in midwave as I suddenly realized I was imitating my brother. The student I tutored in chemistry stared wide-eyed at me, surprised at my enthusiastic explanation of radiation. My arms, which had been swinging wildly to portray the moving electrons, stopped abruptly. I remembered when he had explained chemistry to me.

When I was young, my brother compared the pair of us to an atom. He was the large, important nucleus, circled by me, an infinitesimal electron. At the time I did not understand the meaning of the atom, but I knew the two pieces, if on a human scale, would be football fields apart.

I sidled up to my brother and interrupted his important video games. I followed him, at my electron's distance, watching from years away. He brushed away my conversation, he ignored my existence. I was devoted still. The attraction between a positive nucleus and a negative electron is one of the strongest in the physical world.

As the years passed, the distance between us decreased. We hesitantly began speaking to each other. We took long drives in the icy winters, exploring strange new roads just to have more time together. The old car murmured and groaned as we shared our expectations and fears about friends, college and the future.

He loved explaining science to me. I watched, entranced, as his hands flung themselves apart and he vigorously slammed matchbooks together to explain the universal law of gravitation. We sat under burning lamps for hours as he explained mathematics. His long-fingered hands would gesture at the frightening mass of numbers and coax out a simple answer. His video games and his homework were forgotten in the comer, while his flying hands pulled answers out of the air and slowly untangled my world.

Now he has left, and the answers are not as easy to find. Last year I learned about radioactivity, and it seemed like a postscript on the past. Some elements are naturally radioactive, meaning the atoms will split apart eventually, the nucleus and the electron will fly off in different directions. I listen to the awkward pauses on the phone, and in my mind I see him contentedly studying and working, farther and farther away. I find myself missing the stable, simple elements in the periodic table, where the electron circles the center forever.