Martin Leberle, Age 13, Of Cliffside Park, N.J.., for his question:
What is the lightest substance known to man?
Scientists must be very careful. About comparing the weights of different substances. You can jam pack a bundle of fluffy feathers and compress it until it becomes as heavy as cork or even wood. A pint of hot water is lighter than a pint of ice water. In ccmparing weights of different substances, we must provide the same conditions for each of our samples.
We can use guesswork to tell that a stone is heavicr than water and that water is heavier than the filmy air above it. But guesswork never gives an exact picture, and the details it omits are usually the most interesting ones. We could never guess, for example, that certain air molecules are 131 times heavier than others or that ice water is heavier than hot water.
We might guess that the lightest substance is a gas, and this guess is correct. But a gas, like other substances, expands and becomes lighter with heat. Under pressure and certain other conditions, its atoms and m01ecules can be packed densely together, and the gas beccmles heavier. So we should weigh our sample substances under normal. Prebsure at normal room temprrature.
A glass flask holding a pint of ordinary air can be weighed on a delicate scale. It weighs 14 times more than a pint flask of hydrogen gas. Oxygen gas weighs about 16 times, and neon gas about 20 times, more than hydrogen. In fact, we shall find no substance as light as hydrogen.
A trace, just a trace, of hydrogen is present in the air, and small amounts collect in mines and oil wells. It is always ready to explode and to join with other elements to form compounds. If you put a spark to a mixture of hydrogen and oxygen, you get a flash flame, and the two elements combine to form liquid water. Hydrogen unites, for example, to form the compound. Hydrochloric acid and the hydrocarbon ccmpounds in plant and animal cells.
The weights of the different elements gave science the weights of the different atoms and this led to the discovery that atoms are made of particles. Hydrogen, with one proton in its nucleus and one outer electron, is atomic number one. Helium, with two protons and two electrons, is atomic number two. The atomic weight of hydrogen is 1.0080. The atomic weight of helium, the second lightest substance, is 4.003 which is almost four times heavier than hydrogen, the lightest substance in the whole universe.
Hydrogen makes up ,just a fraction of our world, but out in space it is the most plentiful of all elements. Star material is about 75% hydrogen, and vast clouds of hydrogen hover throughout the galaxy. The terrific pressure in the heart of our sun strips off outer electrons and jam packs the hydrogen until it beccmes heavier than water. In certain dense, dwarf stars, a pint of coenpressed hydrogen may weigh 25 tons or more.