10 Greatest Ideas in the History of Science
Matter Is Made of Atoms

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‹‹ Entropy: Universe Tends Toward Disorder Symmetry Quantifies Beauty ››

Air, water, bacteria, humans, computers, the stars: all of them are made from atoms. In fact, the atoms that make up Earth (and everything on it, including us), originally came from the stars, which is why Carl Sagan famously quipped, "We are made of starstuff."

But what are atoms? Mostly empty space, actually. That means you are mostly empty space, as well. The center of each atom, called a nucleus, consists of positively-charged protons and uncharged neutrons. Surrounding this dense cluster of positivity are the negatively-charged electrons, which buzz about, rather unpredictably. Originally, it was thought that the electrons orbited the nucleus in a way that resembles the planets around the sun, the so-called "solar system model" of the atom, for which Niels Bohr is given credit. The model is overly simplistic and incorrect, but it does well enough for certain calculations, which is why it is still taught in basic chemistry classes. The model was ultimately replaced with the more complex orbital model.

All the known atoms are found on the periodic table, the centerpiece of every chemistry class. The table organizes the atoms in various ways, two of which are particularly important: First, the atoms are arranged by increasing atomic number, which represents the number of protons and defines each element. Second, each column on the table represents the number of outer shell electrons in each atom. This is important because the outer shell electrons largely determine the sorts of chemical reactions in which the atoms will participate.

Perhaps the most fascinating aspect of the periodic table is how it came about. The Russian chemist, Dmitri Mendeleev, first created the modern periodic table. But, it was missing elements. And using his table, he correctly predicted the existence of elements that had not yet been discovered.

Source: Galileo's Finger: The Ten Great Ideas of Science by Peter Atkins

Image: NASA

‹‹ Entropy: Universe Tends Toward Disorder Symmetry Quantifies Beauty ››

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