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than one might expect of emptiness (fluctuations of energy in this 'emptiness', called vacuum fluctuations, explain spontaneous radioactive decay).

The larger world, stepping up from the atomic scale, is able to exist as a single atom is electrically neutral, and so they don't repel each other. This allows atoms to pass close to each other at least to an extent and chemistry is, in a sense, the study of what happens when atoms pass close to each other. When two atoms come close together, their outermost electrons repel each other, but many other things can happen which together explain the vibrant world we live in.

One of the most important quantities in the interaction of atoms is electronegativity, which isn't actually a new quantity at all it's the power of the nucleus of an atom to pull more electrons to it. The nucleus is positively charged and electrons are negatively charged, so the nucleus of one atom can pull on the electrons of another. They can even steal an electron from another atom entirely. If this happens, both atoms have an overall charge (one has lost some negative charge and so is slightly positively charged, and the other vice versa). An 'atom' with an uneven charge is called an ion, and quite understandably two ions of opposite charges attract each other. This is called an ionic bond, and holds the two atoms together quite strongly. (They don't collapse into each other, but achieve a certain distance and then their attraction balances the repulsion between nuclei.)

Electronegativity is relative, and ionic bonds only form if one atom is far more electronegative than the other. If the difference isn't as large, then the two nuclei may struggle over an electron with neither completely taking it the electron will simultaneously exist in an orbit of one atom and the orbit of another. This is called covalent bonding, and like ionic bonding holds atoms together (just nowhere near as strongly).

Ionic bonding and covalent bonding allow atoms to form into molecules, which are groups of two or more atoms held together in a fairly stable way. Water is one of the most simple molecules, and is a group of three atoms: two hydrogen atoms and one oxygen atom. More complex molecules can form, and interact due to partial charges distributed unevenly due to electronegativity.

As aforementioned, the fundamental building block of chemistry is the atom, which "work" by being delicate balances of forces the electromagnetic force and the nuclear force. If atoms could not be at all stable, they'd never be observed as they'd collapse on themselves or fall apart (this is true of many subatomic particles we never encounter normally, such as muons and pions they lack the beautiful balance of the atom and so rarely exist for long). Similarly, if atoms were too stable, molecules could never form and the universe would be a very empty-seeming place (some elements, called the noble gases, are stable like this they don't interact with anything). Thankfully for us, atoms are stable but not usually so stable that they don't interact, and so we have chemistry and the universe we know.

Learn more about this author, Svetlana Elizabeth.
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