Atom

The Greek philosopher Democritus was the first to suggest that all things are made of atoms in 450 BC. The Greeks believed that nothing could be smaller than an atom.

The British chemist John Dalton (September 6, 1766 - July 27, 1844) proposed the existence of atoms, which he considered to be the smallest parts of matter. The idea of atoms was already known at the time, but not widely accepted. Dalton's theory of atoms was based on actual observation. Before this, ideas about atoms were based more on philosophy.

Dalton begun using symbols to represent the atoms of different elements on September 6, 1803.

Various atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy (1808).

The first widely accepted model of atomic structure is attributed to Niels Bohr. Bohr, a Danish physicist, proposed his model of the atom in 1913, building upon Ernest Rutherford's nuclear model. The Bohr model introduced the idea of quantized energy levels for electrons, with electrons orbiting the nucleus in specific, fixed orbits.

A Swedish man  was arrested in 2011 after attempting to split atoms in his kitchen, claiming that he was only doing it as a hobby.

A cesium atom in an atomic clock beats over nine billion times a second.

Hydrogen is the most common atom in the universe.

Different measurements of the size of the hydrogen atom nucleus when a muon replaces an electron is an unsolved problem in physics known as the proton radius puzzle.

The largest atom, caesium, has a diameter of 0.00000002 of an inch.

Atoms are invisible to light itself— atoms are so much smaller than the wavelength of visible light that they don’t really interact.

No one has ever seen an atom. They’re too small to be seen by a microscope and can’t be counted or weighed individually.

Every year, about 98% of the atoms in your body are replaced.

One teaspoon of water contains about three times as many atoms as the Atlantic Ocean contains teaspoons of water.

The nucleus in an atom is incredibly tiny compared with the orbits of the electrons. Tom Stoppard, the playwright said that if the nucleus is like the altar of St Paul's cathedral, an electron is like a moth in the cathedral, one moment by the altar, the next by the dome.

An atom is about 99.999% empty space, making everything in the universe mostly nothing.

If there was no space between any of its atoms, the Earth would be the size of a baseball.

If you took out all of the empty space from between and within the atoms making up each human being, the entire human race could fit into a sugar cube.

A person is made up of 7,000,000,000,000,000,000,000,000,000 (that's 7 octillion) atoms.

Every atom in your body is billions of years old.