Atom

An atom is a fundamental unit of matter, representing the smallest component of an element that retains its chemical properties. The term "atom" originates from the Greek word "atomos," meaning "indivisible," reflecting the early belief that atoms were the quanta of matter. We now know that they are composed of subatomic and elementary particles. A mere teaspoon (5ml) of water contains approximately 5 × 10²³ atoms, which shows the minuscule size of atoms and the immense number present even in small volumes of matter.

The diameters of normal atoms are in the picometre scale (10⁻¹² m) with a density of 10¹² kg/m³. Strange and degenerate compressed atoms found in neutron stars are in the 10¹⁷ kg/m³ density range. Magmatter atoms are billions of times smaller in the attometre scale (10⁻¹⁸ m) with a density of 10¹⁸ kg/m³. The super-atom, denser than magmatter, at the start of the Big Bang is the cosmon.

History

• Ancient Philosophy: The idea of indivisible particles dates back to ancient Greece, with philosophers like Democritus proposing that all matter is composed of tiny, uncuttable units called atoms. ​
• 19th Century: John Dalton formulated the modern atomic theory, suggesting that each element consists of unique atoms and that chemical reactions involve the rearrangement of these atoms. ​
• 20th Century: Discoveries by scientists such as J.J. Thomson, Ernest Rutherford, and Niels Bohr revealed the internal structure of the atom, including the existence of subatomic particles and the organization of electrons in shells around the nucleus.

Structure

• Nucleus: At the center of the atom lies the nucleus (more than 99.9994% of an atom's mass), which contains:
  • Protons: Positively charged particles.
  • Neutrons: Neutral particles with no electric charge.
• Electrons: Negatively charged particles that move around the nucleus, creating an electron cloud. The exact position of electrons cannot be determined precisely due to their wave-like behavior; instead, they are found in regions called orbitals. Electrons generate energy by moving between atoms, creating an electric current.
• Even though the mass itself is condensed in a tiny nucleus, an atom is over 99.9% empty space. Its "solidness" is just the electromagnetic force repelling electron fields.

The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force.

Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals.

Splitting the atom led to nuclear fission and the atomic bomb, and combining nuclei led to nuclear fusion and is the basis of star engines.