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Facts about Atoms for Kids


The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.

  • An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.
  • Chemical atoms, which in science now carry the simple name of “atom,” are minuscule objects with diameters of a few tenths of a nanometer and tiny masses proportional to the volume implied by these dimensions.
  • Atoms can only be observed individually using special instruments such as the scanning tunneling microscope.
  • Over 99.94% of an atom’s mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass.
  • Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels.
  • This has led to some debate about whether the ancient philosophers, who intended to refer to fundamental individual objects with their concept of “atoms,” were referring to modern chemical atoms, or something more like indivisible subatomic particles such as leptons or quarks, or even some more fundamental particle that has yet to be discovered.
  • While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table.
  • J.J. Thomson created a technique for separating atom types through his work on ionized gases, which subsequently led to the discovery of stable isotopes.
  • Chemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons.
  • When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split based on the direction of an atom’s angular momentum, or spin.
  • The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom’s mass to its charge.
  • Thus every proton in the nucleus must occupy a different state, with its own energy level, and the same rule applies to all of the neutrons.
  • For atoms with low atomic numbers, a nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match.
  • However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which modifies this trend.
  • About 339 nuclides occur naturally on Earth, of which 254 (about 75%) have not been observed to decay, and are referred to as “stable isotopes”.
  • The lowest energy state of a bound electron is called the ground state, while an electron transition to a higher level results in an excited state.
  • For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts.