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The single most important characteristic of an atom is its atomic number (usually denoted by the letter Z), which is defined as the number of units of positive charge (protons) in the nucleus. For example, if an atom has a Z of 6, it is carbon , while a Z of 92 corresponds to uranium .
Atomic model, in physics, a model used to describe the structure and makeup of an atom. Atomic models have gone through many changes over time, evolving as necessary to fit experimental data. For a more in-depth discussion of the history of atomic models, see atom: development of atomic theory.
The classical “planetary” model of an atom. The protons and neutrons in the nucleus are circled by electrons in “orbit” around the nucleus. The number of protons determines which element is represented, the number of electrons determines its charge, and the number of neutrons determines which isotope of the element is represented. (more ...
Atom - Development, Theory, Structure: The concept of the atom that Western scientists accepted in broad outline from the 1600s until about 1900 originated with Greek philosophers in the 5th century bce.
Thomson atomic model, earliest theoretical description of the inner structure of atoms, proposed about 1900 by William Thomson (Lord Kelvin) and strongly supported by Sir Joseph John Thomson, who had discovered (1897) the electron, a negatively charged part of every atom.
Bohr model, description of the structure of atoms proposed in 1913 by the Danish physicist Niels Bohr. The Bohr model of the atom, a radical departure from earlier, classical descriptions, was the first that incorporated quantum theory and was the predecessor of wholly quantum-mechanical models.
Atomic theory, ancient philosophical speculation that all things can be accounted for by innumerable combinations of hard, small, indivisible particles (called atoms) of various sizes but of the same basic material; or the modern scientific theory of matter according to which the chemical elements.
The periodic table is a tabular array of the chemical elements organized by atomic number, from the element with the lowest atomic number, hydrogen, to the element with the highest atomic number, oganesson.
The Rutherford atomic model relied on classical physics. The , relying on quantum mechanics, built upon the Rutherford model to explain the orbits of electrons. Read about the Thomson atomic model—the earliest model of atomic structure—and how Ernest Rutherford’s gold-foil experiment disproved it.
The modern version of atomic structure begins with Ernest Rutherford’s recognition that an atom consists of a single, central, massive, positively charged nucleus surrounded by electrons. The number of protons in the nucleus is the atomic number, Z, of the element.