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Atomic radius measures the distance between the nucleus and outer edge of electrons. It varies depending on bonding and position on the periodic table. Helium has the smallest radius, while cesium has the largest. Covalently bonded atoms have different radii than touching atoms. Atomic radius is based on the principle that atoms are spheres, and increases along rows and down columns of the periodic table. It helps explain molecular shape and size and was used in the development of quantum theory.
Atomic radius is a measure of size for atoms of a specific element. It indicates the distance between the nucleus of an atom and the outer edge of its electrons, i.e. the distance between two atomic nuclei. An atom has no fixed structure, so its atomic radius is measured by dividing the distance between the nuclei of touching atoms in half. The radius can be different for the same atom depending on whether it is bonded or just next to another atom. Atomic size decreases further along each row of the periodic table when considering alkali metals in noble gases, and increases down columns.
An atomic radius table is structurally different from the classic periodic table of elements. Helium has the smallest radius, while hydrogen, the lightest element, is sixth from the bottom for size measurement, and cesium is the largest atom. Neutral atoms range in size from 0.3 to 3 angstroms, and atoms and ions with one electron can be measured using the Bohr radius, determined by the orbit of the lowest energy electron in the atom.
The radius of covalently bonded atoms is different from that of touching atoms. Atoms that are bonded share electrons and the radii of densely packed atoms, such as in a metallic structure, are different than if the atoms were simply next to each other. The van der Waals beam is used for atoms that are held together by weak attractions and not held together in a molecule. Adding electrons to an atom changes its atomic radius, so the ionic radius can vary depending on how many electrons orbit an ion.
Atomic radius is based on the principle that atoms are spheres. This is not exactly the case and the spherical model is only a rough representation. The idea of spherical atoms helps explain and predict how dense liquids and solids are, how atoms are arranged in crystals, and to calculate molecular shape and size. Atoms increase in radius along rows of the periodic table, but increase markedly in size between the noble gases at the end of the row, or period, and the alkali metal starting in the next row. This concept was used in the development of quantum theory and is logical in relation to the electron shell theory, which explains how many electrons can be in a particular orbit.
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