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Few Chemical groups and symbols

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Periodic trends of Atomic and Ionic Radii

Atomic Radius: The radius of an atom can only be found by measuring the distance between the nuclei of two touching atoms, and then halving that distance. Ionic Radius: It is the radius of an atom's ion. Although neither atoms nor ions have sharp boundaries, they are sometimes treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice . Ionic radii are typically given in units of either picometers (pm) or Angstroms (Å), with 1 Å = 100 pm. Typical values range from 30 pm (0.3 Å) to over 200 pm (2 Å). For further reading: Atomic and Ionic Radius

Electron Affinity

Electron affinity is, essentially the opposite of the ionization energy: Instead of removing an electron from the element we add an electron to the element to create an anion. M + e- ----> M- E.A. Generally, the energy that results from this process (the electron affinity) is negative or close to zero. The more negative this energy the more this process is favored. The noble gases, alkali metals and alkali earth metals have E.A. close to zero - indicating that these groups of elements do not particularly like to become anions. However, the nonmetals and especially the halogens are highly negative and thus readily become anions. A periodic trend is evident, as was the case for the ionization energy. More.. Source: www.iun.edu/

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