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The <b>atomic radius</b> of an atom refers to the distance between an atom's nucleus and its valence electrons *Moving from left to right across a period, the atomic radius decreases **The nucleus of the atom gains protons moving from left to right, increasing the positive charge of the nucleus and increasing the attractive force of the nucleus upon the electrons *The atomic radius increases moving down a group **Once again protons are added moving down a group, but so are new energy shells of electrons. The new energy shells provide shielding, allowing the valence electrons to experience only a minimal amount of the protons' positive charge The <b>ionic radius</b> is the effective distance from the nucleus of the ion to its outer shell of electrons *When one or more electrons is added to an atom, the radius increases **This/these extra electrons increase the forces of repulsion between the electrons, pushing them apart *When one or more electrons is removed from an atom, the radius decreases **This is because there are less electrons thus less repulsive forces, so the protons are able to attract the remaining electrons closer to the nucleus *Within a group of elements, the ionic radius generally decreases like the atomic radius *In a period, however, there is no clear pattern http://www.chem.uidaho.edu/~honors/graphrad.jpg http://www.monroecc.edu/wusers/flanzafame/PerRadii.pdf
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