![]() ![]() Beneath the molecule is the label, “B r radius equals 228 p m divided by 2 equals 114 pm. The distance between the radii is 228 p m. Beneath the molecule is the label, “C l radius equals 198 p m divided by 2 equals 99 pm.” The third diatomic molecule is in red. The Periodic Table of Elements categorizes like elements together. Therefore, the nucleus has less of a pull on the outer electrons and the atomic radii are larger. The distance between the radii is 198 p m. In a group, the valence electrons keep the same effective nuclear charge, but now the orbitals are farther from the nucleus. The second diatomic molecule is in a darker shade of green. Beneath the molecule is the label, “F radius equals 128 p m divided by 2 equals 64 p m.” The next three models are similarly used to show the atomic radii of additional atoms. The distance between the centers of the two atoms is indicated above the diagram with a double headed arrow labeled, “128 p m.” The endpoints of this arrow connect to line segments that extend to the atomic radii below. Elements within a period display periodic table trends, moving from left to right, involving atomic and ionic radius. Because much of the chemistry of an element is influenced by valence electrons, we would expect that these elements would have similar chemistryand they do. ![]() Two spheres are pushed very tightly together. For example, elements in group 1 have 1 valence electron, elements in groups 3-12 have a variable number of valence electrons, and elements in group 17 have 7 valence electrons. They all have a similar electron configuration in their valence shells: a single s electron. The first model, in light green, is used to find the F atom radius. ![]() In figure a, 4 diatomic molecules are shown to illustrate the method of determining the atomic radius of an atom. The general trend is that radii increase down a group and decrease across a period. (b) Covalent radii of the elements are shown to scale. The atomic radius for the halogens increases down the group as n increases. \): (a) The radius of an atom is defined as one-half the distance between the nuclei in a molecule consisting of two identical atoms joined by a covalent bond. ![]()
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