![]() Hence the radius decreases from left to right. These atomic radii are measured in picometers: The element Hydrogen (H) has an atomic radius of 37. Periodic trends, arising from the arrangement of the periodic table, provide chemists with an invaluable tool to quickly predict an element's properties. Thus, as we move across a given period the ability of the inner electrons to cancel the increasing charge of the nucleus diminishes and the outermost electron is more strongly attracted to the nucleus. Major periodic trends include: electronegativity, ionization energy, electron affinity, atomic radius, melting point, and metallic character. Likewise, an electron in a p-orbital is does a better job than a d-orbital. Remember that electrons in the s-orbital have a greater probability of being near the nucleus than a p-orbital, so the s-orbital does a better job of canceling the nuclear charge for the outermost electron than an electron in a p-orbital. The ability of an particular inner electron to cancel the charge of the nucleus for the outermost electron depends on the orbital of that inner electron. Periodic trends are specific patterns that are present in the periodic table that illustrate different aspects of a certain element, including its size and its electronic properties. Thus you might expect there to be no change in the radius of the outermost electron orbital since the increasing charge of the nucleus would be canceled by the electrons between the nucleus and the outermost electron. While the number of positively charged protons in the nucleus increases as we move from left to right the number of negatively charged electrons between the nucleus and the outer most electron also increases by the same amount. Size generally decreases across a period from left to right: To understand this trend it is first important to realize that the more strongly attracted the outermost valence electron is to the nucleus then the smaller the atom will be. Electronegativity decreases across a period and decreases down a group. In general, atomic radius decreases across a period and increases. Because of these two trends, the largest atoms are found in the lower left corner of the periodic table, and the smallest are found in the upper right corner (Figure 8.2.4 ). Atomic radius decreases across a period and increases down a group. Atomic radius is the distance from the atoms nucleus to the outer edge of the electron cloud. Size increases down a group: The increasing principle quantum number of the valence orbitals means larger orbitals and an increase in atomic size. In the periodic table, atomic radii decrease from left to right across a row and increase from top to bottom down a column. With this in mind we understand two general trends. Atomic radius decreases across a Period, from left to right. ![]() In general the size of the atom depends on how far the outermost valence electron is from the nucleus. Key Concepts Atomic radius 1 increases down a Group, from top to bottom, of the Periodic Table.
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