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When comparing the properties of the chemical elements, recurring ('periodic') trends are apparent. This led to the creation of the periodic table as a useful way to display the elements and rationalize their behavior. When laid out in tabular form, many trends in properties can be observed to increase or decrease as one progresses along a row or column. These period trends can be explained by theories of atomic structure. The elements are laid out in order of increasing atomic number, which represents increasing positive charge in the atomic nucleus. Negative electrons are arranged in orbitals around the nucleus; recurring properties are due to recurring configurations of these electrons. These periodic trends are distributed among 3 different properties namely, physical properties, chemical properties and on the basis of chemical reactivity. In chemical properties, it is classified on the basis of two i.e.periodicity of valence or oxidation states, anomalous properties of second period elements. In this article the periodic trends with respect to their physical properties are briefly discussed. == Atomic radius == (詳細はatomic nucleus to the outermost stable electron orbital in an atom that is at equilibrium. The atomic radii tend to decrease across a period from left to right. The atomic radius usually increases while going down a group due to the addition of a new energy level (shell). However, atomic radii tend to increase diagonally, since the number of electrons has a larger effect than the sizeable nucleus. For example, lithium (145 picometer) has a smaller atomic radius than magnesium (150 picometer). Atomic radius can be further specified as: *Covalent radius: half the distance between two atoms of a diatomic compound, singly bonded. *Van der Waals radius: half the distance between the nuclei of atoms of different molecules in a lattice of covalent molecules. *Metallic radius: half the distance between two adjacent nuclei of atoms in a metallic lattice. *Ionic radius: half the distance between two nuclei 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Periodic trends」の詳細全文を読む スポンサード リンク
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