As we move from left to right across the periods in the periodic table the number of valence electrons increases.Īcross the group, the number of valence electrons remains the same which shows that the chemical elements present in the same group have the same number of valence electrons. The valence electrons vary across the periodic table. The valence electrons are the electrons which are present in the outermost orbital of the electronic configuration. The atomic number of the chemical elements represents the number of electrons present in the atom of the element. As stated in the law, the atomic number of the chemical element is related to the physical and chemical behavior of the chemical element due to this reason the chemical element shows periodicity in their physical and chemical behavior. In the modern periodic table the chemical elements are arranged according to their atomic number which keeps increasing as we move in the periodic table. Moseley discovered the Modern Periodic law and states that the physical properties and the chemical properties of the chemical elements are the periodic function of their atomic number. The valence electrons are present in the outermost orbital of the chemical element. Therefore the distinguishing electron must occupy either the 5 s or 5 p subshell.Hint: The atomic number of the chemical element represents the number of electrons present in the atom of the chemical element. For example, iodine is a representative element in the fifth period. The value of n, the principal quantum number for the distinguishing electron, can be quickly determined by counting down from the top of the periodic table. As a general rule, in the case of the representative elements, the distinguishing electron will be in an ns or np subshell. In the third period the 3 s subshell is filling for Na and Mg, and therefore Al, Si, P, S, Cl, and Ar. Across the second period Li and Be have distinguishing electrons in the 2 s subshell, and electrons are being added to the 2 p subshell in the atoms from B to Ne. In the first period the distinguishing electrons for H and He are in the 1 s subshell. The first three horizontal rows or periods in the modern periodic table consist entirely of representative elements. Formulas for chlorides of the first dozen elements that show the periodic variation of valence Element This agrees with the valence rules derived from the periodic table, and results in formulas for chlorides of the first dozen elements that show the periodic variation of valence. For representative elements the number of valence electrons is the same as the periodic group number, and the number needed to match the next noble-gas configuration is 8 minus the group number. That is, the valences of the representative elements may be predicted on the basis of the number of valence electrons they have, or from the number of electrons that would have to be added in order to attain the same electron configuration as an atom of a noble gas. Many of the chemical properties of the representative elements can be explained on the basis of Lewis diagrams. Most of the elements whose chemistry and valence we have discussed so far fall into this category. The representative elements are those in which the distinguishing electron enter an s or p subshell. The type of subshell ( s, p, d, f)into which the distinguishing electron is placed is very closely related to the chemical behavior of an element and gives rise to the classification shown by the color-coding on the periodic table seen here. This last electron is called the distinguishing electron because it distinguishes an atom from the one immediately preceding it in the periodic table. Since it is the outermost (valence) electrons which are primarily involved in chemical interactions between atoms, the last electron added to an atom in the building-up process is of far more interest to a chemist than the first. The commonly used long form of the periodic table is designed to emphasize electron configurations.
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