Periodic Properties of Atoms
The Periodic Properties of Atoms
The Periodic Table: In the 1870's, the Russian chemist Mendeleev developed the periodic table, based upon the relationship between the atomic weights of the elements and their chemical properties. As one ascends from lightest to heaviest elements, there is a periodic recurrence of chemical properties. For example, the elements with atomic numbers 2, 10, 18, 36, 54, and 86 all are chemically inert (the noble gases), while those with atomic numbers one greater 3, 11, 19, 37, 55, and 87 are all extremely reactive metals (the alkali metals).
The rows or periods of the periodic table contain the elements with the same principle quantum number (n) for their outermost electrons. That is, until the fourth period, which contains the first row of transition metals, where the electrons of highest energy exist in d orbitals, which follow in the building-up order s orbitals of a higher shell, being grouped in the same period with elements of higher principle quantum number (n). The columns or groups in the periodic table contain elements with the same electron configuration in the outermost shell. For example, the outermost shell of a noble gas is completely filled, while the outermost shell of an alkali metal contains only one electron. Examine the periodic table at right showing which subshell contains the highest energy electrons in the ground state of each element. Compare to the table above to understand how the periodic nature of chemical properties corresponds to the configuration of outer-shell electrons. Notice that the blocks into which the table above is subdivided correspond to the type of subshell, s, p, d, or f and therefore to the momentum quantum number (l).
© J.S. Wetzel, 1993
Periodic Properties As one reads across the periodic table from left to right in a given period, the pull exerted upon the outer-shell electrons by the positively charged nucleus increases with atomic number. There are more protons in the
The Periodic Table: In the 1870's, the Russian chemist Mendeleev developed the periodic table, based upon the relationship between the atomic weights of the elements and their chemical properties. As one ascends from lightest to heaviest elements, there is a periodic recurrence of chemical properties. For example, the elements with atomic numbers 2, 10, 18, 36, 54, and 86 all are chemically inert (the noble gases), while those with atomic numbers one greater 3, 11, 19, 37, 55, and 87 are all extremely reactive metals (the alkali metals).
The rows or periods of the periodic table contain the elements with the same principle quantum number (n) for their outermost electrons. That is, until the fourth period, which contains the first row of transition metals, where the electrons of highest energy exist in d orbitals, which follow in the building-up order s orbitals of a higher shell, being grouped in the same period with elements of higher principle quantum number (n). The columns or groups in the periodic table contain elements with the same electron configuration in the outermost shell. For example, the outermost shell of a noble gas is completely filled, while the outermost shell of an alkali metal contains only one electron. Examine the periodic table at right showing which subshell contains the highest energy electrons in the ground state of each element. Compare to the table above to understand how the periodic nature of chemical properties corresponds to the configuration of outer-shell electrons. Notice that the blocks into which the table above is subdivided correspond to the type of subshell, s, p, d, or f and therefore to the momentum quantum number (l).
© J.S. Wetzel, 1993
Periodic Properties As one reads across the periodic table from left to right in a given period, the pull exerted upon the outer-shell electrons by the positively charged nucleus increases with atomic number. There are more protons in the