![]() In contrast to the chemistry of the second-period elements, the chemistry of the third-period elements is more representative of the chemistry of the respective group.ĭue to their small radii, second-period elements have electron affinities that are less negative than would be predicted from general periodic trends. The anomalous chemistry of second-period elements results from three important characteristics: small radii, energetically unavailable d orbitals, and a tendency to form pi (π) bonds with other atoms. Consequently, the elements of the third period (n = 3: Na, Mg, Al, Si, P, S, and Cl) are generally more representative of the group to which they belong. The chemistry of the second-period element of each group (n = 2: Li, Be, B, C, N, O, and F) differs in many important respects from that of the heavier members, or congeners, of the group. Unique Chemistry of the Lightest Elements The semimetals lie along the diagonal line separating the metals from the nonmetals and exhibit intermediate properties. Consequently, the elements in the upper right of the periodic table are the smallest and most electronegative the elements in the bottom left are the largest and least electronegative. A high electronegativity value means an atom readily attracts electrons to form a chemical bond with another atom. It is a scalar quantity meaning that the applied electric field can only produce polarizability. The unit of polarizability is C·m 2 ·V -1. Mathematically, it can be determined from the following equation. Electronegativity is a measure of how easily an atom attracts a pair of electrons to form a chemical bond. In chemistry, periodicity refers to repeating trends in element properties on the periodic table. The polarizability () of a substance is the ratio of the induced dipole moment ( ind) to the applied electric field (E). 1 separates the metals (to the left of the line) from the nonmetals (to the right. In contrast, atomic size decreases from left to right and from bottom to top. Periodic table showing the trend from low to high of the element’s electronegativity. Recall that these trends are based on periodic variations in a single fundamental property, the effective nuclear charge ( Zeff Z e f f ), which increases from left to right and from top to bottom in the periodic table. Ionization energies, the magnitude of electron affinities, and electronegativities generally increase from left to right and from bottom to top. \): Summary of Periodic Trends in Atomic Properties.
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