For main group elements, the last orbital gains or loses the electron. Remember electrons are negatively charged, so ions with a positive charge have lost an electron. Next, determine whether an electron is gained or lost. We have chosen to show the full, unabbreviated configurations to provide more practice for students who want it, but listing the core-abbreviated electron configurations is also acceptable. Predicting Electron Configurations of Ionsįirst, write out the electron configuration for each parent atom. The two additional electrons required to fill the valence orbitals give the oxide ion the charge of 2– (O 2–). Oxygen, for example, has the electron configuration 1 s 22 s 22 p 4, whereas the oxygen anion has the electron configuration of the noble gas neon (Ne), 1 s 22 s 22 p 6. Thus, it is simple to determine the charge on such a negative ion: The charge is equal to the number of electrons that must be gained to fill the s and p orbitals of the parent atom. Most monatomic anions form when a neutral nonmetal atom gains enough electrons to completely fill its outer s and p orbitals, thereby reaching the electron configuration of the next noble gas. Electronic Structures of AnionsĪn anion (negatively charged ion) forms when one or more electrons are added to a parent atom. When the inner transition metals form ions, they usually have a 3+ charge, resulting from the loss of their outermost s electrons and a d or f electron. Although the d orbitals of the transition elements are-according to the Aufbau principle-the last to fill when building up electron configurations, the outermost s electrons are the first to be lost when these atoms ionize. Click here for an exampleįor example, iron (1s 22s 22p 63s 23p 63d 64s 2) forms the ion Fe2+ (1s 22s 22p 63s 23p 63d 6) by the loss of the 4s electron and the ion Fe3+ (1s 22s 22p 63s 23p 63d 5) by the loss of the 4s electron and one of the 3d electrons. Most transition metal cations have 2+ or 3+ charges that result from the loss of their outermost s electron(s) first, sometimes followed by the loss of one or two d electrons from the next-to-outermost shell. Transition and inner transition metal elements behave differently than main group elements. Mercury (group 12) also exhibits an unexpected behavior: it forms a diatomic ion, Hg 2 2+ (an ion formed from two mercury atoms, with an Hg-Hg bond), in addition to the expected monatomic ion Hg 2+ (formed from only one mercury atom). The formation of these 1+, 2+, and 3+ cations is ascribed to the inert pair effect, which reflects the relatively low energy of the valence s-electron pair for atoms of the heavy elements of groups 13, 14, and 15. In addition to the expected ions Tl 3+, Sn 4+, Pb 4+, and Bi 5+, a partial loss of these atoms’ valence shell electrons can also lead to the formation of Tl +, Sn 2+, Pb 2+, and Bi 3+ ions. Click here to learn more!Įxceptions to the expected behavior involve elements toward the bottom of the groups. For example, aluminum (in group 13) forms 3+ ions (Al 3+).Īs always, there are exceptions. Thus, the charge of a cation formed by the loss of all valence electrons is equal to the group number minus 10. The Ca 2+ ion is therefore isoelectronic with the noble gas Ar.įor groups 13–17, the group numbers exceed the number of valence electrons by 10 (accounting for the possibility of full d subshells in atoms of elements in the fourth and greater periods). When a Ca atom loses both of its valence electrons, the result is a cation with 18 electrons, a 2+ charge, and an electron configuration of 1 s 22 s 22 p 63 s 23 p 6. For example, calcium is a group 2 element whose neutral atoms have 20 electrons and a ground-state electron configuration of 1 s 22 s 22 p 63 s 23 p 64 s 2. For groups 1 (the alkali metals) and 2 (the alkaline earth metals), the group numbers are equal to the numbers of valence shell electrons and, consequently, to the charges of the cations formed from atoms of these elements when all valence shell electrons are removed. When forming a cation, an atom of a main group element tends to lose all of its valence electrons, thus becoming isoelectronic with the previous noble gas in the periodic table. Electronic structures of CationsĪ cation (positively charged ion) forms when one or more electrons are removed from a parent atom. Solid nonmetals are also very brittle.Ions are formed when atoms gain or lose electrons. A nonmetal is typically dull and a poor conductor of electricity and heat. Metals are also malleable (they can be beaten into thin sheets) and ductile (they can be drawn into thin wires). A metal is a substance that is shiny, typically (but not always) silvery in color, and an excellent conductor of electricity and heat.
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