8.1. Ions http://www.ck12.org
Cations and Anions
Metals will typically lose electrons to achieve stability, while non-metals typically gain electrons to achieve stability.
Two atoms or ions with the same number of electrons are referred to asisoelectronic.
FIGURE 8.2
Cations and AnionsCations
A positively charged ion is called acation. Main group metals will typically form ions by losing enough electrons
to become isoelectronic with the nearest noble gas. For example, lithium, whose configuration is [1s^2 2s^1 ], will
typically lose one electron to become isoelectronic with helium, which has a configuration of [1s^2 ] (seeFigure8.1).
Li
[He] 2 s^1
→Li+
[He]+e−Similarly, beryllium has 4 electrons (with the configuration [1s^2 2s^2 ]), so it prefers to lose two electrons, in order to
become isoelectronic with helium (again, [1s^2 ]).
Be
[He] 2 s^2
→Be^2 +
[He]+2e−Transition Metal Cations
As we saw in our chapter on the periodic table, the valence electrons for transition metals are variable, and electrons
in the highest occupied d orbitals (which are not part of the valence shell) may or may not be lost in the formation of a
transition metal cation. As a result, many transition metals commonly form more than one type of cation, depending
on how many d electrons are lost. Figure8.3 depicts some of the typical electron arrangements for the transition
elements.
Anions
A negatively charged ion is called ananion. Nonmetals will typically form ions by gaining enough electrons to
become isoelectronic with the nearest noble gas. For example, fluorine has 7 valence electrons and is one electron
away from being isoelectronic with neon, which has a stable noble gas electron configuration (seeFigure8.1).
F
[He] 2 s^22 p^5
+e−→ F−
[He] 2 s^22 p^6 or[Ne]Oxygen has 6 valence electrons in its ground state. Remember that ground state refers to the neutral atom in which
the electrons occupy the lowest possible energy positions. Oxygen is two electrons away from being isoelectronic