Positive and Negative Ions: Cations and Anions
Cations (positively-charged ions) and anions (negatively-charged ions) are formed when a metal loses electrons, and a nonmetal gains those electrons. The electrostatic attraction between the positives and negatives brings the particles together and creates an ionic compound, such as sodium chloride.
A metal reacts with a nonmetal to form an ionic bond. You can often determine the charge an ion normally has by the element’s position on the periodic table:
The alkali metals (the IA elements) lose a single electron to form a cation with a 1+ charge.
The alkaline earth metals (IIA elements) lose two electrons to form a 2+ cation.
Aluminum, a member of the IIIA family, loses three electrons to form a 3+ cation.
The halogens (VIIA elements) all have seven valence electrons. All the halogens gain a single electron to fill their valence energy level. And all of them form an anion with a single negative charge.
The VIA elements gain two electrons to form anions with a 2- charge.
The VA elements gain three electrons to form anions with a 3- charge.
The first table hows the family, element, and ion name for some common monoatomic (one atom) cations. The second table gives the same information for some common monoatomic anions.
It’s more difficult to determine the number of electrons that members of the transition metals (the B families) lose. In fact, many of these elements lose a varying number of electrons so that they form two or more cations with different charges.
The electrical charge that an atom achieves is sometimes called its oxidation state. Many of the transition metal ions have varying oxidation states. The next table shows some common transition metals that have more than one oxidation state.
|VIB||Chromium||Chromium(II) or chromous|
|Chromium(III) or chromic|
|VIIB||Manganese||Manganese(II) or manganous|
|Manganese(III) or manganic|
|VIIIB||Iron||Iron(II) or ferrous|
|Iron(III) or ferric|
|Cobalt||Cobalt(II) or cobaltous|
|Cobalt(III) or cobaltic|
|IB||Copper||Copper(I) or cuprous|
|Copper(II) or cupric|
|IIB||Mercury||Mercury(I) or mercurous|
|Mercury(II) or mercuric|
|IVA||Tin||Tin(II) or stannous|
|Tin(IV) or stannic|
|Lead||Lead(II) or plumbous|
|Lead(IV) or plumbic|
Notice that these cations can have more than one name. The current way of naming ions is to use the metal name, such as Chromium, followed in parentheses by the ionic charge written as a Roman numeral, such as (II).