Positive and Negative Ions: Cations and Anions

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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 shows 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.

Some Common Monoatomic Cations
Family	Element	Ion Name
IA	Lithium	Lithium cation
	Sodium	Sodium cation
	Potassium	Potassium cation
IIA	Beryllium	Beryllium cation
	Magnesium	Magnesium cation
	Calcium	Calcium cation
	Strontium	Strontium cation
	Barium	Barium cation
IB	Silver	Silver cation
IIB	Zinc	Zinc cation
IIIA	Aluminum	Aluminum cation

Some Common Monoatomic Anions
Family	Element	Ion Name
VA	Nitrogen	Nitride anion
	Phosphorus	Phosphide anion
VIA	Oxygen	Oxide anion
	Sulfur	Sulfide anion
VIIA	Fluorine	Fluoride anion
	Chlorine	Chloride anion
	Bromine	Bromide anion
	Iodine	Iodide anion

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.

Some Common Metals with More than One Oxidation State
Family	Element	Ion Name
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).