What are Anions and Cations?

Anions and Cations

Cations (positively charged ions) and anions (negatively charged ions) are formed when a metal loses electrons, and non-metals gain those electrons. The electrostatic attraction between positives and negatives attracts particles to each other and creates an ionic compound, for example sodium chloride.

A metal reacts with a non-metal to form an ionic bond. Often the charge by an ion that it has normally had can be determined by the position of the element in the periodic table:

• Alkaline metals (the elements IA) lose an electron to form a cation with a 1+ charge.
• Alkaline metals on earth (the 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.
• Halogens (elements VIIA) have seven valence electrons. All halogens gain one electron to fill their valence energy level. And they all form an anion with a single negative charge.
• VIA elements gain two electrons to form anions with a 2- charge.
• VA elements gain three electrons to form anions with a 3- charge.

The first table shows the family, element, and ion names for some of the more common mono-atomic cations (one atom). The second table shows the same information for some of the more common mono-atomic anions.

It is more difficult to determine the number of electrons than the members of the transition metals (B families). In fact, many of these elements lose a variable number of electrons so that they form two or more cations with different charges.

The electrical charge that an atom reaches is sometimes called its oxidation state. Many of the transition metal ions have different oxidation states. The following table shows some common transition metals that have more than one oxidation state.

Note that these cations can have more than one name. The current way of naming ions is to use the name of the metal, such as chromium, followed in parentheses by the ionic charge written as a Roman numeral, such as (II).