Anions are atoms, or groups of atoms, which have more electrons than came with its atoms and thus have an overall negative charge. Cations are atoms, or groups of atoms, which have fewer electrons than came with its atoms and have the corresponding positive charge.
Additionally, both types of ions come in both monatomic single-atomed and polyatomic many atomed varieties. The charge on an ion is determined by the number of electrons the species has gained or lost.
Note that the zero charge shown in the example above is generally not shown and the absence of an indicated charge means the species is neutral. Monoatomic cations fall into two groups; those which always occur with a specific charge and those which can possess more than one charge. The first type is named simply by using the element name followed by the separate word ion.
Other monatomic cations can have more than one possible charge and the charge must be designated by a Roman Numeral in parentheses suffixed to the name of the element. These are nonmetal elements which have accepted extra electrons. These ions are relatively few in number and are listed below. Monatomic anions are named by taking the root of the element name and applying an -ide ending. Monatomic anions do not occur with multiple charges, thus each nonmetal can form only one monatomic anion, unlike some of the metals which can have multiple monatomic cations.
NOTE: the -ide ending for an anion name is reserved for monatomic anions with a few extremely important exceptions. Though, this is the last major group of ions we will consider, it is also the least easily mastered.
Anions in this group containing oxygen are referred to as oxyanions and are all named with an -ate or -ite ending. The most common oxyanion of an element is giving the -ate ending. NO 3 - nitr ate SO 4 2- sulf ate. CO 3 2- carbon ate PO 4 3- phosph ate.
ClO 3 - chlor ate BrO 3 - brom ate. An element may have two or more naturally occurring oxyanions and a system of prefixes and suffixes are used to indicate the number of oxygens contained in the oxyanion relative to the reference -ate oxyanion of the element. Ionic compounds consist of cations and anions which are attracted to one another forming a compound by association which has a neutral charge overall.
However, if they are not balanced, they will be charged. These charged species are called ions. A cation has more protons than electrons, consequently giving it a net positive charge. For a cation to form, one or more electrons must be lost, typically pulled away by atoms with a stronger affinity for them. The number of electrons lost, and so the charge of the ion, is indicated after the chemical symbol, e. An anion has more electrons than protons, consequently giving it a net negative charge.
For an anion to form, one or more electrons must be gained, typically pulled away from other atoms with a weaker affinity for them. The number of electrons gained, and so the charge of the ion, is indicated after the chemical symbol, e.
The main differences between cations and anions are summarized in the table below. It can be possible to predict whether an atom will form a cation or an anion based on its position on the periodic table.
Halogens always form anions, alkali metals and alkaline earth metals always form cations. The following elements have only one possible charge, so it would be incorrect to put a Roman numeral after their name. We will assume that all of the metallic elements other than those mentioned above can have more than one charge, so their cation names will include a Roman numeral. We know to put the Roman numeral in the name because manganese is not on our list of metals with only one charge.
There is only one common polyatomic ion. Cation Names and Formulas Help. Predicting Monatomic Cation Charges The atoms of the noble gases found in nature are uncombined with other atoms. Monatomic Cation Names The names of monatomic cations always start with the name of the metal, sometimes followed by a Roman numeral to indicate the charge of the ion. Polyatomic Cation Names There is only one common polyatomic ion.
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