While studying about ions in your chemistry textbook, you’ll come across two kinds of ions – anions and cations. In any case, either an atom can have a balanced number of electrons and protons, or they can be unbalanced. In the latter case, an atom has a charge on it, and these charged species are ions. In this guide, you’ll learn some of the main differences between anions and cations. First, let’s learn the basics of an ion.
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What is an Ion?
Ions are atoms or groups of atoms that bear one or more positive or negative electrical charge. Among the two charges of an ion, the positive one is known as a cation, while the negative one is known as an anion. The formation of an ion takes place either by the addition of electrons or by removal of electrons, neutral atoms or molecules or other ions. In the process, a covalent bond between the two atoms ruptures in a way that both the participating electrons are left behind with one of the formerly bonded atoms.
Types of Ions
Now that you know how the formation of ions takes place, you must also know the major differences between the two types.
Anions
- An anion is an atom or a group of atoms bearing one or more negative electric charges.
- Organic anions are termed carbanions.
- Anions are formed from nonmetal atoms.
- Anions are attracted towards the positive terminal (cathode) of an electric field.
- Some examples of anions are SO4—, Cl–, F–, PO4—and I–.
Cations
- A cation is an atom or a group of atoms bearing one or more positive electric charges.
- Organic cations are termed carbocations.
- Cations carry one or more positive charges.
- Cations are formed from metal atoms.
- Cations are attracted towards the negative terminal (anode) of an electric field.
- Some examples of cations are Na+, K+, NH4+, Ca2+, and Al3+.
How to Determine the Ion Type Using Periodic Table?
Did you know, it is easy to determine the type of an atom between positive or negative using a periodic table? Halogens always form anions, whereas alkali metals and alkaline earth metals always form cations. In short, most metals in the table form cations while most nonmetals typically form anions under the right conditions. In contrast, the elements in group 18 of the periodic table are called noble gases, which tend not to form ions due to its electron arrangement and are unreactive.
The Rule of Writing Chemical Formulas
While writing the chemical formula of a compound, the cation is always listed before the anions.
For example:-
In NaCl, the sodium atom acts as the cation, while the chlorine atom acts as the anion.
And while writing cation or anion symbols, the element symbols’ listing takes place first. In this case, the charge is written as a superscript following the chemical formula.
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