MCAT Content / Ions In Solutions / Anion Cation Common Names Formulas And Charges For Familiar Ions

Anion, Cation: Common Names, Formulas and Charges for Familiar Ions

Topic: Ions In Solutions

Ionic compounds are named after their cation and anion.

Any atom or molecule with a net charge, either positive or negative, is known as an ion. Ions are formed when the number of protons in an atom does not equal the number of electrons. If more protons are present, the ion is positive and is known as a cation; if more electrons are present, the ion is negative and referred to as an anion. An ion consisting of a single atom is a monatomic ion; an ion consisting of two or more atoms is referred to as a polyatomic ion.

The table below shows the names and formulas of some common cations and anions.

An electrolyte is any salt or ionizable molecule that, when dissolved in solution, will give that solution the ability to conduct electricity. This is because when a salt dissolves, its dissociated ions can move freely in solution and allows a charge to flow. Electrolyte solutions are normally formed when an ionic salt is placed into a solvent such as water, the ionic solid dissociates into its respective cations and anions. For example, when table salt, NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction NaCl -> Na+ + Cl.

A strong electrolyte will completely dissociate into its component ions in solution; a weak electrolyte, on the other hand, will remain mostly undissociated in solution. An example of a weak electrolyte is acetic acid, which is also a weak acid.


Key Points

• Ions are formed when the number of protons in an atom does not equal the number of electrons. If more protons are present, the ion is positive and is known as a cation; if more electrons are present, the ion is negative and referred to as an anion.

• When ionic solids are dissolved in water or a solvent they form a solution of free cations and anions that can conduct electricity, this is known as an electrolyte.


Key Terms

Cation: A positively charged ion.

Anion: A negatively charged ion.

Electron: the subatomic particle that has a negative charge and orbits the nucleus; the flow of electrons in a conductor constitutes electricity.

Solution: A homogeneous mixture, which may be a liquid, gas, or solid, formed by dissolving one or more substances.

Solute: Any substance that is dissolved in a liquid solvent to create a solution.

Electrolyte: A substance that dissociates into ions when in solution.

Strong electrolyte: A solution/solute that completely, or almost completely, ionizes or dissociates in a solution.

Weak electrolyte: An electrolyte that does not completely dissociate in aqueous solution.

Salt: An ionic compound composed of cations and anions that are held together by electrostatic attraction.

Monatomic ion: An ion consisting of a single atom.

Polyatomic ion: An ion consisting of two or more atoms.



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