In health science, we distinguish between ionic compounds (electrolytes) and molecular compounds (like sugars and gases) because they behave differently in the human body.
An ionic compound has one or more ionic bonds. An ionic bond is a strong electrostatic attraction between a cation and an anion.
For an ion to be created, one or more electrons must leave or enter an atom.
When electrons leave an atom, a (+) cation is created; when electrons enter an atom, a (-) anion is created.
Sodium (Na) has 11 electrons and proton. One of them is able to leave the atom to create a sodium cation (Na+ with only 10 electrons and still has 11 protons and hence the + charge)
Metals form cations; nonmetals form anions.
NaCl is an ionic compound between Na+ and Cl- (1:1 ratio)
CaCl2 is an ionic compound between Ca2+ and 2 Cl- (1:2 ratio)
Al2O3 is an ionic compound between 2 Al3+ and 3 O2- (2:3 ratio)
Both cations and anions are written by their atomic symbol, followed by their positive or negative charge as a superscript.
Metals cations keep the same name:
Ca -> Ca2+ calcium ion
Fe -> Fe2+ or Fe3+ iron ion (though we may say iron (ii) or iron (iii) cation.
Nonmetals change their name by adding a suffix of ‘-ide’
Cl -> Cl- chlorine becomes a chloride ion
O -> O2- oxygen becomes an oxide ion
When a single atom (metal or nonmetal) forms an ion, these are called monoatomic ions.
However, there also exist several types of polyatomic ions, which contain two or more elements that are molecules with an overall positive or negative charge.
Ionic compounds can also have polyatomic ions present.
Calcium carbonate is an ionic compound formed with Ca2+ and the polyatomic carbonate ion (CO32-) to form CaCO3.
Magnesium hydroxide is formed by Mg2+ and 2 hydroxide ions (OH-) as Mg(OH)2 … note here that because the hydroxide is a ‘unit’ and there needs to be two of them to counteract the 2+ on Mg2+, the hydroxide must be placed in parentheses before the subscript.
MgOH2 is incorrect!
Some ions consist of multiple atoms acting as a single charged unit. These are vital for maintaining blood pH and cellular energy.
| Name | Formula |
|---|---|
| Ammonium | NH4+ |
| Hydronium | H3O+ |
| Hydroxide | OH- |
| Cyanide | CN- |
| carbonate | CO32- |
| bicarbonate | HCO3- |
| nitrate | NO3- |
| nitrite | NO2- |
| sulfate | SO42- |
| phosphate | PO43- |
NH3 is the molecule ammonia … adding another hydrogen creates the ammonium cation, NH4+
Water (H2O) can create a cation by adding a hydrogen called the hydronium ion (H3O+) or an anion by losing a hydrogen, called the hydroxide ion (OH-)
| Ions | Compound Formula | Name |
|---|---|---|
| Na+ + OH- | NaOH | Sodium hydroxide |
| Mg2+ + 2OH- | Mg(OH)2 | Magnesium hydroxide |
| Al3+ + 3OH- | Al(OH)3 | Aluminum hydroxide |
| K+ + CO32- | K2CO3 | Potassium carbonate |
C6H12O6 (Glucose) is molecular. Na2CO3 and KCN contain metal cations (Sodium and Potassium) paired with polyatomic anions, making them ionic.
Let’s practice a few … write out the formulas for the following ionic compounds:
answers
Ionic bonds, again, are strong electrostatic attractions between cations and anions. When cations and anions come together, they do so in a fixed ratio that ensures a neutral compound.
Compounds are held together by bonds. Recognizing the difference between ionic and molecular compounds helps predict how a substance will dissolve or react in the bloodstream.
Formed by the transfer of electrons, creating an attraction between oppositely charged ions. Normally ionic compounds are formed from when an alkali/alkaline metal that loses an electron bonds with an atom from the right side of the periodic table that gained an electron.