Nomenclature of Ionic Compounds
Ionic compounds consist of cations (positive ions) and anions (negative ions).
A. Simple binary compounds
- compounds that contain two elements
Steps to follow to obtain the chemical formula:
1) Know the charges of the ions involved
-ionic compounds are combinations of positive and negative ions, generally formed when nonmetals and metals bond
2) make a neutral molecule: the positive charge of the cation (positively-charged ion) must equal the negative charge of the anion (negatively-charged ion)
-to create a neutral charged molecule, you must combine the atoms in certain proportions
3) Write the compound with the more positively charged element being first.
ex. magnesium nitride
when combining magnesium and nitrogen we know that the magnesium ion has a "+2" charge and the nitrogen ion has a "-3" charge. To cancel these charges, we must have three magnesium atoms for every two nitrogen atoms:
Mg2+ + N3- --> Mg3N2
Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.
Steps to follow to obtain the name from a formula:
- the name is made of two parts
name of first element root of name of second element + “ide”
ex. NaCl
sodium chlorIDE
2. Ions with multiple charges
-Some atoms can commonly form 2 or 3 different charges, typically transition elements. (look on periodic table), ex. Copper, for example, usually forms +1 or +2 charged ions.
-This can cause problems if a compound is named Copper Oxide. This could have the formula CuO or Cu2O depending on the charge of the copper atom.
-To clear up this ambiguity we can name the ions by specifically adding on a number to their name. Cu+1 is Copper(I) and Cu+2 is Copper(II). So the names of the copper compounds listed above are Copper(II)Oxide for CuO and Copper(I)Oxide for Cu2O.
-A Roman numeral in parentheses, followed by the name of the element, is used for elements that can form more than one positive ion.
Fe2+ Iron (II), Fe3+ Iron (III), Cu+ Copper (I), Cu2+ Copper (II)
Try some examples below:
Iron(II)Oxide = CuSO4
Iron(III)Oxide = Cr(NO3)3