Question

why is fecl₃ called iron (iii) chloride? there is only one iron in the compound - why isnt it called iron (i) chloride? or why isnt it called iron chloride (iii)? to answer this question, its important to note that only the charge of the metal ion is specified in the name. this is because nonmetals usually do not form multiple ions. so we have to specify the charge on the metal ion if it forms more than one charge.
so, why isnt this compound called iron (i) oxide? thats because we have to name the charge of the iron cation, not the number of iron cations. how do we know the charge of the iron cation is +3? thats because we know from this chart that chlorine can only form a -1 ion. if there are three chlorine atoms, that means that, together, they form a -3 charge. the one iron cation must have a charge of +3 to create a neutral compound.
use the logic above to write out the chemical formula for chromium (iii) chloride. you may need to use this table.
make sure to answer the question on this screen before moving on.

Explanation:

Step1: Determine the charge of chromium ion

Chromium (III) has a charge of \(+3\).

Step2: Determine the charge of chloride ion

Chloride ion has a charge of \(-1\).

Step3: Use the criss - cross method

For a neutral compound, let the formula be \(Cr_xCl_y\). Using the charge balance \(+3x+(- 1)y = 0\). To get the smallest whole - number ratio, when \(x = 1\), \(y=3\).

Answer:

\(CrCl_3\)