Summary
Highlights
Transition metals are elements in the central block of the periodic table, and their ionic compounds often include Roman numerals in their names. These Roman numerals indicate the charge of the transition metal ion. For those new to the topic, prior videos on 'Writing Ionic Formula Introduction' and 'Transition Metals in Ionic Compounds' are recommended.
To write the formula for chromium (II) iodide, first determine the charges of the ions. The Roman numeral 'II' in chromium (II) indicates a 2+ charge for chromium (Cr). Iodine (I), located in a specific column on the periodic table, always forms an ion with a 1- charge (iodide). To balance the charges, one Cr2+ ion requires two I- ions, resulting in the formula CrI2. A common misconception is to associate the Roman numeral with the number of atoms, rather than the ionic charge.
For manganese (III) oxide, manganese (Mn) is a transition metal that can form various ions. The Roman numeral 'III' specifies a 3+ charge for manganese in this compound. Oxygen (O) in an ionic compound always has a 2- charge (oxide). To balance a 3+ charge with a 2- charge, the least common multiple is 6. Therefore, two Mn3+ ions (total 6+) are balanced by three O2- ions (total 6-), yielding the formula Mn2O3. Again, the Roman numeral indicates charge, not the number of atoms.
Lead (Pb), although not strictly a transition metal, uses Roman numerals due to its ability to form multiple ions with differing charges. Lead (IV) denotes a 4+ charge for lead. Nitrate is a polyatomic ion (NO3-) with a 1- charge. To balance a 4+ charge from lead, four nitrate ions are needed. Since nitrate is a polyatomic ion, parentheses are used to indicate that there are four entire nitrate groups, resulting in the formula Pb(NO3)4. It is important to know common Roman numerals and polyatomic ions for these types of formulas.
This video demonstrated how to write ionic formulas when given the name of a compound containing a transition metal. The next video will cover the reverse process: starting with an ionic formula containing a transition metal and determining its name, which involves calculating the charge of the transition metal ion.