Each of the following compounds contains a metal that can exhibit more than one ionic charge. Name these compounds (a) \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{FeCl}_{2}\) (c) \(\mathrm{CrO}_{3}\) (d) \(\mathrm{Ti} \mathrm{Cl}_{4}\) (e) \(\mathrm{CoCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) (f) \(\mathrm{MoS}\) \(_{2}\)

Understanding the oxidation states of elements is crucial when naming chemical compounds. Oxidation states, often referred to as oxidation numbers, indicate the degree of oxidation or reduction of an atom in a chemical compound. Generally, it represents the number of electrons an atom has gained, lost, or shared when bonding.

For transition metals, which often have multiple possible oxidation states, determining the correct state is necessary for correct nomenclature. For instance, iron can exist in a +2 (ferrous) or +3 (ferric) oxidation state. Knowing the anion it's paired with helps determine the metal's oxidation state in a particular compound. If paired with oxygen, which typically has a -2 oxidation state, you could calculate the metal's state by balancing the total charge of the compound. Students can improve their grasp of this concept by practicing with elements across different groups of the periodic table and becoming familiar with common oxidation states.

The ionic charge of an element in a compound stems from its ability to lose or gain electrons to achieve a stable electronic configuration. Metals tend to lose electrons, forming positively charged ions (cations), while nonmetals tend to gain electrons, forming negatively charged ions (anions).

To name compounds, especially with metals showing more than one common ionic charge, it's essential to first determine the ionic charge of each atom. For example, FeCl₂ suggests that iron has a +2 ionic charge since two chlorine ions with a -1 charge each are required to balance the iron cation. Therefore, this compound is named iron(II) chloride. Practicing with the ionic charges of different elements helps students gain confidence in predicting and naming complex compounds.

Binary compounds consist of two different elements. Naming these compounds requires knowing the names of the elements involved and their respective oxidation states. The cation (metal) is named first, followed by the anion (nonmetal) with an 'ide' suffix. When the metal can have more than one oxidation state, Roman numerals are used to indicate the metal's charge, like in chromium(III) oxide (Cr₂O₃).

Students can improve their nomenclature skills by practicing with compounds of increasing complexity, starting with those that have fixed oxidation states, and then moving to those with variable charges. Remembering that the metal is named as per its elemental name while the nonmetal suffix changes to 'ide' can be a helpful mnemonic.

Hydrated compounds include water molecules within their crystalline structure. The naming of such compounds follows the naming of the anhydrous part of the compound followed by a prefix indicating the number of water molecules and the word 'hydrate'. The prefixes originate from Greek, where 'mono' indicates one, 'di' two, 'tri' three, and so on.

For instance, CoCl₂·6H₂O is called cobalt(II) chloride hexahydrate. To successfully name hydrated compounds, it's important to correctly determine the number of water molecules and use the fitting prefix before the term 'hydrate'. This concept can be better understood through hands-on practice with different hydrates and memorization of Greek numerical prefixes.