When naming binary ionic compounds, name the cation first (specifying the charge, if necessary), then the nonmetal anion (element stem + -ide). These examples should help.24 What prefix should I use? Do you use prefixes for ionic compounds? If the ion ends in - ite then the acid will end in - ous. If it contains a polyatomic ion, then it is named ic acid if the ion ends in - ate. If an acid is a binary compound, it is named as hydroic acid. Knowing that oxygen's charge is always -2, we could determine that there were five oxygens and two vanadiums, if we were given the name without the formula. In the case of V 2O 5, it could also be called vanadium( V) oxide. The stock system is used when there is a metallic element in the compound. In the stock system, only the cation's number is written, and in Roman numerals. The less electronegative part is assigned a positive number. The most electronegative component of the molecule has a negative oxidation number that depends on the number of pairs of electrons it shares. This is essentially the roman numeral system that has already been explained, but it applies to non-ionic compounds as well. The second system, the stock system, uses oxidation numbers to represent how the electrons are distributed through the compound. A molecule containing three iodine atoms would be named triiodide. This does not, however, happen with di- and tri. Similar dropping occurs with mono- and elements beginning with o, as in the case of monoxide. That makes V 2O 5 divanadium pentoxide (instead of pentaoxide). If the last letter of the prefix is an a and the first letter of the element is a vowel, the a is dropped. The prefix system is used when both elements are non-metallic. A prefix is not necessary for the first element if there is only one, so SF 6 is 'sulfur hexafluoride'. If the substance is binary (containing only two elements), the suffix - ide is added to the second element. The first uses prefixes to indicate the number of atoms of an element that are in the compound. There are two systems of naming molecular compounds. Mercury (I) (Note: Mercury (I) is a polyatomic ion) Keep in mind that the roman numerals refer to the charge of the cation, not how many anions are attached.Ĭommon metal ions are listed below and should be learned: To be correct, you must write "copper( II) chloride" if you want CuCl 2 and "copper ( I) chloride" if you want CuCl. The charge must be balanced, so there would be one or two chloride ions to accept the electrons. If you wrote "copper chloride", it could be CuCl or CuCl 2 because copper can lose one or two electrons when it forms an ion. The name of an ionic compound must make it very clear what the exact chemical formula is. Many atoms (especially the transition metals) are capable of ionizing in more than one way. We now use the Stock system instead.įurther explanation of the roman numerals is in order. These Latin-based names are outdated, so it's not important to learn them. Common ions with this naming system include "plumbous/plumbic" for lead(II)/lead(IV) and "ferrous/ferric" for iron(II)/iron(III). In older texts, ions were assigned names based on their Latin root and a suffix. All other metals (except the Group 1 and 2 elements) must have roman numerals to show their charge.Ĭommon polyatomic ions that you should know are listed in the following table Aluminum will always have a charge of +3. Zinc always has a charge of 2+, so you don't have to name its charge either. Silver always has a charge of 1+, so it isn't necessary (but not wrong) to name its charge. The charge on the ion must be known, so it is written out for ions that have more than one common charge. In the last example, copper had a roman numeral 2 after its name because most of the transition metals can have more than one charge. K(HCO 3) - Potassium hydrogen carbonate.There is also a per- prefix, meaning one more oxygen atom than an - ate molecule has. Sometimes there can be a hypo- prefix, meaning one oxygen atom fewer than for - ite. The - ite suffix is used on the oxyanion with one oxygen atom fewer (like sulfite SO 3 2- or nitrite NO 2 -). The - ate suffix is used on the most common oxyanion (like sulfate SO 4 2- or nitrate NO 3 -). The chlorine family of ions is an excellent example. When different oxyanions are made of the same element, but have a different number of oxygen atoms, then prefixes and suffixes are used to tell them apart. Many of them contain oxygen and are called oxyanions. Wikipedia has related information at Polyatomic ion Between the periodic table and our knowledge of ionic bonding, we can determine the number of ions, based on which elements are used. Notice that there is no need to write how many ions there are.
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