Ionic compound

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Long before chemists knew the formulas for chemical compounds, they developed a system of writing binary formulas nacl that gave each compound a unique name. But we still need unique names that unambiguously identify each compound.

Some compounds have been known for so long that a systematic nomenclature cannot compete with well-established common names. The names of ionic compounds are written by listing the name of the positive ion followed by the name of the negative ion. We therefore need a series of rules that allow us to unambiguously name positive and negative ions before we can name the salts these ions form.

Some metals form positive ions in more than one oxidation state. One of the earliest methods of distinguishing between these ions used the suffixes -ous and -ic added to the Latin name of the element to represent the lower and higher oxidation states, respectively. Chemists now use a simpler method, in which the charge on the ion is indicated by a Roman numeral in parentheses immediately after the name of the element.

Negative ions that consist of a single atom are named by adding the suffix -ide to the stem of the name of the element. Predict the formula of the compound that forms when magnesium metal reacts with nitrogen to form magnesium nitride. Click here to check your answer to Practice Problem 4. At first glance, the nomenclature of the polyatomic negative ions in the table above seems hopeless.

There are several general rules, however, that can bring some order out of this apparent chaos. The name of the ion usually ends in either -ite or -ate. The -ite ending indicates a low oxidation state. Thus,the NO 2 - ion is the nitrite ion. The -ate ending indicates a high oxidation state. The NO 3 - ion, for example, is the nitrate ion. The prefix hypo - is used to indicate the very lowest oxidation state.

The ClO- ion, for example, is the hypochlorite ion. The prefix per - as in hyper- is used to indicate the very highest oxidation state.

The ClO 4 - ion is therefore the perchlorate ion. There are only a handful of exceptions to these generalizations. The names of the writing binary formulas nacl OH -cyanide CN -and peroxide O 2 2- writing binary formulas nacl, for example, have the -ide ending because they were once thought to be monatomic ions. The bone and tooth enamel in your body contain ionic compounds such as calcium phosphate and hydroxyapatite.

Click here to writing binary formulas nacl your answer to Practice Problem 5. Oxidation states also play an important role in naming simple covalent compounds. The name of the atom in the positive oxidation state is listed first. The suffix -ide is then added writing binary formulas nacl the stem of the name of the atom in the negative oxidation state.

As a rule, chemists write formulas in which the element in the positive oxidation state is written first, followed by the element s with negative oxidation numbers. The number of atoms of an element in simple covalent compounds is indicated by adding one of the following Greek prefixes to the name of the element. The prefix mono - writing binary formulas nacl seldom used because it is redundant.

The principal exception to this rule writing binary formulas nacl carbon monoxide CO. These solutions are named by adding the prefix hydro - to the name of the compound and then replacing the suffix -ide with -ic. For example, hydrogen chloride HCl dissolves in water to writing binary formulas nacl hydrochloric acid; hydrogen bromide HBr forms hydrobromic acid; and hydrogen cyanide HCN forms hydrocyanic acid.

Many of the oxygen-rich polyatomic negative ions in Table 2. Practice Problem 4 Predict the formula of the compound that forms when magnesium metal reacts with nitrogen to form magnesium nitride. Practice Problem 5 The bone and tooth enamel in your body contain ionic compounds such as calcium phosphate and hydroxyapatite. Acids containing ions ending with ide often become.

Acids containing ions ending with ate writing binary formulas nacl become. Acids containing ions ending with ite usually become.

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Binary compounds contain two and only two chemical elements. The name of a compound is derived from the names of its elements and some general agreements among chemists.

This gives us the following procedures: The name of an inorganic compound is made up of the names of the elements of which it is composed. The elements are always named in the order most metallic to least metallic. The name of the second element in a binary compound is modified to end in -ide. Naming compounds is fairly easy. Every elements symbol starts with a capital and sometimes has a second lower-case letter after it.

Look at the molecule and divide it up into the positive and negative elements. Name the positive element first, followed by the negative element. Na is sodium, Cl is chlorine but in a compound it is modified to chloride. So the name is Sodium chloride. The number of I is not important for naming purposes, at least not yet.

Sr is strontium and I is iodine which is modified to be iodide. So the name is strontium iodide. Stop here and do Nomenclature Exercise 1. Identify the elements with their symbols. Write the positive element first followed by the second element.

Look on the periodic table and find the valences of the elements and write them in above and to the right of the symbols as superscripts. Cross multiply the valences and place the numbers as subscripts below and to the right of the symbol. Stop and check that the total positive charges and total negative charges balance out to zero 0.

If the numbers generated are divisible by a common denominator then divide them to get the lowest possible numbers. Erase the superscripts and any ones 1 because a "1" is always assumed. What is the formula for calcium chloride? CaCl 2 The formula of calcium chloride is CaCl 2. What is the formula for Sodium nitride? Na 3 N The formula of sodium nitride is Na 3 N. Stop here and do Nomenclature Exercise 2. These ions are made up from 2 or more different types of atoms.

Quite often they have a non-metal atom which is capable of different valences. It is probably best at this time for you to commit these to memory and worry about how they are formed until later. The rules for putting these together remains the same. There is one additional rule. If you need more than 1 of a polyatomic ion, indicate this with brackets and a subscript.

The superscripts which indicated charges are gone. They have been replaced by subscripts that give the numbers of each kind of ion. The overall charge on the entire molecule is zero 0. The positive ion is written and named first. This is because it is the most electropositive. The negative ion is written and named second because it is not as electropostive.

As a matter of fact it is very electronegative. The above ions have a -3 charge. Treat them as if they were a single atom ion by placing brackets around them when necessary. If the rules for cross multiplying are followed you could end up with Sr 2 SO 4 2 as an answer.

This is a case where you have a common number between the two groups that can be easily divided. In this case by 2. No brackets are needed or should be included. Since ammonium is polyatomic we must put brackets around it indicating that we need two complete ammonium ions. Stop here and do Nomenclature Exercise 3. The same rules apply for making up formulas and names. Positive ions are written and named first followed by the negative ions. Stop here and do Nomenclature Exercise 4.

The nomenclature work that you have done so far is all that is needed if only one binary compound of the two elements exists. Many combinations of two elements, however, can result in more than one compound. For example, iron and chlorine react to produce both FeCl 2 and FeCl 3 , which have demonstrably different properties, and so the name iron chloride is ambiguous.

Whenever two or more compounds of the same two elements are possible, one of two approaches to modifying the name is used. Both approaches are valid, although one may be more appropriate with a particular compound than the other. Very few compounds are named using both approaches. The first of these approaches taken when two or more different compounds of the same elements exist is the oxidation state approach, also called the Stock system after the chemist A.

It can be rationalized in the following simple discussion, which is a brief summary of a more elaborate discussion we will take up later. The oxidation state of an element in a compound is denoted by placing a Roman numeral after the name of the element.

Oxidation states are given if and only if they are necessary to make the name unambiguous. In the case of iron chloride, oxidation states should be used. Calculation of the oxidation state of an element when it is combined in a compound or ion has many different approaches. It usually depends on who is teaching it and how they first learned it themselves from their teachers. It can be done by the application of one definition and a few general properties of some of the common elements.

The definition is as follows: The sum of the oxidation states of all the elements in a compound is zero ; the sum of the oxidation states in an ion positively or negatively-charged species is equal to the net charge on the ion. The properties of the elements used to determine oxidation state are, in order of precedence: There are virtually no exceptions. The only significant exceptions are the peroxides, such as H 2 O 2 and Na 2 O 2 , in which the oxygen is in the -1 oxidation state.

The only significant exceptions are the saline hydrides, such as LiH, in which hydrogen is in the -1 oxidation state. The only significant exceptions are those compounds of the halogens which also include oxygen, such as NaClO 4. Most of the transition metals have several different oxidation states.

Putting them in is not incorrect but it would be a chemical social faux paus. To name the compound NiO 2 , first name the elements: Second, change the ending: Third, calculate the oxidation state of nickel: This gives the name: The oxidation state of oxygen need not be specified. To name the compound V 2 O 5 , first name the elements: Third, calculate the oxidation state of vanadium: There is an older nomenclature for compounds with variable oxidation state traceable to Lavoisier, in which the higher oxidation state of an element is designated by an -ic ending on the element name and the lower by an -ous ending, as vanadous oxide VO and vanadic oxide V 2 O 3.

Since this system fails when more than two oxidation states are known for the same element, and the numeric oxidation state designated by -ic or -ous endings changes from element to element, it is obsolete. Modern chemists no longer use it for binary compounds, although traces of it still remain in the nomenclature of less simple compounds. Some commercial manufacturers, however, still label their products in the old way. The older method was made up based on the few metals that were known in the past.

The name also is derived from the old name of the elements. As you can see above these metals only had two possible valences. A system that distinguishes between only two is fine and that is what the "ous"-"ic" system did.

The lower valence metal had its named changed to end in "ous" while the higher valence metal had its names changed to end in "ic". In the James Bond movie Goldfinger who was the villian? What was the license plate number on Goldfinger's Rolls Royce? What was the name of Goldfinger's business establishment? This system work's quite well with elements possessing 2 possible valences.

The problem lies in the fact that a few elements have more than two valences. Using the "ous"-"ic" system we could only name the first two lowest valences. It is for this reason that the Stock system is in prominent use today. Stop here and do Nomenclature Exercise 5.