Binary compound is a compound composed of only two elements non metals or metalloids .
Binay compound are usually molecular and are named using a prefix system.
Order of elements in the formula : The order of elements in the formula of a binary molecular compound is established by convention.By this convention, the nonmetal or metalloid occuring first in the following sequence is written first in the formula of the compound.
element B} IIIA gp element Si , C } IV A group , element Sb,As,P,N,}VA group , H , Te, Se,S,}VIA , I,Br,Cl} VIIA , O , F
You can reproduce this order easily if you have a periodic table available.You arrange the non metals and metalloids in the order of the groups of the periodic table, listing the elements from the bottom of the group upward.Then you place hydrogen between group VA and VIA and move O so that it is just before F.
Note : This order places the nonmetals and metalloids in the order of increasing non metallic character. Thus, in the formula , the first element is the more metallic and second element is the more nonmetallic . For example : the compound whose molecule contains three fluorine atoms and one nitrogen atom is written NF3 and F3N.
Rules for naming binay molecular compounds:
1. The name of the compound has the elements in the order given in the formula.
2. You name the first element using exact elements name.
3.You name the second element by writing the stem name of the elements with the suffix -ide .
4. You add a prefix derived from the Greek, to each element name to denote the subscript of the element in the formula.Generally the prefix mono is not used, unless it is needed to distiguish two compounds of the same two elements.
For example: consider N2O3
This is a binary molecular compound, as you would predict because N and O are nonmetals.According to Rule 1 you name it after the elements,N before O , following the order of elements in the formula.By rule 2 , the N is named exactly as the element (nitrogen) , and by Rule 3 , the O is named as the anion (oxide) .The compound is a nitrogen oxide.Finally ,you shows the prefix for two is di , and prefix for three is tri- . The name of the compoound is dinitrogen trioxide.
Here are some example to illustrate how the prefix mono is used
in HCL there is only one hydrogen and one chlorine HCl .It is called hydrogen chloride and not monohydrogen monochloride.
There are two compounds of carbon and oxygen :CO & CO2 .They are both carbon oxides.To distinguish one from other, we name them carbon monoxide respectively.
Few more examples:
SF4 - sulfur tetrafluoride , ClO2 - chlorine dioxide , Cl2O7 - dichlorine heptaoxide.
prefixes for naming compounds
1 - mono
9 - nona
10 - deca