A. When an ionic compound is bonded, the charges on the two ions must be balance

Question

A.

When an ionic compound is bonded, the charges on the two ions must be balanced. If the positive ion has a charge of +2 and the negative ion is -2 then the charges are equal and we need one of each to balance the charges

X+21Y-21, the "1" is the subscript indicating the number of each ion needed and is generally not written

if X has a charge of positive 2 and Y has a charge of negative 1 then we will need two of the Y atoms to balance one of the X atoms.

X+21Y-12 which usually written XY2

The subscript times the charge on the positively charged ion must be equal to opposite of the subscript times the charge on the negative ion. 1 times +2 = - (1 times -2). We can simplify this by saying the charge on the negative ion become the subscript of the positive ion and the charge on the postive ion becomes the subscript on the negative ion. Be careful of the crossing rule, because if the numbers are not the simplest or smallest values, the answer is incorrect. For example Pb+4 with S2- is PbS2 not Pb2S4.

X and Y can be either a single atom or a polyatomic ion, the balancing of charge remains the same. If Y is AO32- and X is BH41+ then we would write

X2Y1 or (BH4)2AO3, notice when we need more than one polyatomic ion to balance the charge, the polyatomic ion is placed in ( ) with the subscript on the outside of the ( ).

The most common charges are +1, +2, and +3 for the cations and -1, -2 and -3 for the anions; therefore, there are limited combinations that can occur, XY, XY2, XY3, X2Y, X3Y. Occasionally you might have a +4 or +5 charge which would add to the possibilities.

Given the following constituent ions, what are the subscipts in the chemical formula of the ternary compound?

iron (III) hydrogen carbonate, Fe3+ and HCO31-

The compound is written Fex(HCO3)y

B.

Given the following constituent ions, what are the subscipts in the chemical formula of the ternary compound?

mercury (II) cyanide, Hg2+ and  CN1-

The compound is written HgBlank 1(CN)Blank 2  

-A.B.C.D.E.F. Fex x = ? Read Answer Items for Question 12 -A.B.C.D.E.F. (HCO3)y y = ? Read Answer Items for Question 12 Answer A. 1 B. 2 C. 3 D. 4 E. 5 F. 6

Explanation / Answer

a) x=1

y=3

b)hg=1

cn=2

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