create the exactly formula because that an ionic compound. Identify polyatomic ion in tennis2007.orgical formulas.

You are watching: Write the symbol for the cation in each of the following ionic compounds

Ionic compounds perform not exist as molecules. In the solid state, ionic compounds room in crystal lattice containing countless ions each of the cation and also anion. An ionic formula, prefer (ceNaCl), is an empirical formula. This formula merely suggests that salt chloride is make of an equal variety of sodium and also chloride ions. Sodium sulfide, another ionic compound, has the formula (ceNa_2S). This formula suggests that this compound is made up of double as countless sodium ions as sulfide ions. This ar will teach you just how to uncover the correct ratio of ions, so that you deserve to write a exactly formula.

If you recognize the surname of a binary ionic compound, you have the right to write that is tennis2007.orgical formula. Begin by creating the steel ion with its charge, complied with by the nonmetal ion v its charge. Due to the fact that the all at once compound have to be electrically neutral, decide how numerous of every ion is required in order because that the hopeful and negative charges to cancel each various other out.

Example (PageIndex1): Aluminum Nitride and Lithium Oxide

Write the formulas because that aluminum nitride and lithium oxide.

Solution

Write the formula for aluminum nitrideWrite the formula for lithium oxide
1. Compose the symbol and charge the the cation (metal) very first and the anion (nonmetal) second. (ceAl^3+ : : : : : ceN^3-) (ceLi^+ : : : : : ceO^2-)
2. Use a multiplier to make the complete charge of the cations and also anions equal to every other.

total charge of cations = complete charge that anions

1(3+) = 1(3-)

+3 = -3

total charge of cations = full charge of anions

2(1+) = 1(2-)

+2 = -2

3. Usage the multipliers as subscript for each ion. (ceAl_1N_1) (ceLi_2O_1)
4. Compose the last formula. Leave the end all charges and also all subscripts that room 1. (ceAlN) (ceLi_2O)

An alternative method to composing a exactly formula for an ionic compound is to usage the crisscross method. In this method, the numerical worth of every of the ion dues is crossed end to become the subscript of the various other ion. Indicators of the charges room dropped.

Example (PageIndex2): The Crisscross technique for command (IV) Oxide

Write the formula because that lead (IV) oxide.

Solution

Crisscross MethodWrite the formula for lead (IV) oxide
1. Compose the symbol and also charge the the cation (metal) very first and the anion (nonmetal) second. (cePb^4+ : : : : : ceO^2-)
2. Transpose only the variety of the positive charge to become the subscript of the anion and the number just of the an adverse charge to become the subscript the the cation. api/deki/files/80946/5.5.3.PNG?revision=6&size=bestfit&width=160&height=56" />
3. Reduce to the shortest ratio. This action is not necessary.
4. Create the final formula. Leave the end all subscripts that are 1. (ceNa_2S)

Exercise (PageIndex3)

Write the formula for each ionic compound.

## Polyatomic Ions

Some ions consist of groups of atom bonded together and also have an as whole electric charge. Due to the fact that these ion contain an ext than one atom, lock are referred to as polyatomic ions. Polyatomic ions have characteristic formulas, names, and charges that need to be memorized. Because that example, NO3− is the nitrate ion; it has actually one nitrogen atom and also three oxygen atoms and an overall 1− charge. Table (PageIndex1) list the most usual polyatomic ions.

Table (PageIndex1): part Polyatomic ion NameFormula
ammonium ion NH4+
acetate ion C2H3O2− (also written CH3CO2−)
carbonate ion CO32−
chromate ion CrO42−
dichromate ion Cr2O72−
hydrogen lead carbonate ion (bicarbonate ion) HCO3−
cyanide ion CN−
hydroxide ion OH−
nitrate ion NO3−
nitrite ion NO2−
permanganate ion MnO4−
phosphate ion PO43−
hydrogen phosphate ion HPO42−
dihydrogen phosphate ion H2PO4−
sulfate ion SO42−
hydrogen sulfate ion (bisulfate ion) HSO4−
sulfite ion SO32−

The preeminence for building formulas because that ionic compound containing polyatomic ion is the exact same as for formulas containing monatomic (single-atom) ions: the positive and an unfavorable charges should balance. If more than one of a particular polyatomic ion is needed to balance the charge, the entire formula because that the polyatomic ion should be enclosed in parentheses, and the numerical subscript is placed outside the parentheses. This is to show that the subscript uses to the whole polyatomic ion. An example is Ba(NO3)2.

Example (PageIndex4): Calcium Nitrate

Write the formula because that calcium nitrate.

Solution

Crisscross MethodWrite the formula for calcium nitrate
1. Create the symbol and also charge that the cation (metal) first and the anion (nonmetal) second. (ceCa^2+ : : : : : ceNO_3^-)
2. Transpose just the number of the hopeful charge to become the subscript the the anion and also the number just of the an adverse charge to become the subscript that the cation. [Image_Link]https://tennis2007.org/

Exercise (PageIndex5)

Write the tennis2007.orgistry formula for an ionic compound written of every pair the ions.

the magnesium ion and also the carbonate ion the aluminum ion and the acetate ion Answer a: MgCO3 Answer b: Al(CH3COO)3

## Recognizing Ionic Compounds

There space two ways to identify ionic compounds. First, compounds between metal and nonmetal facets are usually ionic. Because that example, CaBr2 has a metallic element (calcium, a group 2 metal) and also a nonmetallic element (bromine, a team 17 nonmetal). Therefore, the is most most likely an ionic compound. (In fact, the is ionic.) In contrast, the compound NO2 consists of two elements that room both nonmetals (nitrogen, from team 15 , and also oxygen, from team 16 . It is not an ionic compound; it belongs to the classification of covalent compounds questioned elsewhere. Also note the this combination of nitrogen and also oxygen has no electric charge specified, so that is not the nitrite ion.

Second, if you acknowledge the formula the a polyatomic ion in a compound, the link is ionic. For example, if you see the formula Ba(NO3)2, you might recognize the “NO3” component as the nitrate ion, NO3−. (Remember that the convention for creating formulas because that ionic link is not to include the ionic charge.) This is a clue the the other part of the formula, Ba, is in reality the Ba2+ ion, v the 2+ fee balancing the overall 2− charge from the two nitrate ions. Thus, this compound is also ionic.

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Exercise (PageIndex6)

Identify each compound as ionic or not ionic.