Learning Objectives

Know exactly how ions form. Find out the characteristic fees that ion have. Build a ideal formula because that an ionic compound. Generate a proper name for an ionic compound.

So far, we have disputed elements and also compounds that are electrically neutral. They have the same variety of electrons together protons, for this reason the negative charges that the electron is well balanced by the confident charges the the protons. However, this is not always the case. Electrons have the right to move native one atom to another; once they do, types with as whole electric charges space formed. Such types are dubbed ionsA species with an in its entirety electric charge.. Types with in its entirety positive charges room termed cationsA species with an in its entirety positive charge., while types with overall negative charges are called anionsA species with one overall an adverse charge.. Remember that ion are formed only as soon as electrons move from one atom to another; a proton never moves native one atom come another. Compounds created from hopeful and an adverse ions are dubbed ionic compoundsA compound formed from confident and an unfavorable ions..

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Individual atom can gain or shed electrons. As soon as they do, they end up being monatomic ions. Once atoms obtain or shed electrons, lock usually obtain or lose a characteristic variety of electrons and so take on a characteristic overall charge. Table 3.6 "Monatomic ion of miscellaneous Charges" perform some usual ions in terms of how countless electrons they shed (making cations) or obtain (making anions). There are number of things to an alert about the ion in Table 3.6 "Monatomic ion of assorted Charges". First, each aspect that develops cations is a metal, except for one (hydrogen), when each element that creates anions is a nonmetal. This is actually among the chemical properties of metals and nonmetals: metals tend to kind cations, if nonmetals tend to kind anions. Second, most atoms type ions of a single characteristic charge. Once sodium atoms type ions, castle always form a 1+ charge, never a 2+ or 3+ or also 1− charge. Thus, if girlfriend commit the details in Table 3.6 "Monatomic ion of various Charges" come memory, you will always know what charges many atoms form. (In chapter 9 "Chemical Bonds", us will discuss why atoms form the charges lock do.)

Table 3.6 Monatomic ions of miscellaneous Charges

Ions developed by losing a single electron H+
Ions formed by losing two electrons Mg2+
Ions created by shedding three electrons Sc3+
Ions developed by losing 4 electrons Ti4+
Ions formed by getting a single electron F−
Ions developed by obtaining two electrons O2−
Ions developed by getting three electrons N3−

Third, there are some exception to the previous point. A couple of elements, every metals, can form more than one possible charge. For example, iron atoms can type 2+ cations or 3+ cations. Cobalt is an additional element the can form more 보다 one feasible charged ion (2+ and 3+), while lead can kind 2+ or 4+ cations. Unfortunately, there is little understanding which 2 charges a steel atom might take, so the is ideal to just memorize the possible charges a specific element deserve to have.

Note the convention because that indicating an ion. The size of the fee is noted as a best superscript beside the symbol of the element. If the charge is a solitary positive or an unfavorable one, the number 1 is no written; if the magnitude of the fee is greater than 1, climate the number is created before the + or − sign. An aspect symbol without a charge written alongside it is suspect to be the uncharged atom.

Naming an ion is straightforward. Because that a cation, simply use the name of the aspect and include the indigenous ion (or if you want to be more specific, add cation) ~ the element’s name. So Na+ is the sodium ion; Ca2+ is the calcium ion. If the facet has much more than one possible charge, the value of the fee comes after the aspect name and also before words ion. Thus, Fe2+ is the iron two ion, when Fe3+ is the iron three ion. In print, we usage roman number in bracket to stand for the fee on the ion, for this reason these 2 iron ions would be stood for as the iron(II) cation and the iron(III) cation, respectively.

For a monatomic anion, usage the stem that the aspect name and append the suffix -ide come it, and then add ion. This is comparable to exactly how we named molecular compounds. Thus, Cl− is the chloride ion, and also N3− is the nitride ion.

Example 6

Name every species.

O2− Co Co2+


This varieties has a 2− charge on it, so that is one anion. Anions are called using the stem the the aspect name v the suffix -ide added. This is the oxide anion. Since this species has no charge, that is an atom in its elemental form. This is cobalt.

Test Yourself

Name each species.

P3− Sr2+


the phosphide anion the strontium cation

Chemical formulas because that ionic compound are dubbed ionic formulasThe chemical formula because that an ionic compound.. A proper ionic formula has actually a cation and also an anion in it; one ionic link is never ever formed between two cations just or 2 anions only. The key to writing suitable ionic formulas is simple: the complete positive charge should balance the total negative charge. Because the charges on the ions room characteristic, occasionally we have to have much more than among a cation or one anion come balance the all at once positive and negative charges. The is traditional to usage the lowest ratio of ion that are necessary to balance the charges.

For example, think about the ionic compound in between Na+ and also Cl−. Each ion has actually a solitary charge, one positive and one negative, so we need only one ion of each to balance the all at once charge. Once writing the ionic formula, we follow two added conventions: (1) compose the formula for the cation very first and the formula because that the anion next, yet (2) do not create the fees on the ions. Thus, for the compound between Na+ and also Cl−, we have the ionic formula NaCl (Figure 3.5 "NaCl = Table Salt"). The formula Na2Cl2 additionally has well balanced charges, yet the convention is to usage the lowest ratio of ions, which would certainly be one of each. (Remember from our conventions for composing formulas that we don’t write a 1 subscript if there is just one atom that a details element present.) for the ionic compound in between magnesium cations (Mg2+) and oxide anions (O2−), again we need only one of each ion to balance the charges. Through convention, the formula is MgO.

For the ionic compound in between Mg2+ ions and also Cl− ions, us now consider the reality that the fees have various magnitudes, 2+ on the magnesium ion and 1− ~ above the chloride ion. Come balance the charges v the lowest variety of ions possible, we need to have actually two chloride ions to balance the charge on the one magnesium ion. Rather than create the formula MgClCl, we integrate the two chloride ions and write it with a 2 subscript: MgCl2.

What is the formula MgCl2 telling us? There are two chloride ion in the formula. Return chlorine together an element is a diatomic molecule, Cl2, element chlorine is not component of this ionic compound. The chlorine is in the form of a negatively fee ion, not the neutral element. The 2 subscript is in the ionic formula since we need two Cl− ions to balance the charge on one Mg2+ ion.

Example 7

Write the ideal ionic formula because that each that the two given ions.

Ca2+ and Cl− Al3+ and also F− Al3+ and O2−


We require two Cl− ions to balance the charge on one Ca2+ ion, therefore the proper ionic formula is CaCl2. We require three F− ion to balance the charge on the Al3+ ion, therefore the suitable ionic formula is AlF3. Through Al3+ and O2−, keep in mind that neither charge is a perfect lot of of the other. This means we need to go come a least typical multiple, i m sorry in this situation will it is in six. To gain a total of 6+, we need two Al3+ ions; to get 6−, we need three O2− ions. For this reason the ideal ionic formula is Al2O3.

Test Yourself

Write the proper ionic formulas for each that the two given ions.

Fe2+ and also S2− Fe3+ and S2−


FeS Fe2S3

Naming ionic link is simple: incorporate the name of the cation and also the surname of the anion, in both instances omitting words ion. Do not usage numerical prefixes if over there is more than one ion crucial to balance the charges. NaCl is sodium chloride, a mix of the surname of the cation (sodium) and the anion (chloride). MgO is magnesium oxide. MgCl2 is magnesium chloride—not magnesium dichloride.

In naming ionic compounds whose cations can have more than one possible charge, us must likewise include the charge, in parentheses and also in roman inn numerals, as component of the name. Therefore FeS is iron(II) sulfide, when Fe2S3 is iron(III) sulfide. Again, no numerical prefixes appear in the name. The variety of ions in the formula is dictated by the must balance the optimistic and an adverse charges.

Example 8

Name every ionic compound.

CaCl2 AlF3 Co2O3


using the name of the ions, this ionic link is called calcium chloride. It is no calcium(II) chloride because calcium develops only one cation once it creates an ion, and also it has a characteristic charge of 2+. The surname of this ionic compound is aluminum fluoride. We know that cobalt deserve to have an ext than one possible charge; we simply need to determine what the is. Oxide constantly has a 2− charge, therefore with 3 oxide ions, we have actually a total an adverse charge of 6−. This method that the 2 cobalt ions have actually to contribute 6+, i m sorry for 2 cobalt ions method that each one is 3+. Therefore, the ideal name because that this ionic compound is cobalt(III) oxide.

Test Yourself

Name every ionic compound.

Sc2O3 AgCl


scandium oxide silver chloride

How do you know whether a formula—and by extension, a name—is for a molecular compound or for an ionic compound? molecular compounds type between nonmetals and nonmetals, while ionic compounds kind between metals and also nonmetals. The routine table (Figure 3.2 "A straightforward Periodic Table") can be used to identify which elements are metals and also nonmetals.

There additionally exists a group of ion that contain much more than one atom. These are called polyatomic ionsAn ion the contains an ext than one atom.. Table 3.7 "Common Polyatomic Ions" lists the formulas, charges, and also names that some usual polyatomic ions. Only among them, the ammonium ion, is a cation; the rest are anions. Most of them likewise contain oxygen atoms, so occasionally they are described as oxyanions. Several of them, such together nitrate and also nitrite, and also sulfate and also sulfite, have actually very similar formulas and also names, so care must be taken to gain the formulas and also names correct. Note that the -ite polyatomic ion has one much less oxygen atom in its formula 보다 the -ate ion yet with the exact same ionic charge.

Table 3.7 common Polyatomic Ions

name Formula and Charge   name Formula and Charge
ammonium NH4+   hydroxide OH−
acetate C2H3O2−, or CH3COO− nitrate NO3−
bicarbonate (hydrogen carbonate) HCO3− nitrite NO2−
bisulfate (hydrogen sulfate) HSO4− peroxide O22−
carbonate CO32− perchlorate ClO4−
chlorate ClO3− phosphate PO43−
chromate CrO42− sulfate SO42−
cyanide CN− sulfite SO32−
dichromate Cr2O72− triiodide I3−

The naming of ionic compounds the contain polyatomic ions adheres to the exact same rules together the naming for various other ionic compounds: simply incorporate the name of the cation and the name of the anion. Perform not usage numerical prefixes in the name if over there is more than one polyatomic ion; the only exception to this is if the surname of the ion itself contains a number prefix, such together dichromate or triiodide.

Writing the formulas of ionic compounds has actually one important difference. If more than one polyatomic ion is required to balance the overall charge in the formula, enclose the formula that the polyatomic ion in parentheses and also write the appropriate numerical subscript come the right and outside the parentheses. Thus, the formula between calcium ions, Ca2+, and nitrate ions, NO3−, is correctly written Ca(NO3)2, no CaNO32 or CaN2O6. Use parentheses wherein required. The name of this ionic link is merely calcium nitrate.

Example 9

Write the proper formula and also give the proper name for each ionic compound formed between the two provided ions.

NH4+ and also S2− Al3+ and PO43− Fe2+ and also PO43−


since the ammonium ion has actually a 1+ charge and the sulfide ion has a 2− charge, we require two ammonium ions to balance the charge on a solitary sulfide ion. Enclosing the formula because that the ammonium ion in parentheses, we have actually (NH4)2S. The compound’s name is ammonium sulfide. Since the ions have actually the same magnitude that charge, we require only one of each come balance the charges. The formula is AlPO4, and also the surname of the link is aluminum phosphate. Neither charge is specific multiple the the other, therefore we have to go come the least common multiple that 6. To acquire 6+, we require three iron(II) ions, and to acquire 6−, we require two phosphate ions. The ideal formula is Fe3(PO4)2, and also the compound’s surname is iron(II) phosphate.

Test Yourself

Write the appropriate formula and give the appropriate name because that each ionic compound formed between the two provided ions.

NH4+ and PO43− Co3+ and NO2−


(NH4)3PO4, ammonium phosphate Co(NO2)3, cobalt(III) nitrite

Food and Drink App: salt in her Food

The aspect sodium, at the very least in that is ionic type as Na+, is a essential nutrient for human beings to live. In fact, the human body is about 0.15% sodium, v the typical person having actually one-twentieth to one-tenth the a kilogram in their body at any type of given time, largely in fluids exterior cells and also in various other bodily fluids.

Sodium is likewise present in our diet. The typical table salt we use on our foods items is one ionic sodium compound. Numerous processed foods also contain significant amounts of sodium included to them together a range of ionic compounds. Why are sodium compounds used so much? usually sodium compounds space inexpensive, but, much more importantly, many ionic salt compounds dissolve easily. This allows processed food manufacturers to add sodium-containing substances to food mixtures and know that the compound will dissolve and distribute same throughout the food. Basic ionic compounds together as sodium nitrite (NaNO2) are added to cured meats, such as bacon and also deli-style meats, if a compound referred to as sodium benzoate is included to plenty of packaged foods as a preservative. Table 3.8 "Some salt Compounds added to Food" is a partial perform of some sodium additives supplied in food. Some of them you might recognize after analysis this chapter. Others you might not recognize, however they are all ionic salt compounds through some negatively fee ion additionally present.

Table 3.8 part Sodium Compounds added to Food

salt Compound usage in Food
Sodium acetate preservative, mountain regulator
Sodium adipate food acid
Sodium alginate thickener, vegetable gum, stabilizer, gelling agent, emulsifier
Sodium aluminum phosphate acidity regulator, emulsifier
Sodium aluminosilicate anticaking agent
Sodium ascorbate antioxidant
Sodium benzoate preservative
Sodium bicarbonate mineral salt
Sodium bisulfite preservative, antioxidant
Sodium carbonate mineral salt
Sodium carboxymethylcellulose emulsifier
Sodium citrates food acid
Sodium dehydroacetate preservative
Sodium erythorbate antioxidant
Sodium erythorbin antioxidant
Sodium ethyl para-hydroxybenzoate preservative
Sodium ferrocyanide anticaking agent
Sodium formate preservative
Sodium fumarate food acid
Sodium gluconate stabilizer
Sodium hydrogen acetate preservative, mountain regulator
Sodium hydroxide mineral salt
Sodium lactate food acid
Sodium malate food acid
Sodium metabisulfite preservative, antioxidant, bleaching agent
Sodium methyl para-hydroxybenzoate preservative
Sodium nitrate preservative, color fixative
Sodium nitrite preservative, color fixative
Sodium orthophenyl phenol preservative
Sodium propionate preservative
Sodium propyl para-hydroxybenzoate preservative
Sodium sorbate preservative
Sodium stearoyl lactylate emulsifier
Sodium succinates acidity regulator, odor enhancer
Sodium salts of fat acids emulsifier, stabilizer, anticaking agent
Sodium sulfite mineral salt, preservative, antioxidant
Sodium sulfite preservative, antioxidant
Sodium tartrate food acid
Sodium tetraborate preservative

The use of so many sodium link in prepared and processed foodstuffs has alarmed part physicians and also nutritionists. Castle argue the the average human consumes too lot sodium indigenous his or she diet. The average human being needs only around 500 mg of sodium every day; most human being consume more than this—up come 10 times as much. Some studies have actually implicated increased sodium intake v high blood pressure; more recent studies suggest that the connect is questionable. However, there has been a press to mitigate the lot of salt most human being ingest every day: stop processed and also manufactured foods, read labels on packaged foodstuffs (which incorporate an point out of the sodium content), nothing oversalt foods, and use various other herbs and spices as well as salt in cooking.


Food labels incorporate the quantity of salt per serving. This specific label reflects that there space 75 mg of salt in one offer of this certain food item.

Key Takeaways

Ions form when atoms lose or obtain electrons. Ionic compounds have positive ion and an adverse ions. Ionic recipe balance the full positive and an unfavorable charges. Ionic compounds have actually a simple system the naming. Groups of atoms can have an as whole charge and also make ionic compounds.


Explain just how cations form.

Explain just how anions form.

Give the fee each atom takes once it develops an ion. If an ext than one charge is possible, list both.

K O Co

Give the fee each atom takes as soon as it forms an ion. If more than one fee is possible, list both.

Ca ns Fe

Give the fee each atom takes as soon as it forms an ion. If an ext than one charge is possible, perform both.

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Ag Au Br

Give the fee each atom takes when it develops an ion. If much more than one fee is possible, list both.