Learning Objectives

Know how ions form. Discover the characteristic charges that ions have. Construct a appropriate formula for an ionic compound. Generate a proper name because that an ionic compound.

So far, us have questioned elements and also compounds that room electrically neutral. They have actually the same number of electrons as protons, therefore the negative charges that the electrons is well balanced by the confident charges that the protons. However, this is not constantly the case. Electrons can move from one atom come another; once they do, types with in its entirety electric charges room formed. Such species are called ionsA types with an as whole electric charge.. Varieties with all at once positive charges space termed cationsA types with an as whole positive charge., while species with overall an unfavorable charges are dubbed anionsA types with one overall negative charge.. Psychic that ions are created only as soon as electrons relocate from one atom come another; a proton never moves indigenous one atom to another. Compounds created from hopeful and an adverse ions are referred to as ionic compoundsA compound developed from hopeful and an adverse ions..

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Individual atoms can gain or shed electrons. As soon as they do, they come to be monatomic ions. As soon as atoms get or shed electrons, lock usually obtain or shed a characteristic number of electrons and so take on a characteristic overall charge. Table 3.6 "Monatomic ion of assorted Charges" perform some typical ions in terms of how numerous electrons they lose (making cations) or obtain (making anions). There are several things to notice about the ion in Table 3.6 "Monatomic ion of various Charges". First, each element that forms cations is a metal, except for one (hydrogen), while each element that develops anions is a nonmetal. This is actually among the chemistry properties that metals and also nonmetals: steels tend to form cations, when nonmetals tend to kind anions. Second, many atoms type ions the a single characteristic charge. When sodium atoms type ions, castle always kind a 1+ charge, never ever a 2+ or 3+ or also 1− charge. Thus, if girlfriend commit the information in Table 3.6 "Monatomic ion of miscellaneous Charges" come memory, you will constantly know what charges most atoms form. (In thing 9 "Chemical Bonds", us will comment on why atoms type the charges castle do.)

Table 3.6 Monatomic ion of assorted Charges

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

Third, there are some exception to the vault point. A couple of elements, every metals, can kind more than one feasible charge. For example, iron atom can type 2+ cations or 3+ cations. Cobalt is another element that can kind more 보다 one feasible charged ion (2+ and 3+), while lead can type 2+ or 4+ cations. Unfortunately, there is small understanding which two charges a steel atom may take, so the is ideal to just memorize the feasible charges a certain element have the right to have.

Note the convention because that indicating an ion. The size of the charge is noted as a appropriate superscript beside the prize of the element. If the fee is a solitary positive or an adverse one, the number 1 is not written; if the magnitude of the fee is greater than 1, climate the number is composed before the + or − sign. An element symbol without a charge written beside it is suspect to it is in the uncharged atom.

Naming an ion is straightforward. For a cation, just use the surname of the element and add the native ion (or if you want to be an ext specific, add cation) after ~ the element’s name. Therefore Na+ is the sodium ion; Ca2+ is the calcium ion. If the element has more than one feasible charge, the value of the charge comes after the facet name and also before the word ion. Thus, Fe2+ is the iron 2 ion, when Fe3+ is the iron 3 ion. In print, we usage roman numerals in parentheses to represent the fee on the ion, so these 2 iron ions would certainly be stood for as the iron(II) cation and the iron(III) cation, respectively.

For a monatomic anion, usage the stem of the element name and also append the suffix -ide come it, and also then include ion. This is similar to how we called molecular compounds. Thus, Cl− is the chloride ion, and N3− is the nitride ion.

Example 6

Name every species.

O2− Co Co2+


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

Test Yourself

Name every species.

P3− Sr2+


the phosphide anion the strontium cation

Chemical formulas for ionic compounds are referred to as ionic formulasThe chemistry formula because that an ionic compound.. A proper ionic formula has actually a cation and an anion in it; an ionic link is never formed in between two cations only or two anions only. The an essential to writing suitable ionic recipe is simple: the total positive charge need to balance the total negative charge. Because the dues on the ions room characteristic, periodically we have to have an ext than among a cation or an anion come balance the all at once positive and an adverse charges. That is typical to use the lowest proportion of ions that are required to balance the charges.

For example, take into consideration the ionic compound in between Na+ and also Cl−. Every ion has a solitary charge, one positive and one negative, for this reason we require only one ion of each to balance the all at once charge. When writing the ionic formula, we follow two extr conventions: (1) create the formula for the cation an initial and the formula for the anion next, however (2) carry out not create the dues on the ions. Thus, for the compound in between Na+ and also Cl−, we have actually the ionic formula NaCl (Figure 3.5 "NaCl = Table Salt"). The formula Na2Cl2 additionally has well balanced charges, but the convention is to use the lowest ratio of ions, which would be among each. (Remember from our conventions for composing formulas that us don’t create a 1 subscript if over there is only one atom of a particular element present.) for the ionic compound in between magnesium cations (Mg2+) and also oxide anions (O2−), again we need only one of each ion to balance the charges. By convention, the formula is MgO.

For the ionic compound between Mg2+ ions and Cl− ions, us now consider the reality that the fees have various magnitudes, 2+ on the magnesium ion and 1− top top the chloride ion. To balance the charges through the lowest number of ions possible, we require to have two chloride ion to balance the charge on the one magnesium ion. Fairly than write the formula MgClCl, we combine the 2 chloride ions and write it through a 2 subscript: MgCl2.

What is the formula MgCl2 telling us? There are two chloride ions in the formula. Although chlorine as an facet is a diatomic molecule, Cl2, element chlorine is not component of this ionic compound. The chlorine is in the type of a negatively charged ion, not the neutral element. The 2 subscript is in the ionic formula due to the fact that we require two Cl− ion to balance the charge on one Mg2+ ion.

Example 7

Write the appropriate ionic formula for each that the two provided ions.

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


We require two Cl− ion to balance the charge on one Ca2+ ion, so the appropriate ionic formula is CaCl2. We require three F− ions to balance the charge on the Al3+ ion, so the suitable ionic formula is AlF3. With Al3+ and O2−, note that neither charge is a perfect many of the other. This method we need to go come a least common multiple, i m sorry in this situation will it is in six. To acquire a total of 6+, we require two Al3+ ions; to get 6−, we need three O2− ions. Therefore the appropriate ionic formula is Al2O3.

Test Yourself

Write the suitable ionic formulas for each the the two provided ions.

Fe2+ and S2− Fe3+ and S2−


FeS Fe2S3

Naming ionic compounds is simple: incorporate the name of the cation and also the surname of the anion, in both instances omitting the word ion. Do not use numerical prefixes if there is an ext than one ion vital to balance the charges. NaCl is sodium chloride, a combination of the name of the cation (sodium) and also the anion (chloride). MgO is magnesium oxide. MgCl2 is magnesium chloride—not magnesium dichloride.

In naming ionic compounds who cations deserve to have an ext than one feasible charge, us must also include the charge, in parentheses and in roman inn numerals, as part of the name. For this reason FeS is iron(II) sulfide, when Fe2S3 is iron(III) sulfide. Again, no number prefixes appear in the name. The variety of ions in the formula is dictated through the should balance the positive and an unfavorable charges.

Example 8

Name every ionic compound.

CaCl2 AlF3 Co2O3


making use of the names of the ions, this ionic compound is called calcium chloride. It is not calcium(II) chloride because calcium forms only one cation as soon as it develops an ion, and it has actually a characteristic fee of 2+. The surname of this ionic compound is aluminum fluoride. We recognize that cobalt can have an ext than one possible charge; we just need to determine what that is. Oxide constantly has a 2− charge, therefore with three oxide ions, we have actually a total an adverse charge the 6−. This way that the 2 cobalt ions have to add 6+, i m sorry for 2 cobalt ions way that each one is 3+. Therefore, the appropriate name because that this ionic link is cobalt(III) oxide.

Test Yourself

Name each ionic compound.

Sc2O3 AgCl


scandium oxide silver chloride

How perform you understand whether a formula—and by extension, a name—is because that a molecular link or because that an ionic compound? molecular compounds type between nonmetals and nonmetals, if ionic compounds type between metals and also nonmetals. The periodic table (Figure 3.2 "A basic Periodic Table") deserve to be used to determine which elements are metals and nonmetals.

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

Table 3.7 common Polyatomic Ions

surname Formula and also Charge   surname Formula and also 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 that contain polyatomic ions complies with the exact same rules as the specify name for various other ionic compounds: simply incorporate the name of the cation and also the surname of the anion. Carry out not usage numerical prefixes in the name if over there is an ext than one polyatomic ion; the only exemption to this is if the name of the ion itself includes a number prefix, such together dichromate or triiodide.

Writing the recipe of ionic compounds has actually one important difference. If an ext than one polyatomic ion is necessary to balance the as whole charge in the formula, enclose the formula the the polyatomic ion in parentheses and write the suitable numerical subscript come the right and outside the parentheses. Thus, the formula in between calcium ions, Ca2+, and nitrate ions, NO3−, is appropriately written Ca(NO3)2, not CaNO32 or CaN2O6. Use parentheses where required. The name of this ionic link is merely calcium nitrate.

Example 9

Write the proper formula and also give the ideal name because that each ionic link formed between the two listed ions.

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


because the ammonium ion has actually a 1+ charge and also the sulfide ion has a 2− charge, we need two ammonium ion to balance the charge on a single sulfide ion. Enclosing the formula for the ammonium ion in parentheses, we have (NH4)2S. The compound’s surname is ammonium sulfide. Since the ions have the exact same magnitude the charge, we require only among each to balance the charges. The formula is AlPO4, and the surname of the compound is aluminum phosphate. Neither charge is specific multiple that the other, for this reason we need to go come the least usual multiple the 6. To get 6+, we need three iron(II) ions, and also to obtain 6−, we need two phosphate ions. The suitable formula is Fe3(PO4)2, and the compound’s name is iron(II) phosphate.

Test Yourself

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

NH4+ and also PO43− Co3+ and NO2−


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

Food and also Drink App: salt in your Food

The facet sodium, at the very least in that is ionic kind as Na+, is a important nutrient for humans to live. In fact, the human being body is roughly 0.15% sodium, v the mean person having one-twentieth to one-tenth of a kilogram in their body at any given time, mainly in fluids exterior cells and also in other bodily fluids.

Sodium is also present in our diet. The typical table salt we use on our foods items is an ionic sodium compound. Countless processed foods likewise contain significant amounts that sodium included to them together a selection of ionic compounds. Why are sodium compounds used so much? usually sodium compounds are inexpensive, but, an ext importantly, most ionic sodium compounds dissolve easily. This permits processed food manufacturers to include sodium-containing substances to food mixtures and also know the the compound will dissolve and distribute evenly throughout the food. Basic ionic compounds together as sodium nitrite (NaNO2) are included to cured meats, such as bacon and deli-style meats, while a compound called sodium benzoate is added to many packaged foods items as a preservative. Table 3.8 "Some salt Compounds added to Food" is a partial list of some sodium additives supplied in food. Several of them you might recognize after reading this chapter. Rather you may not recognize, however they space all ionic sodium compounds through some negatively fee ion additionally present.

Table 3.8 part Sodium Compounds added to Food

salt Compound use in Food
Sodium acetate preservative, acidity 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, acidity 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, shade fixative
Sodium orthophenyl phenol preservative
Sodium propionate preservative
Sodium propyl para-hydroxybenzoate preservative
Sodium sorbate preservative
Sodium stearoyl lactylate emulsifier
Sodium succinates acidity regulator, smell enhancer
Sodium salt 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 countless sodium compounds in prepared and processed foodstuffs has alarmed some physicians and nutritionists. They argue that the average human being consumes too much sodium native his or she diet. The average human being needs only about 500 mg of sodium every day; most world consume more than this—up come 10 times as much. Part studies have actually implicated enhanced sodium intake with high blood pressure; more recent studies indicate that the connect is questionable. However, there has been a press to alleviate the amount of sodium most people ingest every day: avoid processed and manufactured foods, read labels on packaged foodstuffs (which include an clues of the salt content), don’t oversalt foods, and also use other herbs and also spices besides salt in cooking.


Food labels incorporate the amount of sodium per serving. This details label mirrors that there room 75 mg of sodium in one offer of this particular food item.

Key Takeaways

Ions kind when atoms shed or acquire electrons. Ionic compounds have positive ion and negative ions. Ionic recipe balance the total positive and an adverse charges. Ionic compounds have actually a straightforward system of naming. Teams of atoms can have an all at once charge and make ionic compounds.


Explain just how cations form.

Explain how anions form.

Give the charge each atom takes once it forms an ion. If more than one charge is possible, list both.

K O Co

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

Ca i Fe

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

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Ag Au Br

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