Learning Objectives

Know just how ions form. Discover the characteristic fees that ion have. Construct a suitable formula for an ionic compound. Create a appropriate name for an ionic compound.

So far, us have discussed elements and also compounds that are electrically neutral. They have actually the same number of electrons together protons, for this reason the an adverse charges of the electrons is well balanced by the positive charges that the protons. However, this is not always the case. Electrons have the right to move from one atom to another; as soon as they do, varieties with as whole electric charges space formed. Such species are dubbed ionsA types with an as whole electric charge.. Species with as whole positive charges room termed cationsA types with an all at once positive charge., while species with overall an adverse charges are referred to as anionsA varieties with one overall negative charge.. Mental that ion are created only when electrons move from one atom come another; a proton never moves native one atom come another. Compounds developed from positive and negative ions are dubbed ionic compoundsA compound developed from positive and negative ions..

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Individual atoms can obtain or shed electrons. As soon as they do, they end up being monatomic ions. As soon as atoms get or lose electrons, they usually gain or lose a characteristic number of electrons and so take on a characteristic in its entirety charge. Table 3.6 "Monatomic ions of miscellaneous Charges" lists some usual ions in regards to how countless electrons they shed (making cations) or get (making anions). There are several things to notice about the ions in Table 3.6 "Monatomic ion of assorted Charges". First, each facet that develops cations is a metal, other than for one (hydrogen), while each element that forms anions is a nonmetal. This is actually among the chemical properties of metals and nonmetals: metals tend to type cations, when nonmetals often tend to type anions. Second, most atoms kind ions of a single characteristic charge. Once sodium atoms type ions, they always type a 1+ charge, never a 2+ or 3+ or also 1− charge. Thus, if friend commit the info in Table 3.6 "Monatomic ion of miscellaneous Charges" to memory, you will constantly know what charges many atoms form. (In chapter 9 "Chemical Bonds", we will discuss why atoms form the charges they do.)

Table 3.6 Monatomic ions of assorted Charges

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

Third, there space some exception to the vault point. A few elements, every metals, can kind more than one feasible charge. For example, iron atom can kind 2+ cations or 3+ cations. Cobalt is an additional element the can type more than one possible charged ion (2+ and 3+), while command can kind 2+ or 4+ cations. Unfortunately, over there is little understanding which two charges a steel atom may take, so that is ideal to simply memorize the feasible charges a particular element deserve to have.

Note the convention for indicating one ion. The size of the fee is listed as a appropriate superscript alongside the prize of the element. If the charge is a single positive or an adverse one, the number 1 is no written; if the size of the fee is higher than 1, climate the number is composed before the + or − sign. An element symbol without a charge written beside it is assumed to be the uncharged atom.

Naming an ion is straightforward. For a cation, simply use the surname of the facet and add the native ion (or if you desire to be an ext specific, include cation) after ~ the element’s name. So Na+ is the sodium ion; Ca2+ is the calcium ion. If the aspect has an ext 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, while Fe3+ is the iron 3 ion. In print, we use roman numerals in clip to stand for the fee on the ion, therefore these 2 iron ions would certainly be stood for as the iron(II) cation and also the iron(III) cation, respectively.

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

Example 6

Name every species.

O2− Co Co2+


This species has a 2− charge on it, so that is an anion. Anions are called using the stem the the aspect name through the suffix -ide added. This is the oxide anion. Due to the fact that this types has no charge, the is one atom in its element form. This is cobalt.

Test Yourself

Name each species.

P3− Sr2+


the phosphide anion the strontium cation

Chemical formulas for ionic link are referred to as ionic formulasThe chemistry formula for an ionic compound.. A proper ionic formula has a cation and an anion in it; an ionic link is never formed between two cations just or two anions only. The vital to writing suitable ionic recipe is simple: the total positive charge must balance the total an unfavorable charge. Since the dues on the ions are characteristic, periodically we have to have more than among a cation or one anion to balance the overall positive and negative charges. It is typical to use the lowest proportion of ion that are essential to balance the charges.

For example, think about the ionic compound in between Na+ and Cl−. Every ion has a single charge, one positive and one negative, so we need only one ion of every to balance the as whole charge. When writing the ionic formula, we follow two extr conventions: (1) create the formula because that the cation very first and the formula for the anion next, yet (2) do not write the charges on the ions. Thus, because that the compound in between Na+ and Cl−, we have actually the ionic formula NaCl (Figure 3.5 "NaCl = Table Salt"). The formula Na2Cl2 likewise has balanced charges, yet the convention is to usage the lowest proportion of ions, which would be among each. (Remember from ours conventions for creating formulas that us don’t create a 1 subscript if over there is just one atom of a certain element present.) because that the ionic compound in between magnesium cations (Mg2+) and oxide anions (O2−), again we require only one of each ion come balance the charges. Through convention, the formula is MgO.

For the ionic compound between Mg2+ ions and Cl− ions, us now think about the truth that the fees have various magnitudes, 2+ on the magnesium ion and also 1− on the chloride ion. To balance the charges with the lowest number of ions possible, we need to have actually two chloride ions to balance the fee on the one magnesium ion. Fairly than create the formula MgClCl, we incorporate 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. Back chlorine together an aspect is a diatomic molecule, Cl2, elemental chlorine is not component of this ionic compound. The chlorine is in the kind of a negatively charged ion, not the neutral element. The 2 subscript is in the ionic formula because we require two Cl− ion to balance the fee on one Mg2+ ion.

Example 7

Write the suitable ionic formula because that each the the two provided ions.

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


We need two Cl− ions to balance the fee on one Ca2+ ion, for this reason the ideal ionic formula is CaCl2. We need three F− ion to balance the fee on the Al3+ ion, for this reason the ideal ionic formula is AlF3. V Al3+ and O2−, note that neither fee is a perfect multiple of the other. This method we need to go come a least common multiple, i beg your pardon in this instance will it is in six. To obtain a full of 6+, we need two Al3+ ions; to acquire 6−, we require three O2− ions. Thus the suitable ionic formula is Al2O3.

Test Yourself

Write the appropriate ionic formulas because that each the the two offered ions.

Fe2+ and also S2− Fe3+ and also S2−


FeS Fe2S3

Naming ionic compounds is simple: combine the name of the cation and also the name of the anion, in both cases omitting words ion. Do not use numerical prefixes if there is more than one ion necessary to balance the charges. NaCl is sodium chloride, a mix 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 whose cations can have more than one possible charge, we must also include the charge, in parentheses and also in roman numerals, as part of the name. Therefore FeS is iron(II) sulfide, while Fe2S3 is iron(III) sulfide. Again, no number prefixes appear in the name. The variety of ions in the formula is dictated through the need to balance the hopeful and an unfavorable charges.

Example 8

Name every ionic compound.

CaCl2 AlF3 Co2O3


making use of the surname of the ions, this ionic compound is named calcium chloride. It is not calcium(II) chloride since calcium creates only one cation once it develops an ion, and also it has a characteristic fee of 2+. The name of this ionic link is aluminum fluoride. We know that cobalt have the right to have an ext than one possible charge; we just need to determine what the is. Oxide always has a 2− charge, for this reason with three oxide ions, we have actually a total negative charge that 6−. This method that the two cobalt ions have actually to add 6+, i beg your pardon for two cobalt ions way that each one is 3+. Therefore, the appropriate name for this ionic compound is cobalt(III) oxide.

Test Yourself

Name each ionic compound.

Sc2O3 AgCl


scandium oxide silver chloride

How execute you know whether a formula—and by extension, a name—is because that a molecular compound or for an ionic compound? molecule compounds type between nonmetals and also nonmetals, when ionic compounds form between metals and nonmetals. The regular table (Figure 3.2 "A an easy Periodic Table") have the right to be supplied to recognize which elements are metals and also nonmetals.

There also exists a team of ions that contain much more than one atom. This are dubbed polyatomic ionsAn ion the contains more than one atom.. Table 3.7 "Common Polyatomic Ions" perform the formulas, charges, and also names of some typical polyatomic ions. Only one of them, the ammonium ion, is a cation; the rest are anions. Many of them additionally contain oxygen atoms, so occasionally they are referred to as oxyanions. Few of them, such as nitrate and also nitrite, and also sulfate and also sulfite, have very comparable formulas and also names, so care must it is in taken to acquire the formulas and names correct. Keep in mind that the -ite polyatomic ion has one much less oxygen atom in that formula 보다 the -ate ion yet with the exact same ionic charge.

Table 3.7 typical Polyatomic Ions

name Formula and 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 specify name of ionic compounds the contain polyatomic ions follows the same rules as the naming for various other ionic compounds: simply incorporate the surname of the cation and the name of the anion. Perform not use numerical prefixes in the surname if over there is an ext than one polyatomic ion; the only exception to this is if the name of the ion itself consists of a number prefix, such as dichromate or triiodide.

Writing the formulas of ionic compounds has one vital difference. If more than one polyatomic ion is necessary to balance the as whole charge in the formula, enclose the formula of the polyatomic ion in parentheses and also write the ideal numerical subscript to the right and outside the parentheses. Thus, the formula in between calcium ions, Ca2+, and nitrate ions, NO3−, is effectively written Ca(NO3)2, not CaNO32 or CaN2O6. Usage parentheses where required. The surname of this ionic compound is just calcium nitrate.

Example 9

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

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


due to the fact that the ammonium ion has actually a 1+ charge and also the sulfide ion has actually a 2− charge, we need two ammonium ion to balance the fee 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. Because the ions have the same magnitude the charge, we need only one of each come balance the charges. The formula is AlPO4, and the name of the link is aluminum phosphate. Neither fee is specific multiple of the other, so we need to go to the least usual multiple of 6. To get 6+, we require three iron(II) ions, and to get 6−, we need two phosphate ions. The ideal formula is Fe3(PO4)2, and the compound’s surname is iron(II) phosphate.

Test Yourself

Write the ideal formula and also give the appropriate name because that each ionic link formed in between the two noted ions.

NH4+ and also PO43− Co3+ and also NO2−


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

Food and Drink App: sodium in her Food

The facet sodium, at least in that is ionic form as Na+, is a vital nutrient for humans to live. In fact, the human body is approximately 0.15% sodium, through the median person having actually one-twentieth to one-tenth of a kilogram in your body at any type of given time, mostly in fluids outside cells and in various other bodily fluids.

Sodium is additionally present in our diet. The common table salt we use on our foodstuffs is one ionic sodium compound. Countless processed foods additionally contain significant amounts that sodium included to them as a selection of ionic compounds. Why are sodium compounds offered so much? usually sodium compounds are inexpensive, but, more importantly, most ionic sodium compounds dissolve easily. This enables processed food manufacturers to include sodium-containing substances to food mixtures and know that the compound will dissolve and also distribute same throughout the food. Simple ionic compounds such as salt nitrite (NaNO2) are included to cured meats, such together bacon and deli-style meats, when a compound referred to as sodium benzoate is added to plenty of packaged foods as a preservative. Table 3.8 "Some salt Compounds added to Food" is a partial list of some sodium additives supplied in food. Few of them you may recognize after analysis this chapter. Others you might not recognize, but they room all ionic salt compounds v some negatively charged ion likewise present.

Table 3.8 some Sodium Compounds included to Food

salt Compound usage 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, 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, 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 usage of so plenty of sodium compounds in prepared and also processed foods items has alarmed some physicians and nutritionists. They argue that the average human being consumes too lot sodium native his or she diet. The average human being needs only around 500 mg of sodium every day; most people consume an ext than this—up to 10 times as much. Part studies have actually implicated boosted sodium intake through high blood pressure; newer studies suggest that the attach is questionable. However, there has actually been a push to reduce the quantity of sodium most civilization ingest every day: stop processed and manufactured foods, review labels top top packaged foods (which incorporate an clues of the salt content), don’t oversalt foods, and also use other herbs and spices besides salt in cooking.


Food labels include the lot of sodium per serving. This particular label mirrors that there room 75 mg of sodium in one serving of this certain food item.

Key Takeaways

Ions form when atoms shed or obtain electrons. Ionic compounds have actually positive ion and an adverse ions. Ionic formulas balance the full positive and an unfavorable charges. Ionic compounds have a simple system that naming. Teams of atoms have the right to have an overall charge and make ionic compounds.


Explain exactly how cations form.

Explain exactly how anions form.

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

K O Co

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

Ca i Fe

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

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Ag Au Br

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