Learning Objectives

Know just how ions form. Discover the characteristic fees that ions have. Build a appropriate formula because that an ionic compound. Create a ideal name because that an ionic compound.

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

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Individual atoms can obtain or lose electrons. As soon as they do, they come to be monatomic ions. As soon as atoms get or lose electrons, lock usually get or shed a characteristic variety of electrons and also so take it on a characteristic all at once charge. Table 3.6 "Monatomic ion of various Charges" perform some usual ions in regards to how many electrons they lose (making cations) or obtain (making anions). There are numerous things to notice about the ions in Table 3.6 "Monatomic ion of various Charges". First, each element that develops cations is a metal, other than for one (hydrogen), when each facet that develops anions is a nonmetal. This is actually among the chemistry properties of metals and nonmetals: metals tend to kind cations, when nonmetals tend to form anions. Second, many atoms type ions that a single characteristic charge. Once sodium atoms kind ions, castle always form a 1+ charge, never ever a 2+ or 3+ or even 1− charge. Thus, if friend commit the details in Table 3.6 "Monatomic ions of various Charges" to memory, girlfriend will always know what charges most atoms form. (In thing 9 "Chemical Bonds", us will comment on why atoms form the charges they do.)

Table 3.6 Monatomic ion of assorted Charges

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

Third, there room some exceptions to the previous point. A few elements, every metals, can kind more 보다 one possible charge. Because that example, iron atom can form 2+ cations or 3+ cations. Cobalt is one more element the can type more than one feasible charged ion (2+ and 3+), while lead can form 2+ or 4+ cations. Unfortunately, there is little understanding which two charges a metal atom may take, so the is ideal to just memorize the possible charges a details element can have.

Note the convention because that indicating an ion. The magnitude of the fee is listed as a appropriate superscript next to the prize of the element. If the fee is a single positive or an unfavorable one, the number 1 is not written; if the size of the charge is better than 1, climate the number is composed before the + or − sign. An facet symbol without a charge written next to it is suspect to be the uncharged atom.

Naming an ion is straightforward. For a cation, simply use the surname of the aspect and add the indigenous ion (or if you want to be an ext specific, include cation) after ~ the element’s name. Therefore Na+ is the sodium ion; Ca2+ is the calcium ion. If the aspect has much more than one feasible charge, the worth of the charge comes ~ the aspect name and before the word ion. Thus, Fe2+ is the iron two ion, if Fe3+ is the iron 3 ion. In print, we usage roman number in bracket to represent the fee on the ion, therefore these 2 iron ions would be represented as the iron(II) cation and the iron(III) cation, respectively.

For a monatomic anion, usage the stem the the element name and also append the suffix -ide to it, and also then include ion. This is similar 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 named using the stem of the aspect name v the suffix -ide added. This is the oxide anion. Due to the fact that this species has no charge, that is an atom in its element form. This is cobalt.

Test Yourself

Name every species.

P3− Sr2+


the phosphide anion the strontium cation

Chemical formulas for ionic compounds are dubbed ionic formulasThe chemistry formula for an ionic compound.. A proper ionic formula has a cation and an anion in it; one ionic link is never formed between two cations just or 2 anions only. The key to writing proper ionic formulas is simple: the total positive charge must balance the total an unfavorable charge. Because the charges on the ions space characteristic, sometimes we have to have an ext than one of a cation or one anion to balance the as whole positive and an adverse charges. That is traditional to usage the lowest proportion of ion that are necessary to balance the charges.

For example, consider the ionic compound in between Na+ and also Cl−. Each ion has actually a single charge, one positive and one negative, for this reason we need only one ion of every to balance the as whole charge. Once writing the ionic formula, us follow two added conventions: (1) create the formula for the cation first and the formula for the anion next, yet (2) do not compose 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 also has well balanced charges, however the convention is to usage the lowest ratio of ions, which would certainly be one of each. (Remember from our conventions for creating formulas that us don’t write a 1 subscript if there is only one atom that a certain element present.) because that the ionic compound between magnesium cations (Mg2+) and also oxide anions (O2−), again we require only among each ion come balance the charges. By convention, the formula is MgO.

For the ionic compound between Mg2+ ions and Cl− ions, we now think about the reality that the fees have various magnitudes, 2+ on the magnesium ion and also 1− on the chloride ion. Come balance the charges through 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 compose the formula MgClCl, we integrate the two chloride ions and also write it through a 2 subscript: MgCl2.

What is the formula MgCl2 telling us? There room two chloride ions in the formula. Return chlorine together an facet is a diatomic molecule, Cl2, elemental chlorine is not part of this ionic compound. The chlorine is in the type of a negatively charged ion, no the neutral element. The 2 subscript is in the ionic formula because we require two Cl− ions to balance the charge on one Mg2+ ion.

Example 7

Write the proper ionic formula for each the the two provided ions.

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


We need two Cl− ion to balance the fee on one Ca2+ ion, therefore the proper ionic formula is CaCl2. We need three F− ions to balance the charge on the Al3+ ion, so the ideal ionic formula is AlF3. With Al3+ and also O2−, keep in mind that neither fee is a perfect many of the other. This way we have to go to a least usual multiple, i m sorry in this situation will it is in six. To obtain a full of 6+, we need two Al3+ ions; to obtain 6−, we need three O2− ions. Hence the proper ionic formula is Al2O3.

Test Yourself

Write the suitable ionic formulas because that each of the two provided ions.

Fe2+ and also S2− Fe3+ and also S2−


FeS Fe2S3

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

In specify name ionic compounds who cations deserve to have more than one possible charge, us must also include the charge, in parentheses and also in roman inn numerals, as part of the name. Thus FeS is iron(II) sulfide, if Fe2S3 is iron(III) sulfide. Again, no number prefixes show up in the name. The variety of ions in the formula is dictated by the should balance the positive and an adverse charges.

Example 8

Name each ionic compound.

CaCl2 AlF3 Co2O3


using the surname of the ions, this ionic compound is called calcium chloride. It is not calcium(II) chloride due to the fact that calcium forms only one cation once it develops an ion, and also it has actually a characteristic fee of 2+. The name of this ionic compound is aluminum fluoride. We recognize that cobalt have the right to have more than one feasible charge; we just need to identify what the is. Oxide constantly has a 2− charge, therefore with three oxide ions, we have a total an unfavorable charge the 6−. This method that the two cobalt ions have to add 6+, i beg your pardon for two cobalt ions method that each one is 3+. Therefore, the appropriate name because that this ionic compound is cobalt(III) oxide.

Test Yourself

Name each ionic compound.

Sc2O3 AgCl


scandium oxide silver chloride

How do you recognize whether a formula—and through extension, a name—is because that a molecular compound or for an ionic compound? molecular compounds type between nonmetals and nonmetals, while ionic compounds form between metals and also nonmetals. The periodic table (Figure 3.2 "A straightforward Periodic Table") can be provided to determine which facets are metals and also nonmetals.

There also exists a team of ions that contain an ext than one atom. These are dubbed polyatomic ionsAn ion that contains more than one atom.. Table 3.7 "Common Polyatomic Ions" list the formulas, charges, and also names of some typical polyatomic ions. Only among them, the ammonium ion, is a cation; the remainder are anions. Many of them also contain oxygen atoms, so sometimes they are described as oxyanions. Few of them, such as nitrate and also nitrite, and also sulfate and sulfite, have very similar formulas and also names, so care must be taken to get the formulas and also names correct. Keep in mind that the -ite polyatomic ion has actually one less oxygen atom in its formula than the -ate ion but with the same ionic charge.

Table 3.7 usual Polyatomic Ions

surname Formula and also 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 specify name of ionic compounds that contain polyatomic ions follows the exact same rules together the specify name for various other ionic compounds: simply integrate the name of the cation and also the surname of the anion. Execute 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 surname of the ion itself includes a number prefix, such as dichromate or triiodide.

Writing the recipe of ionic compounds has actually one important difference. If much more than one polyatomic ion is necessary to balance the all at once charge in the formula, enclose the formula the the polyatomic ion in parentheses and also write the proper numerical subscript come the right and also outside the parentheses. Thus, the formula in between calcium ions, Ca2+, and also nitrate ions, NO3−, is correctly written Ca(NO3)2, not CaNO32 or CaN2O6. Usage parentheses where required. The name of this ionic compound is merely calcium nitrate.

Example 9

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

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


because the ammonium ion has actually a 1+ charge and the sulfide ion has a 2− charge, we need two ammonium ions to balance the fee on a solitary sulfide ion. Enclosing the formula for the ammonium ion in parentheses, we have actually (NH4)2S. The compound’s name is ammonium sulfide. Because the ions have the very same magnitude of charge, we require only one of each come balance the charges. The formula is AlPO4, and the name of the link is aluminum phosphate. Neither charge is an exact multiple of the other, so we need to go to the least common multiple of 6. To obtain 6+, we need three iron(II) ions, and also to obtain 6−, we require two phosphate ions. The proper formula is Fe3(PO4)2, and also the compound’s surname is iron(II) phosphate.

Test Yourself

Write the proper formula and give the appropriate name for each ionic link 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: sodium in her Food

The facet sodium, at the very least in that ionic kind as Na+, is a crucial nutrient for human beings to live. In fact, the human being body is approximately 0.15% sodium, v the average person having actually one-twentieth come one-tenth the a kilogram in their body at any kind of given time, largely in fluids external cells and in other bodily fluids.

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

Table 3.8 some 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, shade 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 plenty of sodium link in prepared and processed foods items has alarmed some physicians and also nutritionists. Lock argue that the average person consumes too lot sodium from his or she diet. The average person needs only around 500 mg of sodium every day; most human being consume more than this—up to 10 times as much. Part studies have actually implicated boosted sodium intake with high blood pressure; newer studies indicate that the attach is questionable. However, there has actually been a push to minimize the quantity of sodium most civilization ingest every day: avoid processed and manufactured foods, review labels ~ above packaged foodstuffs (which incorporate an indication of the sodium content), nothing oversalt foods, and also use other herbs and spices as well as salt in cooking.


Food labels incorporate the amount of salt per serving. This particular label shows that there are 75 mg of salt in one serving of this particular food item.

Key Takeaways

Ions form when atoms shed or gain electrons. Ionic compounds have actually positive ion and an adverse ions. Ionic formulas balance the total positive and an unfavorable charges. Ionic compounds have actually a basic system the naming. Teams of atoms can have an overall charge and make ionic compounds.


Explain just how cations form.

Explain how anions form.

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

K O Co

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

Ca i Fe

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

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Ag Au Br

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