As v ionic compounds, the system that chemists have actually devised because that naming covalent compounds permits us to compose the molecule formula native the name and also vice versa. In this and also the adhering to section, we describe the rules because that naming an easy covalent compounds. We begin with not natural compounds and also then rotate to an easy organic compounds the contain only carbon and hydrogen.

You are watching: Why are prefixes used in naming covalent compounds

Binary not natural Compounds

Binary covalent compounds—that is, covalent compounds the contain just two elements—are called using a procedure similar to that provided to name straightforward ionic compounds, but prefixes are added as essential to indicate the variety of atoms of every kind. The procedure, diagrammed in number 2.13 "Naming a Covalent not natural Compound", provides the following steps:

Figure 2.13 naming a Covalent inorganic Compound


Place the facets in their suitable order.

The element farthest come the left in the periodic table is usually named first. If both aspects are in the very same group, the facet closer come the bottom the the shaft is named first. The 2nd element is named as if it to be a monatomic anion in one ionic compound (even despite it is not), v the suffix -ide attached come the source of the element name.

Identify the variety of each form of atom present.

In part names, the last a or o the the prefix is to reduce to avoid awkward pronunciation. Therefore OsO4 is osmium tetroxide fairly than osmium tetraoxide.

Write the surname of the compound.

certain compounds space always dubbed by the usual names the were assigned long earlier when names rather than formulas to be used. Because that example, H2O is water (not dihydrogen oxide); NH3 is ammonia; PH3 is phosphine; SiH4 is silane; and B2H6, a dimer of BH3, is diborane. For plenty of compounds, the organized name and the typical name are both used frequently, so you should be familiar with them. Because that example, the organized name because that NO is nitrogen monoxide, but it is much more commonly dubbed nitric oxide. Similarly, N2O is usually called nitrous oxide rather than dinitrogen monoxide. Notification that the suffix -ic and also -ous are the exact same ones provided for ionic compounds.

Note the Pattern

Start v the element at the much left in the regular table and also work come the right. If 2 or much more elements space in the exact same group, begin with the bottom element and work up.

Example 8

Write the name of each binary covalent compound.

SF6 N2O4 ClO2

Given: molecular formula

Asked for: name that compound


A list the elements in order follow to your positions in the periodic table. Identify the variety of each form of atom in the chemistry formula and then usage Table 2.6 "Prefixes for Indicating the variety of Atoms in chemistry Names" to recognize the prefixes needed.

B If the compound includes oxygen, follow step 3a. If not, decide whether to usage the common name or the systematic name.


A although oxygen lies come the left that chlorine in the routine table, the is not named very first because ClO2 is an oxide of an aspect other than fluorine (step 3a). Consequently, chlorine is named first, yet a prefix is no necessary due to the fact that each molecule has actually only one atom of chlorine. B since there are two oxygen atoms, the compound is a dioxide. Hence the link is chlorine dioxide. It is widely used as a substitute for chlorine in municipal water treatment plants because, unequal chlorine, it does no react v organic compound in water to develop potentially toxic chlorinated compounds.


Write the surname of each binary covalent compound.

IF7 N2O5 OF2


iodine heptafluoride dinitrogen pentoxide oxygen difluoride

Example 9

Write the formula because that each binary covalent compound.

sulfur trioxide diiodine pentoxide

Given: name the compound

Asked for: formula


List the aspects in the exact same order as in the formula, usage Table 2.6 "Prefixes for Indicating the variety of Atoms in chemistry Names" to recognize the number of each form of atom present, and then show this quantity as a subscript to the best of that element when writing the formula.


Sulfur has actually no prefix, which method that each molecule has only one sulfur atom. The prefix tri- indicates that there space three oxygen atoms. The formula is as such SO3. Sulfur trioxide is created industrially in huge amounts together an intermediate in the synthetic of sulfuric acid. The prefix di- speak you the each molecule has two iodine atoms, and the prefix penta- suggests that over there are 5 oxygen atoms. The formula is for this reason I2O5, a compound provided to remove carbon monoxide from wait in respirators.


Write the formula because that each binary covalent compound.

silicon tetrachloride disulfur decafluoride


SiCl4 S2F10

The structures of some of the compounds in example 8 and also Example 9 are displayed in number 2.14 "The frameworks of some Covalent not natural Compounds and also the areas of the “Central Atoms” in the periodic Table", along with the location of the “central atom” that each compound in the regular table. It might seem that the compositions and structures of together compounds are completely random, yet this is not true. After ~ you have mastered the material in thing 7 "The periodic Table and also Periodic Trends" and also Chapter 8 "Ionic versus Covalent Bonding", you will have the ability to predict the compositions and structures of link of this kind with a high level of accuracy.

Figure 2.14 The frameworks of some Covalent inorganic Compounds and the locations of the “Central Atoms” in the regular Table


The compositions and structures the covalent inorganic compounds room not random. Together you will find out in chapter 7 "The periodic Table and also Periodic Trends" and Chapter 8 "Ionic versus Covalent Bonding", they can be predicted indigenous the locations of the component atom in the routine table.


Approximately one-third that the compounds created industrially room organic compounds. All living organisms space composed of essential compounds, together is many of the food friend consume, the drugs you take, the fibers in the clothing you wear, and the plastics in the products you use. Section 2.1 "Chemical Compounds" introduced two organic compounds: methane (CH4) and also methanol (CH3OH). These and also other necessary compounds appear frequently in discussions and also examples transparent this text.

The detection of essential compounds is useful in countless fields. In one recently developed application, scientists have devised a new method called “material degradomics” to do it feasible to screen the deterioration of old books and also historical documents. As paper ages, that produces a acquainted “old publication smell” indigenous the release of necessary compounds in gaseous form. The composition of the gas relies on the original form of record used, a book’s binding, and the used media. By examining these necessary gases and isolating the individual components, preservationists are far better able to identify the problem of an item and those books and also documents many in need of instant protection.

The simplest course of essential compounds is the hydrocarbonsThe simplest course of necessary molecules, consist of of just carbon and hydrogen., which consist totally of carbon and also hydrogen. Petroleum and also natural gas are complex, naturally emerging mixtures of countless different hydrocarbons the furnish raw materials for the chemistry industry. The four significant classes of hydrocarbons space the alkanesA saturated hydrocarbon with only carbon–hydrogen and also carbon–carbon solitary bonds., i beg your pardon contain just carbon–hydrogen and also carbon–carbon single bonds; the alkenesAn unsaturated hydrocarbon through at least one carbon–carbon double bond., i m sorry contain at the very least one carbon–carbon dual bond; the alkynesAn unsaturated hydrocarbon v at least one carbon–carbon triple bond., i beg your pardon contain at the very least one carbon–carbon triple bond; and the fragrant hydrocarbonsAn unsaturated hydrocarbon consists of a ring of six carbon atoms v alternating solitary and dual bonds., which usually contain rings of six carbon atom that have the right to be attracted with alternating solitary and double bonds. Alkanes are additionally called saturated hydrocarbons, vice versa, hydrocarbons the contain multiple bonds (alkenes, alkynes, and also aromatics) are unsaturated.


The most basic alkane is methane (CH4), a colorless, odorless gas that is the major component of organic gas. In bigger alkanes who carbon atoms space joined in an unbranched chain (straight-chain alkanes), every carbon atom is bonded to at many two various other carbon atoms. The frameworks of two straightforward alkanes are displayed in figure 2.15 "Straight-Chain Alkanes with Two and Three Carbon Atoms", and also the names and condensed structural formulas because that the an initial 10 straight-chain alkanes space in Table 2.7 "The first 10 Straight-Chain Alkanes". The name of all alkanes finish in -ane, and also their boiling points rise as the variety of carbon atoms increases.

Figure 2.15 Straight-Chain Alkanes through Two and Three Carbon Atoms


Table 2.7 The very first 10 Straight-Chain Alkanes

Name number of Carbon atoms Molecular Formula Condensed structure Formula Boiling suggest (°C) supplies
methane 1 CH4 CH4 −162 natural gas constituent
ethane 2 C2H6 CH3CH3 −89 natural gas constituent
propane 3 C3H8 CH3CH2CH3 −42 bottled gas
butane 4 C4H10 CH3CH2CH2CH3 or CH3(CH2)2CH3 0 lighters, bottled gas
pentane 5 C5H12 CH3(CH2)3CH3 36 solvent, gasoline
hexane 6 C6H14 CH3(CH2)4CH3 69 solvent, gasoline
heptane 7 C7H16 CH3(CH2)5CH3 98 solvent, gasoline
octane 8 C8H18 CH3(CH2)6CH3 126 gasoline
nonane 9 C9H20 CH3(CH2)7CH3 151 gasoline
decane 10 C10H22 CH3(CH2)8CH3 174 kerosene

Alkanes with four or an ext carbon atoms deserve to have an ext than one arrangement of atoms. The carbon atoms can type a solitary unbranched chain, or the major chain that carbon atoms can have one or more shorter chains that form branches. Because that example, butane (C4H10) has two feasible structures. Normal butane (usually called n-butane) is CH3CH2CH2CH3, in which the carbon atoms kind a single unbranched chain. In contrast, the condensed structure formula because that isobutane is (CH3)2CHCH3, in which the main chain of 3 carbon atoms has actually a one-carbon chain branching in ~ the main carbon. Three-dimensional depictions of both structures space as follows:


The methodical names for branched hydrocarbons use the lowest possible number to indicate the position of the branch follow me the longest directly carbon chain in the structure. Hence the organized name for isobutane is 2-methylpropane, which indicates that a methyl team (a branch consist of of –CH3) is attached to the second carbon of a propane molecule. Similarly, friend will learn in section 2.6 "Industrially crucial Chemicals" that one of the significant components of petrol is generally called isooctane; its framework is as follows:


As you can see, the compound has actually a chain of 5 carbon atoms, so the is a derivative the pentane. There room two methyl team branches at one carbon atom and one methyl group at another. Making use of the lowest feasible numbers for the branches offers 2,2,4-trimethylpentane for the systematic name the this compound.


The simplest alkenes are ethylene, C2H4 or CH2=CH2, and propylene, C3H6 or CH3CH=CH2 (part (a) in figure 2.16 "Some basic (a) Alkenes, (b) Alkynes, and (c) Cyclic Hydrocarbons"). The surname of alkenes that have much more than three carbon atoms use the exact same stems together the names of the alkanes (Table 2.7 "The very first 10 Straight-Chain Alkanes") yet end in -ene instead of -ane.

Once again, more than one structure is possible for alkenes with four or more carbon atoms. Because that example, an alkene with 4 carbon atoms has three possible structures. One is CH2=CHCH2CH3 (1-butene), which has actually the dual bond in between the an initial and 2nd carbon atoms in the chain. The various other two structures have the double bond between the 2nd and third carbon atoms and also are develops of CH3CH=CHCH3 (2-butene). All four carbon atom in 2-butene lie in the same plane, so there space two feasible structures (part (a) in number 2.16 "Some straightforward (a) Alkenes, (b) Alkynes, and (c) Cyclic Hydrocarbons"). If the 2 methyl groups are on the same side that the twin bond, the link is cis-2-butene (from the Latin cis, definition “on the same side”). If the two methyl teams are ~ above opposite political parties of the dual bond, the compound is trans-2-butene (from the Latin trans, definition “across”). These space distinctly different molecules: cis-2-butene melts in ~ −138.9°C, conversely, trans-2-butene melts at −105.5°C.

Figure 2.16 Some an easy (a) Alkenes, (b) Alkynes, and (c) Cyclic Hydrocarbons


The positions of the carbon atom in the chain are indicated by C1 or C2.

Just as a number suggests the positions of branches in an alkane, the number in the name of one alkene mentions the position of the first carbon atom that the twin bond. The name is based on the lowest possible number starting from either end that the carbon chain, so CH3CH2CH=CH2 is called 1-butene, not 3-butene. Keep in mind that CH2=CHCH2CH3 and also CH3CH2CH=CH2 are different ways of creating the same molecule (1-butene) in two various orientations.


The surname of a link does not rely on its orientation. As illustrated for 1-butene, both condensed structure formulas and also molecular models show different orientations the the very same molecule. Don’t let orientation stupid you; you must be able to recognize the very same structure no matter what its orientation.

Note the Pattern

The positions of teams or multiple bonds are always indicated by the lowest number possible.


The simplest alkyne is acetylene, C2H2 or HC≡CH (part (b) in number 2.16 "Some basic (a) Alkenes, (b) Alkynes, and also (c) Cyclic Hydrocarbons"). Because a mixture the acetylene and also oxygen burns with a flame the is hot enough (>3000°C) to reduced metals such as hardened steel, acetylene is widely offered in cutting and welding torches. The surname of various other alkynes are similar to those that the equivalent alkanes however end in -yne. For example, HC≡CCH3 is propyne, and CH3C≡CCH3 is 2-butyne since the many bond starts on the 2nd carbon atom.

Note the Pattern

The variety of bonds between carbon atoms in a hydrocarbon is shown in the suffix:

alkane: only carbon–carbon solitary bonds alkene: at the very least one carbon–carbon double bond alkyne: at least one carbon–carbon triple link

Cyclic Hydrocarbons

In a cyclic hydrocarbonA hydrocarbon in i m sorry the ends of the carbon chain are associated to kind a ring of covalently external inspection carbon atoms., the end of a hydrocarbon chain are connected to form a ring the covalently bonded carbon atoms. Cyclic hydrocarbons are named by attaching the prefix cyclo- come the surname of the alkane, the alkene, or the alkyne. The simplest cyclic alkanes space cyclopropane (C3H6) a flammable gas the is additionally a an effective anesthetic, and also cyclobutane (C4H8) (part (c) in figure 2.16 "Some basic (a) Alkenes, (b) Alkynes, and also (c) Cyclic Hydrocarbons"). The most common means to draw the frameworks of cyclic alkanes is to sketch a polygon with the same variety of vertices as there are carbon atom in the ring; each vertex to represent a CH2 unit. The frameworks of the cycloalkanes that contain 3 to six carbon atom are shown schematically in figure 2.17 "The simple Cycloalkanes".

Figure 2.17 The simple Cycloalkanes


Aromatic Hydrocarbons

Alkanes, alkenes, alkynes, and also cyclic hydrocarbons space generally referred to as aliphatic hydrocarbonsAlkanes, alkenes, alkynes, and also cyclic hydrocarbons (hydrocarbons that are not aromatic).. The name comes from the Greek aleiphar, definition “oil,” due to the fact that the first examples to be extracted from animal fats. In contrast, the very first examples the aromatic hydrocarbons, also called arenes, were derived by the distillation and also degradation of very scented (thus aromatic) resins from tropical trees.

The simplest fragrant hydrocarbon is benzene (C6H6), which was an initial obtained from a coal distillate. The word aromatic now refers to benzene and also structurally similar compounds. As presented in part (a) in number 2.18 "Two aromatic Hydrocarbons: (a) Benzene and (b) Toluene", it is feasible to draw the structure of benzene in 2 different but equivalent ways, depending upon which carbon atom are associated by twin bonds or single bonds. Toluene is similar to benzene, other than that one hydrogen atom is replaced by a –CH3 group; it has the formula C7H8 (part (b) in number 2.18 "Two aromatic Hydrocarbons: (a) Benzene and (b) Toluene"). Together you will soon learn, the chemical behavior of fragrant compounds differs from the habits of aliphatic compounds. Benzene and also toluene are discovered in gasoline, and also benzene is the beginning material because that preparing building material as diverse as aspirin and nylon.

Figure 2.19 "Two Hydrocarbons v the molecular Formula C" illustrates two of the molecule structures possible for hydrocarbons that have six carbon atoms. Together you have the right to see, compounds with the very same molecular formula can have very different structures.

Example 10

Write the condensed structural formula because that each hydrocarbon.

n-heptane 2-pentene 2-butyne cyclooctene

Given: name of hydrocarbon

Asked for: condensed structure formula


A usage the prefix to determine the number of carbon atoms in the molecule and also whether it is cyclic. Native the suffix, recognize whether multiple bonds are present.

B identify the place of any type of multiple bonds native the number(s) in the name and also then create the condensed structural formula.


A The prefix hept- tells united state that this hydrocarbon has seven carbon atoms, and n- indicates that the carbon atoms type a straight chain. The suffix -ane tells that it is an alkane, with no carbon–carbon dual or triple bonds. B The condensed structure formula is CH3CH2CH2CH2CH2CH2CH3, which can likewise be created as CH3(CH2)5CH3.

A The prefix pent- tells united state that this hydrocarbon has five carbon atoms, and also the suffix -ene shows that it is an alkene, with a carbon–carbon dual bond. B The 2- tells us that the dual bond begins on the 2nd carbon of the five-carbon atom chain. The condensed structure formula the the link is therefore CH3CH=CHCH2CH3.

A The prefix but- tells us that the compound has a chain of 4 carbon atoms, and also the suffix -yne indicates that it has actually a carbon–carbon triple bond. B The 2- tells us that the triple bond begins on the 2nd carbon that the four-carbon atom chain. Therefore the condensed structure formula for the link is CH3C≡CCH3.

A The prefix cyclo- tells united state that this hydrocarbon has a ring structure, and oct- indicates that it has eight carbon atoms, which us can draw as

The suffix -ene tells us that the compound consists of a carbon–carbon dual bond, however where in the ring perform we place the twin bond? B because all eight carbon atoms space identical, it no matter. Us can attract the framework of cyclooctene as


Write the condensed structural formula for each hydrocarbon.

n-octane 2-hexene 1-heptyne cyclopentane




The basic name because that a group of atoms derived from an alkane is an alkyl group. The name of an alkyl team is acquired from the name of the alkane by adding the suffix -yl. Thus the –CH3 fragment is a methyl group, the –CH2CH3 fragment is an ethyl group, and also so forth, whereby the dash to represent a single bond come some other atom or group. Similarly, teams of atoms obtained from aromatic hydrocarbons space aryl groups, i m sorry sometimes have unexpected names. For example, the –C6H5 fragment is acquired from benzene, but it is dubbed a phenyl group. In general formulas and structures, alkyl and aryl teams are regularly abbreviated together RThe abbreviation provided for alkyl groups and aryl groups in general formulas and also structures..


Structures that alkyl and aryl groups. The methyl group is an example of an alkyl group, and the phenyl group is an example of an aryl group.


Replacing one or more hydrogen atom of a hydrocarbon through an –OH group provides an alcoholA class of essential compounds derived by replacing one or an ext of the hydrogen atom of a hydrocarbon v an −OH group., represented as ROH. The most basic alcohol (CH3OH) is dubbed either methanol (its systematic name) or methyl alcohol (its usual name) (see number 2.4 "Different methods of Representing the structure of a Molecule"). Methanol is the antifreeze in vehicle windshield washer fluids, and also it is additionally used together an efficient fuel because that racing cars, most notably in the Indianapolis 500. Ethanol (or ethyl alcohol, CH3CH2OH) is acquainted as the alcohol in fermented or distilled beverages, such as beer, wine, and also whiskey; the is additionally used as a petrol additive (Section 2.6 "Industrially vital Chemicals"). The simplest alcohol acquired from an aromatic hydrocarbon is C6H5OH, phenol (shortened native phenyl alcohol), a potent disinfectant supplied in part sore throat medications and mouthwashes.

Ethanol, i beg your pardon is easy to obtain from fermentation processes, has efficiently been used as an different fuel for several decades. Although it is a “green” fuel when acquired from plants, the is one imperfect substitute because that fossil fuels since it is less reliable than gasoline. Moreover, due to the fact that ethanol absorbs water from the atmosphere, it can corrode an engine’s seals. Thus other species of processes are being arisen that usage bacteria to develop more complicated alcohols, such as octanol, that are an ext energy efficient and also that have a lower propensity to absorb water. As scientists attempt to mitigate mankind’s dependence on fossil fuels, the advancement of this so-called biofuels is a particularly active area the research.

See more: What Size Ham For 10 Adults, How Much Ham Do You Need Per Person


Covalent not natural compounds are named by a procedure comparable to that offered for ionic compounds, using prefixes to suggest the number of atoms in the molecular formula. The simplest organic compounds space the hydrocarbons, i m sorry contain only carbon and hydrogen. Alkanes contain just carbon–hydrogen and carbon–carbon solitary bonds, alkenes contain at the very least one carbon–carbon dual bond, and also alkynes save on computer one or an ext carbon–carbon triple bonds. Hydrocarbons can also be cyclic, through the end of the chain associated to type a ring. Collectively, alkanes, alkenes, and alkynes are called aliphatic hydrocarbons. Aromatic hydrocarbons, or arenes, are one more important class of hydrocarbons the contain rings of carbon atoms concerned the structure of benzene (C6H6). A derivative of one alkane or an arene native which one hydrogen atom has been gotten rid of is dubbed an alkyl group or one aryl group, respectively. Alcohols are one more common class of necessary compound, i beg your pardon contain an –OH team covalently external inspection to either an alkyl group or one aryl group (often abbreviation R).

Key Takeaway

Covalent inorganic compounds are named using a procedure similar to that offered for ionic compounds, whereas hydrocarbons use a system based upon the number of bonds in between carbon atoms.

Benzene (C6H6) is an necessary compound, and KCl is an ionic compound. The amount of the masses the the atoms in each empirical formula is approximately the same. How would you mean the two to compare through regard to every of the following? What varieties are current in benzene vapor?