Naming Inorganic Non-Metallic Binary Covalent Compounds Chemistry Tutorial

Key Concepts

A binary compound is made up of two different elements.
This tutorial looks at binary compounds in which both elements are non-metals.

A binary covalent compound refers to two different elements which are joined together by covalent bonds in a molecule.

Inorganic compounds are, in general, compounds that do not contain carbon.⁽¹⁾
There are notable exceptions such carbon monoxide (CO) and carbon dioxide (CO₂) for example.

Inorganic non-metallic binary covalent compounds can be named based on the composition of the compound (referred to as compositional nomenclature⁽²⁾).

The name of an inorganic non-metallic binary covalent compound using compositional nomenclature tells us:
⚛ which two elements are present in a molecule of the compound

⚛ number of atoms of each element present in a molecule of the compound

Using compositional nomenclature, non-metallic elements in inorganic binary covalent compounds are named in the following order from the element named first to the element named last:⁽³⁾
carbon, phosphorus, nitrogen, hydrogen, sulfur, oxygen, iodine, bromine, chlorine, fluorine

Apart from hydrogen, this order is based on the non-metallic element's location in the periodic table as shown below: ⁽⁴⁾

(Start with carbon, C, then follow the arrows around to fluorine, F )

In the name of the inorganic non-metallic binary covalent compound, the element that is:

(a) named first retains its name (the name is not modified)

(b) named last has a modified name ending in "ide" as shown in the table below:

element's name	modified name of element
flourine	fluoride
chlorine	chloride
bromine	bromide
iodine	iodide
oxygen	oxide
sulfur	sulfide
hydrogen	hydride
nitrogen	nitride
phosphorus	phosphide
carbon	carbide

A multiplicative prefix⁽⁵⁾ precedes the name of the element, or modified name of the element, and is joined directly to the name (no spaces nor hyphens between the prefix and the name) in order to tell us how many atoms of this element are present in a molecule of the inorganic non-metallic covalent compound:

No. of atoms	1	2	3	4	5	6	7	8	9	10
Multiplicative prefix	mono	di	tri	tetra	penta	hexa	hepta	octa	nona	deca

Using compositional nomenclature the two parts of the name of the inorganic non-metallic binary covalent compound are separated by a space:

first part last part

prefixname prefixnamide

Exceptions to the IUPAC recommendations for naming inorganic non-metallic binary covalent compounds:

(i) The final vowel⁽⁶⁾ of the multiplicative prefix should NOT be elided (should NOT be removed).
The exception is that if 1 oxygen atom is present it is usually named as a monoxide NOT as a monooxide.
IUPAC allows this exception because the form "monoxide" has been in general useage for a very long time.
Note that both versions of the name, monoxide AND monooxide are acceptable IUPAC names.

(ii) The prefix mono is not used in the final name of the compound UNLESS the name could be ambiguous without it (could apply to more than one compound).⁽⁷⁾ Even when more than one compound can be formed using the same two elements in different ratios, then mono prefix is often dropped.
For example carbon monoxide is the name of the compound with the fomula CO and carbon dioxide is the name of the compound with the formula CO₂.
1 atom of carbon is present in both molecules so we don't need to write monocarbon.
The number of oxygen atoms does differ in the two compounds so we distinguish between the two using the di and tri multiplicative prefixes before the name oxide.
If in doubt it is better to retain the "mono" prefix, it won't be wrong, but it may not be the name that is in common useage by chemists.

(iii) Some compounds have names that are accepted by IUPAC even though they are not systematically named. Examples you might encounter during your chemistry course include:⁽⁸⁾

⚛ water for H₂O (not dihydrogen monoxide)

⚛ hydrogen peroxide or dihydrogen peroxide for H₂O₂ (not dihydrogen dioxide)

⚛ either hydrogen sulfide or dihydrogen sulfide is an acceptable IUPAC name for H₂S

⚛ ammonia for NH₃ (not nitrogen trihydride)

(iv) Compositional names are not the preferred naming system for some compounds. Examples you might encounter in your chemistry course include:

⚛ diazene for N₂H₂ (not dinitrogen dihydride)

⚛ hydrazine for N₂H₄ (not dinitrogen tetrahydride)

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Steps for Naming Inorganic Non-metallic Binary Covalent Compunds Given the Formula for the Compound

Follow the steps below to name an inorganic non-metallic binary covalent compound given the molecular formula of the compound:

Break the molecular formula (X_aY_b) up into two parts to represent the two different elements (X_a and Y_b) with a space between the two parts:

Molecular Formula: X_aY_b

first part last part

X_a Y_b

Use the periodic table to help you name each element (name X and name Y):

Molecular Formula: X_aY_b
first part		last part
X_a		Y_b
xname_a		yname_b

(Note: the names of each element will be in lower case letters, no uppercase or capital letters)

Determine which element (X or Y) should be named first:

(i) If the molecular formula follows IUPAC guidelines, then the first chemical symbol in the molecular formula will be named first.
(ii) If the molecular formula does not follow IUPAC guidelines, then you will need to follow the arrows in the diagram below to determine which element should be named first:

(Carbon would always be named first, fluorine would always be named last.)

Molecular Formula: X_aY_b
first part		last part
X_a		Y_b
xname_a		yname_b

Modify the name of the element which is named last by removing its ending and replacing it with "ide".

ide replaces theses name endings: ine, ygen, ogen, orus, ur, on

Molecular Formula: X_aY_b
first part		last part
X_a		Y_b
xname_a		yname_b
xname_a		ynamide_b

Use the subscript numbers to the right of the element's symbol in the molecular formula to determine how many atoms of each element are present in the molecule.

If there is no subscript number to the right of the element's symbol, then only 1 atom of this element is present.

Molecular Formula: X_aY_b
first part		last part
X_a		Y_b
a atoms of xname		b atoms of ynamide

Convert the "number of atoms" to a multiplicative prefix:

No. of atoms	1	2	3	4	5	6	7	8	9	10
Multiplicative prefix	mono	di	tri	tetra	penta	hexa	hepta	octa	nona	deca

and attach the prefix directly to the name (no spaces nor hyphens to be used):

Molecular Formula: X_aY_b
first part		last part
a atoms of xname		b atoms of ynamide
prefixxname		prefixynamide

Do a final check on the name:
⚛ monooxides are named as monoxides

⚛ Do you really need to use a "mono" prefix?
If 1 atom of an element is always present when combined with the other element you do NOT need to write "mono".

⚛ Is this the name that is not only acceptable but also the one commonly used?
water (H₂O), hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S), ammonia (NH₃)

Assemble the final name by writing the name of each part in the correct order and separated by a space:
prefixxname prefixynamide

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Worked Examples of Naming Binary Inorganic Non-metallic Covalent Compounds

Question 1: Name the binary inorganic compound that has the formula NO₂ using IUPAC compositional nomenclature rules.

Solution:

Break the molecular formula (NO₂) up into two parts with a space between the two parts:

Molecular Formula: NO₂

first part last part

N O₂

Use the periodic table to help you name each element (name N and name O):

Molecular Formula: NO₂
first part		last part
N		O₂
nitrogen		oxygen₂

Determine which element should be named first:

(i) If the molecular formula follows IUPAC guidelines, then the first symbol in the formula will be named first.
(ii) If the molecular formula does not follow IUPAC guidelines, then you will need to follow the arrows in the diagram below:

(nitrogen occurs before oxygen in the sequence so nitrogen is named first)

Molecular Formula: NO₂
first part		last part
N		O₂
nitrogen		oxygen₂

Modify the name of the element which is named last by removing its ending and replacing it with "ide".

ide replaces theses name endings: ine, ygen, ogen, orus, ur, on

Molecular Formula: NO₂
first part		last part
N		O₂
nitrogen		ox~~ygen~~₂
nitrogen		oxide₂

Use the subscript numbers to the right of the element's symbol in the molecular formula to determine how many atoms of each element are present in the molecule.

If there is no subscript number to the right of the element's symbol, then only 1 atom of this element is present.

Molecular Formula: NO₂
first part		last part
N		O₂
nitrogen		oxide₂
1 atom of nitrogen		2 atoms of oxide

Convert the "number of atoms" to a multiplicative prefix:

No. of atoms	1	2	3	4	5	6	7	8	9	10
Multiplicative prefix	mono	di	tri	tetra	penta	hexa	hepta	octa	nona	deca

and attach the prefix directly to the name (no spaces nor hyphens to be used):

Molecular Formula: NO₂
first part		last part
1 atom of nitrogen		2 atoms of oxide
mononitrogen		dioxide

(Note: the "i" is retained in the prefix "di" when it is added to "oxide")

Do a final check on the name:
⚛ monooxides are named as monoxides

⚛ Do you really need to use a "mono" prefix?
There will be no ambiguity in the name if you write nitrogen dioxide instead of mononitrogen dioxide.

⚛ Is this the name that is not only acceptable but also the one commonly used?
water (H₂O), hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S), ammonia (NH₃)

Assemble the final name by writing the name of each part in the correct order and separated by a space:
nitrogen dioxide

Question 2: Name the binary inorganic compound that has the formula N₂O using IUPAC compositional nomenclature rules.

Solution:

Break the molecular formula (N₂O) up into two parts with a space between the two parts:

Molecular Formula: N₂O

first part last part

N₂ O

Use the periodic table to help you name each element (name N and name O):

Molecular Formula: N₂O
first part		last part
N₂		O
nitrogen₂		oxygen

Determine which element should be named first:

(i) If the molecular formula follows IUPAC guidelines, then the first symbol in the formula will be named first.
(ii) If the molecular formula does not follow IUPAC guidelines, then you will need to follow the arrows in the diagram below:

(nitrogen occurs before oxygen in the sequence so it is named first)

Molecular Formula: N₂O
first part		last part
N₂		O
nitrogen₂		oxygen

Modify the name of the element which is named last by removing its ending and replacing it with "ide".

ide replaces theses name endings: ine, ygen, ogen, orus, ur, on

Molecular Formula: N₂O
first part		last part
N₂		O
nitrogen₂		ox~~ygen~~
nitrogen₂		oxide

Use the subscript numbers to the right of the element's symbol in the molecular formula to determine how many atoms of each element are present in the molecule.

If there is no subscript number to the right of the element's symbol, then only 1 atom of this element is present.

Molecular Formula: N₂O
first part		last part
nitrogen₂		oxide
2 atoms of nitrogen		1 atom of oxide

Convert the "number of atoms" to a multiplicative prefix:

No. of atoms	1	2	3	4	5	6	7	8	9	10
Multiplicative prefix	mono	di	tri	tetra	penta	hexa	hepta	octa	nona	deca

and attach the prefix directly to the name (no spaces nor hyphens to be used):

Molecular Formula: N₂O
first part		last part
2 atoms of nitrogen		1 atom of oxide
dinitrogen		monooxide

Do a final check on the name:
⚛ monooxides are named as monoxides:
dinitrogen monooxide will be named as dinitrogen monoxide

⚛ Do you really need to use a "mono" prefix?
There will be no ambiguity in the name if you write dinitrogen oxide instead of dintrogen monoxide.

⚛ Is this the name that is not only acceptable but also the one commonly used?
Yes it is. The name nitrous oxide for the N₂O molecule is no longer an acceptable IUPAC name.

Assemble the final name by writing the name of each part in the correct order and separated by a space:
dinitrogen oxide

Question 3: Name the binary inorganic compound that has the formula N₂O₅ using IUPAC compositional nomenclature rules.

Solution:

Break the molecular formula (N₂O₅) up into two parts with a space between the two parts:

Molecular Formula: N₂O₅

first part last part

N₂ O₅

Use the periodic table to help you name each element (name N and name O):

Molecular Formula: N₂O₅
first part		last part
N₂		O₅
nitrogen₂		oxygen₅

Determine which element should be named first:

(i) If the molecular formula follows IUPAC guidelines, then the first symbol in the formula will be named first.
(ii) If the molecular formula does not follow IUPAC guidelines, then you will need to follow the arrows in the diagram below:

(nitrogen occurs before oxygen in the diagram so nitrogen is named first)

Molecular Formula: N₂O₅
first part		last part
N₂		O₅
nitrogen₂		oxygen₅

Modify the name of the element which is named last by removing its ending and replacing it with "ide".

ide replaces theses name endings: ine, ygen, ogen, orus, ur, on

Molecular Formula: N₂O₅
first part		last part
N₂		O₅
nitrogen₂		ox~~ygen~~₅
nitrogen₂		oxide₅

Use the subscript numbers to the right of the element's symbol in the molecular formula to determine how many atoms of each element are present in the molecule.

If there is no subscript number to the right of the element's symbol, then only 1 atom of this element is present.

Molecular Formula: N₂O₅
first part		last part
nitrogen₂		oxide₅
2 atoms of nitrogen		5 atoms of oxide

Convert the "number of atoms" to a multiplicative prefix:

No. of atoms	1	2	3	4	5	6	7	8	9	10
Multiplicative prefix	mono	di	tri	tetra	penta	hexa	hepta	octa	nona	deca

and attach the prefix directly to the name (no spaces nor hyphens to be used):

Molecular Formula: N₂O₅
first part		last part
2 atoms of nitrogen		5 atoms of oxide
dinitrogen		pentaoxide

(Note: the "a" is retained in the prefix "penta" when it is added to "oxide")

Do a final check on the name:
⚛ monooxides are named as monoxides

⚛ Do you really need to use a "mono" prefix?
If 1 atom of an element is always present when combined with the other element you do NOT need to write "mono".

⚛ Is this the name that is not only acceptable but also the one commonly used?
water (H₂O), hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S), ammonia (NH₃)
Yes. There is no other commonly used, acceptable IUPAC compositional name.

Assemble the final name by writing the name of each part in the correct order and separated by a space:
dinitrogen pentaoxide

Question 4: Name the binary inorganic compound that has the formula OCl₂ using IUPAC compositional nomenclature rules.⁽⁹⁾

Solution:

Break the molecular formula (OCl₂) up into two parts with a space between the two parts:

Molecular Formula: OCl₂

first part last part

O Cl₂

Use the periodic table to help you name each element (name O and name Cl):

Molecular Formula: OCl₂
first part		last part
O		Cl₂
oxygen		chlorine₂

Determine which element should be named first:

(i) If the molecular formula follows IUPAC guidelines, then the first symbol in the formula will be named first.
(ii) If the molecular formula does not follow IUPAC guidelines, then you will need to follow the arrows in the diagram below:

(oxygen occurs before chlorine in the sequence so oxygen is named first)

Molecular Formula: OCl₂
first part		last part
O		Cl₂
oxygen		chlorine₂

Modify the name of the element which is named last by removing its ending and replacing it with "ide".

ide replaces theses name endings: ine, ygen, ogen, orus, ur, on

Molecular Formula: OCl₂
first part		last part
O		Cl₂
oxygen		chlor~~ine~~₂
oxygen		chloride₂

Use the subscript numbers to the right of the element's symbol in the molecular formula to determine how many atoms of each element are present in the molecule.

If there is no subscript number to the right of the element's symbol, then only 1 atom of this element is present.

Molecular Formula: OCl₂
first part		last part
O		Cl₂
oxygen		chloride₂
1 atom of oxygen		2 atoms of chloride

Convert the "number of atoms" to a multiplicative prefix:

No. of atoms	1	2	3	4	5	6	7	8	9	10
Multiplicative prefix	mono	di	tri	tetra	penta	hexa	hepta	octa	nona	deca

and attach the prefix directly to the name (no spaces nor hyphens to be used):

Molecular Formula: OCl₂
first part		last part
1 atom of oxygen		2 atoms of chloride
monooxygen		dichloride

Do a final check on the name:
⚛ monooxides are named as monoxides

⚛ Do you really need to use a "mono" prefix?
There will be no ambiguity in the name if you write oxygen dichloride instead of monooxygen dichloride.

⚛ Is this the name that is not only acceptable but also the one commonly used?
water (H₂O), hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S), ammonia (NH₃)
Yes it is. You may see the name dichlorine oxide used, as you may also see the molecular formula given as Cl₂O but neither this name nor this molecular formula are acceptable under the current IUPAC recommendations.⁽⁹⁾

Assemble the final name by writing the name of each part in the correct order and separated by a space:
oxygen dichloride

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Footnotes: reference "Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005" (Red Book)

(1) Compounds containing carbon are called organic compounds. You can find out more about the IUPAC conventions for naming organic compounds in the Introduction to Naming Organic Compounds Tutorial.
Inorganic chemistry and organic chemistry are two separate areas within chemistry because the chemistry of carbon is quite different to the chemistry of other elements.

(2) There are 3 primary IUPAC systems for naming an inorganic compound:
(a) Compositional nomenclature : requires no understanding of the structure of the connections within the compound and is the system of nomenclature we will use here in this introduction to naming inorganic non-metallic binary covalent compounds.
(Strictly speaking we are using a specific type of compositional nomenclature known as stoichiometric nomenclature because we will be indicating the number of atoms of each element using multiplicative prefixes).
(b) Substitutive nomenclature : requires an understanding of connections within the structure of the compound
(c) Additive nomenclature : requires an understanding of connections within the structure of the compound and this is the most generally applicable system for inorganic compounds

(3) In constructing a stoichiometric name for an inorganic binary non-metallic covalent compound, one element is designated as the electropositive constituent and the other element is designated as the electronegative constituent.
The electropositive constituent is, by convention, the element that occurs first in the sequence given in the diagram.
The order of the elements in the diagram has its basis in consideration of the electronegativity of each element, that is, electronegativity generally decreases going down each group from top to bottom, and increases across a period from left to right.
The same order is used to write molecular formula of binary inorganic molecules, and, to name these molecules.

(4) This eliminates the previous problems of using strict "electronegativity" of elements to order the names of the elements.
Note that compounds containing oxygen are longer named as oxides UNLESS oxygen appears last in the molecular formula based on the diagram. Previously, compounds containing chlorine and oxygen would have been named as oxides, now they are named as chlorides.

(5) More multiplicative prefixes are given in the table below:

No. atoms	Prefix	No. atoms	Prefix	No. atoms	Prefix
11	undeca	21	henicosa	60	hexaconta
12	dodeca	22	docosa	70	heptaconta
13	trideca	23	tricosa	80	octaconta
14	tetradeca	30	triaconta	90	nonaconta
15	pentadeca	31	hentriaconta	100	hecta
16	hexadeca	35	pentatriaconta	200	dicta
17	heptadeac	40	tetraconta	500	pentacta
18	octadeca	48	octatetraconta	1000	kilia
19	nonadeca	50	pentaconta	2000	dilia
20	icosa	52	dopentaconta

(6) There are 5 vowels in the english alphabet. These are: a, e, i, o, u

(7) Herein lies the reason why the "hydrogen names" for some ions are named without a space between "hydrogen" and the name of the rest of the ion.
Consider the compositional names "hydrogen sulfide" and "hydrogen sulfide(2-)".
Hydrogen sulfide could have the formula HS^- as well as the formula H₂S.
Hydrogen sulfide(2-) could also refer to the formula HS^- as well as H₂S.
H₂S is therefore named dihydrogen sulfide or more commonly hydrogen sulfide, while HS^- is named hydrogensulfide, monohydrogensulfide, or hydrogensulfide(1-) (hydrogen names) to avoid confusion.
The "hydrogen name" hydrogensulfide (all one word with no spaces) will ONLY apply to a hydrogen sulfide molecule (H₂S) that has lost a proton to become the hydrogensulfide ion, HS^-.

(8) Some names that have been in common useage for a long time are no longer acceptable IUPAC names. Some examples are:
(a) nitric oxide for NO is no longer acceptable. Acceptable names include nitrogen monoxide and nitrogen monooxide.
(b) nitrous oxide for N₂O is no longer acceptable. An acceptable IUPAC name is dinitrogen oxide.
(c) phosphine for PH₃ is no longer acceptable. The acceptable IUPAC name for this compound as a parent hydride is phosphane.

(9) In older textbooks you will see the molecular formula Cl₂O for this compound instead of OCl₂. This is because in previous nomenclature the elements were ordered strictly on the basis of increasing electronegativity in which oxygen is more electronegative that chlorine, so chlorine was named first and oxygen was named last as the oxide.
The most recent IUPAC recommendations use the relative positions in the periodic table as given in the diagram (with the arrows) to place the elements in order. So the IUPAC molecular formula for this compound will be OCl₂ and its name will be oxygen dichloride.

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