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Naming Chemical Compounds ppt

The system for naming an ionic compound is different from that for naming a covalent compound, so before a compound can be named, it must be classified as ionic or covalent.

Classifying a compound is not an easy task, but for the purposes of naming them, we employ a simple test:

If the answer is yes, use the system for naming ionic compounds.

If the answer is no, use the system for naming covalent compounds.

Is there a metal or a polyatomic ion present?

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Naming Ionic Compounds

Ionic compounds are named simply by naming the ions present.

There are, however, two complicating factors:

I. Some metals form more than one ion.

I. Metals that form more than one ion, such as iron, add a Roman numeral to the name to indicate the charge:

Fe²⁺ is called iron (II) and Fe³⁺is called iron (III)

Assume a Roman numeral is required for any metal except

1. metals in groups IA and IIA on the periodic table

2. aluminum, cadmium, zinc, and silver

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Naming Ionic Compounds (continued)

If a Roman numeral is required, the charge on the metal ion must be determined from the charge on the negative ion.

Helpful Rules to Remember

Formula	Reasoning	Name
FeCl₂	Cl has a 1- charge, and there are 2 of them for a total of 2-, so the Fe must be 2+	iron (II) chloride
Fe₂O₃	O has a 2- charge, and there are 3 of them for a total of 6-, so the Fe must have a total charge of 6+ split equally between the two iron atoms, so each must have a 3+ charge	iron (III) oxide
PbS₂	S has a 2- charge, and there are 2 of them for a total of 4-, so the Pb must be 4+	lead (IV) sulfide
Cu₃N	N has a 3- charge, so the Cu must have a total charge of 3+ split equally between the 3 copper atoms, so each must have a 1+ charge	copper (I) nitride

Examples

A metal ion is always positive.

The Roman numeral indicates the charge, not the subscript.

The positive and negative charges must cancel (total charge must = 0).

Nonmetals are always negative & can never form more than one monatomic ion.

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Naming Ionic Compounds (continued)

II. Polyatomic ions each have specific names which must be memorized so they can be recognized on sight.

(At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.)

Formula	Name
C₂H₃O₂^1-	acetate
CO₃^2-	carbonate
HCO₃^1-	bicarbonate
NH₄¹⁺	ammonium

A few of the more common polyatomic ions

Formula	Name
NO₃^1-	nitrate
OH^1-	hydroxide
PO₄^3-	phosphate
SO₄^2-	sulfate

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Naming Ionic Compounds: Examples

Na₂SO₄

sodium sulfate

Fe(NO₃)₂

iron (II) nitrate

AlCl₃

aluminum chloride

PbI₄

lead (IV) iodide

(NH₄)₃PO₄

ammonium phosphate

Mg₃N₂

magnesium nitride

C₂H₃O₂^1-	acetate
CO₃^2-	carbonate
HCO₃^1-	bicarbonate
NH₄¹⁺	ammonium
NO₃^1-	nitrate
OH^1-	hydroxide
PO₄^3-	phosphate
SO₄^2-	sulfate
* Groups I & II, Al, Zn, Cd, and Ag need no Roman numeral.

AgC₂H₃O₂

silver acetate

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Naming Covalent Compounds

Covalent compounds are named by adding prefixes to the element names.

The compounds named in this way are binary covalent compounds.

‘Binary’ means that only two atoms are present.

‘Covalent’ (in this context) means both elements are nonmetals.

A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.)

A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘ide’.

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Naming Covalent Compounds

Prefixes

Subscript	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-

Subscript	Prefix
6	hexa-
7	hepta-
8	octa-
9	nona-
10	deca-

Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

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Naming Binary Covalent Compounds: Examples

N₂S₄

dinitrogen tetrasulfide

NI₃

nitrogen triiodide

XeF₆

xenon hexafluoride

CCl₄

carbon tetrachloride

P₂O₅

diphosphorus pentoxide

SO₃

sulfur trioxide

1	mono
2	di
3	tri
4	tetra
5	penta
6	hexa
7	heptaa
8	octa
9	nona
10	deca
* Second element in ‘ide’ from
* Drop –a & -o before ‘oxide’

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Naming Compounds: Practice

SiF₄

silicon tetrafluoride

Na₂CO₃

sodium carbonate

N₂O

dinitrogen monoxide

K₂O

potassium oxide

Cu₃PO₄

copper (I) phosphate

CoI₃

cobalt (III) iodide

Analysis	If “Yes”
* Is the cation a metal? (If so, does it need a Roman numeral?	The compound is ionic: name each ion present (DO NOT USE PREFIXES)
* Is there a polyatomic ion present?
* Are both elements nonmetals?	The compound is covalent: use prefixes (NO CHARGES EXIST)

PI₃

phosphorus triiodide

two nonmetals  covalent  use prefixes

metal present  ionic  no prefixes

Na  group I  no Roman numeral

two nonmetals  covalent  use prefixes

metal present  ionic  no prefixes

K  group I  no Roman numeral

metal present  ionic  no prefixes

Cu  not group I, II, etc.  add Roman numeral (PO₄ is 3-, each Cu must be 1+)

metal present  ionic  no prefixes

Co  not group I, II, etc.  add Roman numeral (I is 1-, total is 3-, Co must be 3+)

two nonmetals  covalent  use prefixes

NH₄Cl

ammonium chloride

NH₄  polyatomic ion present  ionic  no prefixes

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Writing Chemical Formulas: �A Review

I. Ionic Compounds

II. Covalent Compounds

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Classifying Compounds

Classifying a compound using its name is not as difficult as using its formula.

The names of covalent compounds will be easily recognized by the presence of the prefixes (mono-, di-, tri-, etc.).

If no prefixes are present in the name, the compound is ionic. (Exception: some polyatomic ion names always contain prefixes (such as dichromate) but those will be memorized and recognized as ions.)

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Writing Formulas for Ionic Compounds

Formulas for ionic compounds are written by balancing the positive and negative charges on the ions present.

The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s).

Polyatomic ion names must still be recognized from memory (e.g. ammonium nitrate), but metals will have a Roman numeral associated with them if there is the possibility of more than one ion (e.g. copper (I) chloride or copper (II) chloride). The Roman numeral indicates the charge on the ion not the number of ions in the formula.

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Writing Formulas for Ionic Compounds (continued)

Helpful Rules to Remember

Name	Reasoning	Formula
ammonium sulfate	NH₄ has a 1+ charge & SO₄ has a 2- charge, so 2 ammonium ions are required for each sulfate.	(NH₄)₂SO₄
zinc chloride	Zn has a 2+ charge & Cl has a 1- charge, so 2 chloride ions are required for each zinc ion.	ZnCl₂
copper (II) phosphate	Cu has a 2+ charge & PO₄ has a 3- charge, so 3 copper (II) ions are required for every two phosphate ions.	Cu₃(PO₄)₂

Examples

A metal ion is always positive.

The Roman numeral indicates the charge, not the subscript.

The positive and negative charges must cancel (total charge must = 0).

If more than one polyatomic ion is needed, put it in parentheses, and place a subscript outside the parentheses.

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Writing Formulas for Covalent Compounds

The names of covalent compounds contain prefixes that indicate the number of atoms of each element present.

Remember:

The compounds named in this way are binary covalent compounds (they contain only two elements, both of which are nonmetals).
When in covalent compounds, atoms do not have charges. Subscripts are determined directly from the prefixes in the name.

If no prefix is present on the name of the first element, there is only one atom of that element in the formula (its subscript will be 1).

A prefix will always be present on the name of the second element. The second element will use the form of its name ending in ‘-ide’.

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Writing Formulas for Binary Covalent Compounds: Examples

nitrogen dioxide

NO₂

diphosphorus pentoxide

P₂O₅

xenon tetrafluoride

XeF₄

sulfur hexafluoride

SF₆

1	mono
2	di
3	tri
4	tetra
5	penta
6	hexa
7	heptaa
8	octa
9	nona
10	deca
* Second element in ‘ide’ from
* Drop –a & -o before ‘oxide’

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Writing Formulas: Practice

carbon tetrafluoride

CF₄

Na₃PO₄

sodium phosphate

Cu₂SO₄

copper (I) sulfate

Analysis	If “Yes”
	The compound is covalent: the prefixes give the subscripts.
* Are there prefixes present	The compound is covalent: the prefixes give the subscripts.
No prefixes are present	The compound is ionic: subscripts must be determined by balancing charges

prefixes  covalent  prefixes indicate subscripts

metal  ionic  balance charges  3 Na¹⁺ needed for 1 PO₄^3-

metal present  ionic  balance charges 2 Cu¹⁺ needed for 1 SO₄^2-

Al₂S₃

aluminum sulfide

metal present  ionic  balance charges 2 Al³⁺ needed for 3 S^2-

N₂O₅

dinitrogen pentoxide

prefixes  covalent  prefixes indicate subscripts

NH₄NO₃

ammonium nitrate

polyatomic ion present  ionic  balance charges 

1 NH₄¹⁺ needed for 1 NO₃^1-

PbO₂

lead (IV) oxide

metal present  ionic  balance charges 1 Pb⁴⁺ needed for 2 O^2-

Fe₂(CO₃)₃

iron (III) carbonate

metal present  ionic  balance charges 2 Fe³⁺ needed for 3 CO₃^2-