naming compounds

Aim: How to Name compounds with polyatomic ions.

Materials: Index Cards, markers

Background information: REVIEW: (These compounds to follow ARE NOT binary compounds. They contain three or more elements, as opposed to only two in a binary compound. Don’t use the Greek method. That naming technique is used only for binary compounds of two nonmetals. That means, if you see a formula like BaSO₄, the name is not barium monosulfur tetraoxide. Many unaware students over the years have made this error and suffered for it.)

Goals: students should be able to learn to recognize the presence of a polyatomic ion in a formula.

Activity:

students will make a set of flashcards with the name on one side and the ion and its charge on the other. Then, carry them everywhere and use them. The cations used will be a mix of fixed charges AND variable charges. You must know which are which.

Students will associate the charges with each polyatomic ion. For example, NO₃¯ is called nitrate and it has a minus one charge.

Notes: _{glencoe chemistry, zumdahl & zumdahl}

1. When more than one polyatomic ion is required, parenthesis are used to enclose the ion with the subscript going outside the parenthesis. For example, the very first formula used is Fe(NO₃)₂. This means that two NO₃¯ are involved in the compound. Without the parenthesis, the formula would be FeNO₃₂, a far cry from the correct formula.

2. How to say a formula. When you speak a formula involving parenthesis out loud, you use the word “taken” as in the formula for ammonium sulfide, which is (NH₄)₂S. Out loud, you say “N H four taken twice S.” OR with the formula for copper(II) chlorate, which is Cu(ClO₃)₂. You say ” Cu Cl O three taken twice.”

Example #1 – write the name for Fe(NO₃)₂

Step #1 – decide if the cation is one showing variable charge. If so, a Roman numeral will be needed. In this case, iron does show variable charge.

If a variable charge cation is involved, you must determine the Roman numeral involved. You do this by computing the total charge contributed by the polyatomic ion. In this case, NO₃¯ has a minus one charge and there are two of them, making a total of minus 2.

Therefore, the iron must be a positive two, in order to keep the total charge of the formula at zero.

Step #2 – determine the name of the polyatomic ion. Nitrate is the name of NO₃¯.

The correct name is iron(II) nitrate. The common name would be ferrous nitrate.

Example #2 – write the name for NaOH

Step #1 – the cation, Na⁺, does not show a variable charge, so no Roman numeral is needed. The name is sodium.

Step#2 – OH¯ is recognized as the hydroxide ion.

The name of this compound is sodium hydroxide.

There are three things you must memorize: the name (hydroxide), the symbol (OH) and the charge (minus one).

Example #3 – write the name for KMnO₄

Step #1 – the cation, K⁺, does not show a variable charge, so no Roman numeral is needed. The name is potassium.

Step#2 – MnO₄¯ is recognized as the permanganate ion.

The name of this compound is potassium permanganate.

Example #4 – write the name for Cu₂SO₄

Step #1 – decide if the cation is one showing variable charge. If so, a Roman numeral will be needed. In this case, copper does show variable charge.

If a variable charge cation is involved, you must determine the Roman numeral involved. You do this by computing the total charge contributed by the polyatomic ion. In this case, SO₄²¯ has a minus two charge and there is only one, making a total of minus 2.

Therefore, the copper must be a positive one. Why? Well, there must be a positive two to go with the negative two in order to make zero. Since the formula shows two copper atoms involved, each must be a plus one charge.

Step #2 – determine the name of the polyatomic ion. Sulfate is the name of SO₄²¯.

The correct name is copper(I) sulfate. The common name would be cuprous sulfate.

Example #5 – write the name for Ca(ClO₃)₂

The first part of the name comes from the first element’s name: calcium. You also determine that it is not a cation of variable charge.

The second part of the name comes from the name of the polyatomic ion: chlorate.

This compound is named calcium chlorate.

Example #6 – write the name for Fe(OH)₃

Iron is an element with two possible oxidation states. The iron is a +3 charge because (1) there are three hydroxides, (2) hydroxide is a minus one charge, (3) this gives a total charge of negative three and (40 there is only one iron, so it must be a +3.

Therefore the first part of the name is iron(III).

The second part of the name is hydroxide, the name of the polyatomic ion.

The name of this compound is iron(III) hydroxide (or ferric hydroxide when using the common method).

Home work:

The cations in this first set are all of fixed oxidation state, so no Roman numerals are needed.

Write the correct name for:

1) AlPO₄

2) KNO₂

3) NaHCO₃

4) CaCO₃

5) Mg(OH)₂

6) Na₂CrO₄

7) Ba(CN)₂

8) K₂SO₄

9) NaH₂PO₄

10) NH₄NO₃

These formulas involve the use of a polyatomic ion. The cations are all of variable oxidation state, so Roman numerals are needed.

Write the correct name for:

11) Sn(NO₃)₂

12) FePO₄

13) Cu₂SO₄

14) Ni(C₂H₃O₂)₂

15) HgCO₃

16) Pb(OH)₄

17) Cu₂Cr₂O₇

18) Cu(ClO₃)₂

19) FeSO₄

20) Hg₂(ClO₄)₂

These formulas mix the use of the two types of cations.

Write the correct name for:

21) KClO₃

22) SnSO₄

23) Al(MnO₄)₃

24) Pb(NO₃)₂

25) Mg₃(PO₄)₂

26) CuH₂PO₄

27) CaHPO₄

28) Fe(HCO₃)₃

29) Na₂CO₃

30) MnSO₄

Homework: handout completion of chemical formulas or (p224 #19-23) ion pairs

Aim: How to name binary molecular compounds, when 2 nonmetals are involved.

Notes:_{glencoe science assessment}

1. A binary compound is one made of two different elements. There can
be one of each element such as in CO or NO. There can also be several
of each element such as BF or OCl₂.

2. In this type of compound there are no cations!

3. You dont have to know the charges. Just use the element names and their prefixes. Be aware that
heavy use of Greek number prefixes are used in this lesson.Here are the
first ten:

		one	mono-			six	hexa-
		two	di-			seven	hepta-
		three	tri-			eight	octa-
		four	tetra-			nine	nona-
		five	penta-			ten	deca-

Example #1 – write the name for N₂O.

Example #2 – write the name for NO₂.

Step #1 – part of the first name is the unchanged name of the first
element in the formula. In the examples above, it would be nitrogen.

If the subscript of the first element is 2 or more, you add a prefix
to the name. In the first example above, you would write dinitrogen. If
the subscript is one as in the second example above, you DO NOT use a prefix. You simply write the name, in this example it would be nitrogen.

Step #2 – the anion is named in the usual manner of stem plus “ide.”
In addition, a prefix is added. In the first example, the prefix is
“mono-” since there is one oxygen. In the second example, use “di-”
because of two oxygens.

The correct names of the two examples are dinitrogen monoxide and nitrogen dioxide.

Note that “monoxide” is written rather than “monooxide.” It sounds better when spoken out loud.

Example #3 – write the name for IF₇.

Step #1 – the first element is iodine and there is only one. This part of the name will be “iodine”, NOT “monoiodine.”

Step #2 – the second element is fluorine, so “fluoride” is used. Since there are seven, the prefix “hepta” is used.

The name of this compound is iodine heptafluoride.

Example #4 – write the name for N₂O₅.

Step #1 – the first element is nitrogen and there are two. This part of the name will be “dinitrogen.”

Step #2 – the second element is oxygen, so “oxide” is used. Since there are five, the prefix “penta” is used.

The name of this compound is “dinitrogen pentaoxide.” Many write is
as “dinitrogen pentoxide.” The ChemTeam believes that both are
considered correct, but the second is to be prefered.

Example #5 – write the name for XeF₂.

The first part of the name comes from the first element’s name: xenon. Since there is only one atom present, no prefix is used.

The second part of the name comes from the root of the second symbol
plus ‘ide’ as well as the prefix “di-,”therefore di + fluor + ide =
difluoride.

This compound is named xenon difluoride.

Example #6 – write the name for N₂O₄.

The first part of the name comes from the first element’s name:
nitrogen. Since there are two atoms, the prefix “di-” is used giving
dinitrogen.

The second part of the name comes from the root of the second symbol
plus ‘ide’ as well as the prefix “tetra-,”therefore tetr + ox + ide =
tetroxide.

This compound is named dinitrogen tetroxide. Notice the dropping of the “a” in tetra.

Just a reminder: this system of naming does not really have an
offically accepted name, but is often called the Greek system (or
method). It involves use of Greek prefixes when naming binary compounds
of two nonmetals.

Sometimes you will see the Stock system applied to these types of
compounds. Here is what the IUPAC currently says about that practice:
“The Stock notation can be applied to both cations and anions, but
preferably should not be applied to compounds between nonmetals.”

Acitivity
Write the correct name for:

1) As₄O₁₀

2) BrO₃

3) BN

4) N₂O₃

5) NI₃

6) SF₆

7) XeF₄

8) PCl₃

9) CO

10) PCl₅

Write the correct name for:

11) P₂O₅

12) S₂Cl₂

13) ICl₂

14) SO₂

15) P₄O₁₀

16) UF₆

17) OF₂

18) ClO₂

19) SiO₂

20) BF₃

Write the correct name for:

21) N₂S₅

22) CO₂

23) SO₃

24) XeF₆

25) KrF₂

26) BrCl₅

27) SCl₄

28) PF₃

29) XeO₃

30) OsO₄

Tag: naming compounds

How to Name Binary Molecular Compounds

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