Breakdown of Topics I.Chemical formulas, Relation to Type of Substances, “Formula Unit” concept, and Visual connections (related to Tro, 3.3, 3.4) II.Ionic.

Breakdown of Topics

I. Chemical formulas, Relation to Type of Substances, “Formula Unit” concept, and Visual connections (related to Tro, 3.3, 3.4)

II. Ionic Compound FormulasA. Difference between ions and ionic compounds (formula

writing)

B. The “neutrality principle” concept

III. Naming of Compounds (not elements!)A. Ionic Compounds

B. Binary Molecular Compounds

C. Acids1

I. Chemical Formulas Revisited• Related to “nanoscopic pictures”

– Every substance is composed of “basic units”– If sample A has “more of” a substance than sample B,

it has more “basic units” of that substance:

Sample A of NO2 Sample B of NO2

• Every substance has a single chemical formula that represents its “basic unit”

• One “unit” of any substance can be called a “formula unit”! (Here, one molecule = 1 formula unit)2

Reminder

Monatomic Molecular Molecular Ionic

Each of these has a chemical

formula…

…these do not have a chemical

formula

Note: there are four kinds of substances…

…and their formulas “tell you” which is which!...

How many substances are in the box?

How many chemical formulas would be needed to describe the matter in the box? 3

Quick quiz:

Ans. 2 (e.g., CS2 & O3)

Fig. 3.4 Four types of substances—relationship to nanoscopic entities & chemical formulae

Look closely at the different formulas—can tell the difference between an element and a compound? A monatomic vs polyatomic element? 4

How do you recognize a monatomic element from a formula?

• single element symbol with no subscript– Fe, Co, He

Fe (s) He (g)

Chemical formula

State designation

One “unit” of the substance. The chemical formula represents one unit

of a substance.

Unit = atom

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How do you recognize a molecular element from a formula?

• A single element symbol with a subscript– S8, N2, P4, C60

C60 (s) H2 (g)

Chemical formula

C60 Image: courtesy of J. Lauher's Fullerene Structure Library

One “unit” of the substance. The chemical formula represents one unit

of a substance.

Unit = molecule

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How do you recognize a molecular compound from a formula?

• more than one element symbol ( compound)• first one is NOT that of a metallic element (exception later)

( molecular)– CH4, SO2, SO3, P4O10

CH4 (s) SO3 (g)

Chemical formula

One “unit” of the substance. The chemical formula represents one unit of a substance.

Unit = molecule

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How do you recognize an ionic compound from a formula?

• more than one element symbol ( compound)• first one IS that of a metal (exceptions later) ( ionic)

– NaCl, FeCl3, CuSO4, Na3PO4

NaCl (s) FeCl3 (s)

Chemical formula

The chemical formula still represents one unit of a substance, but it is not a separate grouping as

in molecular substances.

Basic units are “ions”…

…but THE “unit” is a specific grouping of ions (indicated by the formula)

…what do you call “it” (the “unit”)?

…a “formula unit”!8

Formula units (FU) are the “basic units” of ionic compounds

• A formula unit is an amount of a substance. You can have:− one FU of NaCl or− Two FU of NaCl or− 25,333 FU of NaCl or− 1.56 x 1021 FU of NaCl

• Just like you can have:− one molecule of CO2 or

− Two molecules of CO2 or

− 25,333 molecules of CO2 or

− 1.56 x 1021 molecules of CO2

Quick Quiz: Can you have:4.3 FU of NaCl?0.5 FU of CO2?

NO! A FU is a “unit” of a substance—you cannot have a “fraction” of one! You can only have a whole number of them.

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Formula Unit is just another term for “basic unit” of any substance

• Most chemists use the term “formula unit” only with ionic compounds (b/c you can use “atom” or “molecule” for the other kinds of substances)

• However, I often use the term with monatomic elements or molecular substances as well

− e.g., 15 FU of CO2 means 15 molecules of CO2

− e.g., 432 FU of Fe means 432 atoms of Fe

• “More” of a substance means more “formula units” of it!

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How many FUs of each substance are present?

7 6 8 5

7 12 4

___ FU of Fe ___ FU of He ___ FU of CH4 ___ FU of SO3

___ FU of N2 ___ FU of NaCl ___ FU of FeCl311

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II. Ion and Ionic Compound Formulas

• The chemical formula of any ion MUST show the charge as a superscript on the right:– Na+, Ru3+, Ca2+, O2-, NO2

-, PO43-

• The chemical formula of any ionic compound MUST show NO CHARGES AT ALL!– Na2O, Ru2O3, Ca(NO2)2, Na3PO4

NOTE: Your only clue that a compound formula represents an ionic compound is noticing the metal in front (exception later)

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Subscripts of ions tell you how many (of each) are in 1 FU

Formula

Na2O

Ru2O3

Ca(NO2)2

Na3PO4

1 FU contains exactly:

Two Na+ ions and one O2- ion

Two Ru3+ ions and three O2- ions

One Ca2+ ion and two NO2- ions

Three Na+ ions and one PO43- ion

NOTE: Parentheses are used ONLY if more than one of a polyatomic ion is present in one FU.

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What determines the number of each ion in a formula unit of an ionic compound?

• The charges on the cation and anion that make it up!

• The oppositely charged ions will come together in the ratio that makes each formula unit electrically neutral– “neutrality principle”

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Neutrality Principle

• A formula unit is always NEUTRAL overallThe grouping of cations and anions must be

neutral overall!• Total positive charge = total negative charge

Formula

Na2O: Na+ Na+ O2- +1 + (+1) + (-2) = 0

Na3PO4 Na+ Na+ Na+ PO43-

3(+1) + 1(-3) = 016

Test: Use Neutrality Principle to Determine the Charge on an Ion

Assume you know that O forms 2- ions (i.e. “O” = O2-) What is the charge on the Ru ions in Ru2O3?

ANS: +3

3 x 2- = -6 for the three O2- ions.

The two Ru ions must add up to +6

2 x ___ = +6+3

charge per ion 17

Ru?

Ru?

O2-

O2-

O2-

1 FU of compound; net charge

must be zero

Test: Use Neutrality Principle to Determine the Charge on an Ion

What is the charge on the Pb ions in PbO2?

ANS: +4

2 x 2- = -4 for the two O2- ions.

The one Pb ion must add up to +4

**If you said +2 then you are using a shortcut instead of thinking about the MEANING of the subscripts! They are NOT “charges”—they represent the number of ions in 1 FU**

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Pb? O2-

O2-

1 FU of compound; net charge

must be zero

Use the neutrality principle to determine the formula for an ionic compound

Ions

Fe3+ & Br-

Ti4+ & S2-

Ca2+ & PO43-

NH4+ & SO4

2-

Formula:

FeBr3

TiS2

Ca3(PO4)2

(NH4)2SO4

Why do you need this skill? To determine the chemical formula from the name!

“Cobalt(III) carbonate” is composed of cobalt(III) ions (Co3+) and carbonate ions (CO3

2-): Formula is: _________ 19Co2(CO3)3

III.A Naming Ionic Compounds

• Cation Name + Anion Name That’s it!!!

• Hard part: names of the ions!

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Na+

Li+

K+

Rb+

Cs+

Be2+

Mg2+

Ca2+

Sr2+

Ba2+

Al3+

Zn2+

Ag+

Ra2+

Cations that always have the same charge (can memorize)

2) One Polyatomic cation: NH4+, ammonium ion

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Fr+

1) Monatomic, Type I cations (in this class)

Cations with more than one possible charge (Type II) need a Roman Numeral

• Any metal cation other than those on previous slide!– Any transition metal ion other than Ag+ or Zn2+

– Any metal ion directly under the staircase other than Al3+

• Must use neutrality principle to figure out the charge (if not given to you)!

• Write the charge as a Roman numeral in parentheses 22

Type II Cation Examples

• Fe3+ is iron(III) ion; Fe2+ is iron(II)

• Pb4+ is lead(IV) ion; Pb2+ is lead(II)

• Cu+ is copper(I) ion; Cu2+ is copper(II)• Cr6+ is chromium(VI) ion; Cr3+ is chromium(III)

• But: Ag+ is just silver ion (Type I)

Zn2+ is just zinc ion (Type I)

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Anions—Preliminary Comment

• It will be much easier to learn anion names if you know these nonmetal elements’ symbols and names (next slide).

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Anions—Three Endings(-ide, -ate, and –ite)

• -ides1) Monatomic

Use Periodic Table:

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2) Two polyatomic ones to memorizeCN- (cyanide); OH- (hydroxide)

P3-

Phosphide

Anions (continued)

• -ates– Polyatomic, contain oxygen (“oxoanions”)– Learn the four “core ions” first (next slide)

• Then others from them…

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Some “–ate” ions to learn first…

NO3- nitrate

SO42- sulfate

PO43- phosphate

CO32- carbonate

…and second (analogous to nitrate):

ClO3- chlorate

BrO3- bromate

IO3- iodate

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Mnemonic-- “Poconoso”

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PO CO

NO SO

3 2 1 2

PO43- CO3

2- NO3- SO4

2-

4 3 3 4

charge (negative)

# oxygen atoms

“Hydrogen ___” ions come from adding H+ to an oxoanion

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What’s the name of HS- ion?

• Ans: hydrogen sulfide (not on sheet!)

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Anions (continued)

• -ites– One less oxygen than “ate” counterpart

– Sulfate → sulfite (SO42- → SO3

2-)

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“-ites” come from “-ates”!

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“Per-” and “Hypo” in sets of four

ClO4-perchlorate (from “hyper”)

ClO- hypochlorite (from “hypo”)

ClO3- chlorate

ClO2- chlorite

• Summary: Prefixes of “per” (4 O’s) and “hypo” (1 O) are added in cases where there are four “versions” instead of two. 34

A few additional anions don’t follow any obvious pattern (memorize)

• MnO4- permanganate (analogous to ClO4

-)

• C2H3O2- acetate

• CrO42- chromate

• Cr2O72- dichromate

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Examples!!!

• See handout (and board for detailed solutions to Q’s below):

• BaCO3

• Fe(NO3)2

• PbCl4

• AgClO

barium carbonate

iron(II) nitratelead(IV) chloride

silver hypochlorite

• iron(II) hydroxide _________________

• magnesium phosphite _____________

Fe(OH)2

Mg3(PO3)2

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IIIB. Naming Binary Molecular Compounds

• “binary”-two different kinds of atoms (2 different elements’ symbols in formula)

• “molecular”- basic units are molecules– Molecules are made of atoms– Atoms are neutral– What’s the ratio of atoms in a molecule?

• NO SINGLE “ANSWER” It varies! (no “neutrality” principle to “restrict” b/c atoms already neutral!)

• CO and CO2; NO, N2O, NO2,, N2O4, etc. all exist!– Later, we’ll explore models of bonding…

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Naming Binary Molecular Compounds (continued)

• Thus, prefixes are needed to let the reader know what that ratio (and exact composition of a FU) is!– Note: NO2 and N2O4 mean different things even

though ratio is the same!

• General “Recipe” for name:– 1st Element Name + 2nd element’s stem + -ide– Add prefixes as needed to the element or element

stem • NOTE: “Mono” is left off 1st Element Name

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Examples

• N2O: dinitrogen monoxide

• NO2: nitrogen dioxide

• NO: nitrogen monoxide

• N2O4: dinitrogen tetroxide

• P4O10: tetraphosphorus decoxide

• CF4: carbon tetrafluoride

• SCl6: sulfur hexachloride

• http://www.youtube.com/watch?v=NJn76CR70oU (start at 3:20)

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The Prefixes You Need to Know

• 1: mono (only used on second element)• 2: di• 3: tri• 4: tetra• 5: penta• 6: hexa• 7: hepta• 8: octa• 9: nona• 10: deca

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Comment

• Do not confuse the –ide ending with the “ides” of actual anions!!!!!

• There are NO IONS in binary molecular compounds, even though the “ide” may make it sound as such!– CCl4, carbon tetrachloride does NOT contain any

chloride ions.– I wish that the naming system were completely

different for molecular compounds (no “–ides”), but I don’t get to decide!

• http://www.youtube.com/watch?v=NJn76CR70oU (start at 3:20) 41

Examples

• Sulfur trioxide __________________

• B2F6 __________________________

• SrF2 __________________________

SO3

diboron hexafluoride

strontium fluoride (no “di” here!**)

** The last one is ionic, not molecular! Make sure to identify “ionic” vs. “molecular” before you begin to name a substance!!

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IIIC. Acids—A subset of molecular compounds

• Molecular compounds that yield ions when dissolved in water!? (more later)

• Always have H written first• Imagine making any acid by adding H+‘s to any

anion in order to make a neutral formula unit.• The ENDING of the anion determines the name

of the acid:– Ide → hydro ___ic acid– Ate → ____ic acid– Ite → ____ous acid

•http://www.youtube.com/watch?v=a5nC2evhUa0

•http://www.youtube.com/watch?v=LoSLKUN7FQ4

(start at 1:35)

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Examples

• Hydrosulfuric acid _________________

• Sulfuric acid ______________________

• Chloric acid _______________________

• Hypochlorous acid _________________

• H3PO3 __________________________

• HNO3 ___________________________

• HNO2 ___________________________

• HCN ____________________________

H2SH2SO4

HClO3

HClOphosphorous acid

nitric acid

nitrous acid

hydrocyanic acid44

From Practice Handout

*You don’t need to memorize oxalate

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For some web practice

• http://www.stolaf.edu/depts/chemistry/courses/toolkits/125/js/naming/

• http://web.mst.edu/~gbert/names/Aionic.HTML– NOTE: This site does NOT do Type II metals at all!

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