91833 Putting Ions in Their · PDF fileFlinn Scientific—Teaching Chemistry eLearning Video Series eLearning 2009 91833 011509 Publication No. 91833 Putting Ions in Their Hands Covalent,

Flinn Scientific—Teaching Chemistry� eLearning Video Series

eLearning 2009

91833011509

Publication No. 91833

Putting Ions in Their HandsCovalent, Ionic and Metallic Bonding

Introduction

The first time seeing formulas and names of ionic compounds can be confusing. However, upon further investigation, there are actually simplistic formulated steps to do so. Discover a systematic method of writing formulas for ionic compounds without the need to experimentally determine each formula using cation and anion cards.

Concepts

• Ionic compounds • Formula writing • Cations and anions

Background

The chemical formula of a compound indicates the kinds of atoms and the relative number of each atom that is combined together to form the compound. Subscripts are the numbers written after the chemical element symbols and are used to indicate the number of atoms of each element in the compound. Water, the most abundant chemical on Earth, has the chemical formula H2O and has a whole-number hydrogen:oxygen atom ratio of 2 to 1.

Some compounds such as sodium chloride, which is common table salt, are composed of ions. Ions are atoms or groups of atoms that have a net positive or negative charge. Cations are atoms or groups of atoms with a net positive charge, such as Cu2+ or NH4

+, while anions are atoms or groups of atoms with a net negative charge, such as O2– or NO3

–. Atoms of metallic elements tend to form cations while atoms of nonmetallic elements tend to form anions. Ions join together because of an oppositely-charged or electrostatic attraction between a positive cation and a negative anion resulting in an ionic bond. Compounds held together by ionic bonds are ionic compounds.

Ionic compounds are generally composed of an extended network of positively-charged metal ions and negatively-charged nonmetal ions. Although composed of ions, ionic compounds are electrically neutral, i.e., the total positive charge is equal to the total negative charge. The chemical formula indicates the smallest whole-number ratio of each element in the network of ions and is called a formula unit. For example, magnesium chloride has the chemical formula MgCl2. The magnesium cation (Mg2+) and chloride anions (Cl–) combine in a 1:2 ratio to form MgCl2. The overall charge on the resulting ionic compound is zero. Thus the final compound is composed of two Cl– ions for each Mg2+ ion.

Some ions consist of a group of covalently bonded atoms that tend to stay together as if they were a single ion. Such ions are called polyatomic ions. An example is the nitrate ion, NO3

–. This polyatomic anion contains one nitrogen atom covalently bonded to three oxygen atoms and has an overall charge of –1. Calcium cations, Ca2+, in the presence of nitrate anions, NO3

–, will com-bine in a ratio of two nitrate ions for every calcium ion in order to balance the positive and negative charges and achieve electrical neutrality. Thus, the formula for calcium nitrate is written as Ca(NO3)2, showing that for every calcium ion there are two nitrate ions. Notice that the polyatomic ion is put in parentheses as a unit with the subscript on the outside of the parentheses.

Writing formulas for ionic compounds may be simply determined by following the steps below:

1. The cation is always written first; the anion is written second.

2. The overall charge for an ionic compound is always zero. The charges of the individual ions are never included in the com-pound’s formula.

3. Subscripts are used to indicate the number of atoms of each element in the compound.

4. Parentheses are used around polyatomic ions to show that the subscript pertains to the polyatomic ion as a whole.

5. Assumed subscripts of one are omitted when writing chemical formulas.

– 2 –

© 2009 Flinn Scientific, Inc. All Rights Reserved. 91833

Materials

Data Table Scissors

Envelope Sheet of anions

Ion Formula Chart Sheet of cations

Safety Precautions

This classroom activity is considered nonhazardous. Follow all classroom safety guidelines.

Preparation

Copy the appropriate number of Data Tables, Ion Formula Charts, and Model of Cation–Anion Sheets for each lab group.

Procedure

1. Working in teams or individually, cut all of the positive ion cards from the cation sheet and all of the negative ion cards from the anion sheet. Separate the cations from the anions.

2. Observe carefully the ion cards that have been cut. What do you notice about the height of the cards? What is the relation-ship between the height and the ion charge?

3. Locate the data table and the Ion Formula Chart.

4. From the cation and anion cards, locate ion cards for the first two combining ions listed in the first column of the data table. The first two, for example, are the aluminum cation and chloride anion. Copy the ionic formula for each ion into the first column of the data table. Use the Ion Formula Chart to look up the ion formulas.

5. Put the cards for the two combining substances together on a flat surface adding additional cards of the same ion until the heights of the cation and anion column are equal. For example, every aluminum cation needs three chloride anions (see Figure 1).

Figure 1. Aluminum chloride

6. Count the number of each ion necessary for the heights to be equal (i.e., for the compound to form). For example, one aluminum cation combines with three chloride anions. Record the number of each ion used in Columns 2 and 3 of the data table. Notice that the numbers recorded in Columns 2 and 3 are the subscripts in the chemical formula of the compound.

7. Determine the total positive charge of the cation card(s) and the total negative charge of the anion card(s) used in forming the compound. These two values will be equal yet opposite in value. For example, the total positive charge is +3 (from one aluminum with a +3 charge) and the total negative charge is –3 (from three chlorides, each with a –1 charge). Record the ionic charges in Columns 4 and 5 of the data table.

8. Write the formula for the ionic compound, using subscripts to indicate the number of each kind of ion used (from Columns 2 and 3). Follow the rules for writing ionic formulas listed in the background material. In our example, the formula is AlCl3. Record the chemical formula for the ionic compound in Column 6 of the data table.

9. Write the name of the ionic compound following the rules for naming ionic compounds discussed in the background infor-mation. In our example, the name of the compound is aluminum chloride. Record the name for the ionic compound in the last column of the data table.

10. Repeat steps 2 –7 for each set of combining ions in the data table.

Al3+

Cl–

Cl–

Cl–= AlCl3

– 3 –


11. After writing formulas for all 16 sets of combining ions listed in the data table, complete rows 17–20 of the data table by randomly choosing four more sets of combining ions (that have not already been combined). Follow the procedure in steps 2–7 to complete each column of the data table.

12. Gather the ion cards. Place them in an envelope and return the ion cards to the instructor.

Disposal

The Cards used in this activity may be saved and stored for future use.

Connecting to the National Standards

This laboratory activity relates to the following National Science Education Standards (1996):

Unifying Concepts and Processes: Grades K–12Systems, order, and organizationEvidence, models, and explanation

Content Standards: Grades 5–8Content Standard B: Physical Science, properties and changes of properties in matter, transfer of energy

Content Standards: Grades 9–12Content Standard B: Physical Science, structure and properties of matter, chemical reactions, interactions of energy and matter

Flinn Scientific—Teaching Chemistry™ eLearning Video Series

A video of the Putting Ions in Their Hands activity, presented by Peg Convery, is available in Covalent, Ionic and Metallic Bonding, part of the Flinn Scientific—Teaching Chemistry eLearning Video Series.

Materials for Putting Ions in Their Hands are available from Flinn Scientific, Inc.

Materials required to perform this activity are available in the Ionic Formula Writing Kit available from Flinn Scientific. Materials may also be purchased separately.

Catalog No. Description

AP4570 Ionic Formula Writing Kit

Consult your Flinn Scientific Catalog/Reference Manual for current prices.

– 4 – 91833

© 2009 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Covalent, Ionic and Metallic Bonding in the Flinn Scientific—Teaching Chemistry™ eLearning Video Series. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photo-copy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc.

Dat

a Ta

ble

Nam

e: _

____

____

____

____

____

____

____

____

____

____

___

Alu

min

um &

Chl

orid

e

Sodi

um &

Oxi

de

Iron

(II)

& S

ulfi

de

Pota

ssiu

m &

Sul

fate

Silv

er &

Nitr

ate

Cop

per(

II)

& H

ydro

xide

Am

mon

ium

& C

arbo

nate

Cop

per(

I) &

Pho

spha

te

Mag

nesi

um &

Bro

mid

e

Cal

cium

& A

ceta

te

Com

bini

ng I

ons

Num

ber

of c

atio

nsN

umbe

rof

ani

ons

Tota

l +ch

arge

Tota

l –ch

arge

For

mul

aN

ame

of c

ompo

und

91833


– 5 –

Dat

a Ta

ble

cont

inue

dN

ame:

___

____

____

____

____

____

____

____

____

____

____

_

Iron

(III

) &

Oxi

de

Cop

per(

I) &

Chr

omat

e

Sodi

um &

Bic

arbo

nate

Mag

nesi

um &

Pho

spha

te

Pota

ssiu

m &

Cya

nide

Alu

min

um &

Sul

fide

Com

bini

ng I

ons

91833


Ion Formula ChartNames and Charges of Some Common Ions

ammonium, NH4+

cesium, Cs+

copper(I), Cu+

gold(I), Au+

hydrogen, H+

lithium, Li+

potassium, K+

rubidium, Rb+

silver, Ag+

sodium, Na+

barium, Ba2+

beryllium, Be2+

cadmium, Cd2+

calcium, Ca2+

chromium(II), Cr2+

cobalt(II), Co2+

copper(II), Cu2+

iron(II), Fe2+

lead(II), Pb2+

magnesium, Mg2+

mercury(I), Hg22+

mercury(II), Hg2+

nickel, Ni2+

strontium, Sr2+

tin(II), Sn2+

zinc, Zn2+

aluminum, Al3+

chromium(III), Cr3+

cobalt(III), Co3+

gallium, Ga3+

gold(III) Au3+

iron(III), Fe3+

lead(IV), Pb4+

tin(IV), Sn4+

1+ 2+ 3+

acetate, C2H3O2–

bromate, BrO3–

bromide, Br–

chlorate, ClO3–

chloride, Cl–

chlorite, ClO2–

cyanide, CN–

dihydrogen

phosphate, H2PO4–

fluoride, F–

hydrogen carbonate,

or bicarbonate, HCO3–

hydrogen sulfate, HSO4–

hydroxide, OH–

iodate, IO3–

iodide, I–

nitrate, NO3–

nitrite, NO2–

permanganate, MnO4–

carbonate, CO32–

chromate, CrO42–

dichromate, Cr2O72–

hydrogen

phosphate, HPO42–

oxide, O2–

oxalate, C2O42–

peroxide, O22–

selenide, Se2–

sulfate, SO42–

sulfide, S2–

sulfite, SO32–

tartrate, C4H4O62–

telluride, Te2–

thiosulfate, S2O32–

borate, BO33–

nitride, N3–

phosphate, PO43–

phosphide, P3–

1– 2– 3–

4+

91833


Fe2+

Fe3+

Al3+

Fe3+

Al3+

Fe3+

Al3+

Ca2+

Fe2+ Fe2+ Mg2+ Mg2+ Mg2+

Ca2+ Ca2+ Cu2+ Cu2+ Cu2+

Na+

K+ K+ K+ Ag+ Ag+ Ag+

NH4+ NH4

+ NH4+ Cu+ Cu+ Cu+

Na+ Na+ Li+ Li+ Li+M

odel

s of

Cat

ions

91833


HCO3– HCO3

– HCO3–

CrO42– CrO4

2– CrO42–

PO43– PO4

3– PO43–

S2–

O2– O2– O2– CO32– CO3

2– CO32–

S2– S2– SO42– SO4

2– SO42–

Cl–

Br– Br– Br– C2H3O2– C2H3O2

– C2H3O2–

NO3– NO3

– NO3– CN– CN– CN–

Cl– Cl– OH– OH– OH–M

odel

s of

Ani

ons

– 9 –


Ans

wer

s to

Dat

a Ta

ble

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Alu

min

um &

Chl

orid

e

Al3+

and

Cl–

Sodi

um &

Oxi

de

Na+

and

O2–

Iron

(II)

& S

ulfi

de

Fe2+

and

S2–

Pota

ssiu

m &

Sul

fate

K+ a

nd S

O42–

Silv

er &

Nitr

ate

Ag+

and

NO

3–

Cop

per(

II)

& H

ydro

xide

Cu2+

and

OH

–

Am

mon

ium

& C

arbo

nate

NH

4+ a

nd C

O32–

Cop

per(

I) &

Pho

spha

te

Cu+

and

PO

43–

Mag

nesi

um &

Bro

mid

e

Mg2+

and

Br–

Cal

cium

& A

ceta

te

Ca2+

and

C2H

3O2–

Com

bini

ng I

ons

Num

ber

of c

atio

nsN

umbe

rof

ani

ons

Tota

l +ch

arge

Tota

l –ch

arge

For

mul

aN

ame

of c

ompo

und

1

3 +

3 –3

A

lCl 3

Alu

min

um c

hlor

ide

2

1 +

2 –2

N

a 2O

Sodi

um o

xide

1

1 +

2 –2

Fe

S Ir

on(I

I) s

ulfi

de

2

1 +

2 –2

K

2SO

4 Po

tass

ium

sul

fate

1

1 +

1 –1

A

gNO

3 Si

lver

nitr

ate

1

2 +

2 –2

C

u(O

H) 2

Cop

per(

II)

hydr

oxid

e

2

1 +

2 –2

(N

H4)

2CO

3 A

mm

oniu

m c

arbo

nate

3

1 +

3 –3

C

u 3PO

4 C

oppe

r(I)

pho

spha

te

1

2 +

2 –2

M

gBr 2

Mag

nesi

um b

rom

ide

1

2 +

2 –2

C

a(C

2H3O

2)2

Cal

cium

ace

tate

– 10 –


11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

Iron

(III

) &

Oxi

de

Fe3+

and

O2–

Cop

per(

I) &

Chr

omat

e

Cu+

and

CrO

42–

Sodi

um &

Bic

arbo

nate

Na+

and

HC

O3–

Mag

nesi

um &

Pho

spha

te

Mg2+

and

PO

43–

Pota

ssiu

m &

Cya

nide

K+ a

nd C

N–

Alu

min

um &

Sul

fide

Al3+

and

S2–

Com

bini

ng I

ons

Num

ber

of c

atio

nsN

umbe

rof

ani

ons

Tota

l +ch

arge

Tota

l –ch

arge

For

mul

aN

ame

of c

ompo

und

2

3 +

6 –6

Fe

2O3

Iron

(III

) ox

ide

2

1 +

2 –2

C

u 2CrO

4 C

oppe

r(I)

chr

omat

e

1

1 +

1 –1

N

aHC

O3

Sodi

um b

icar

bona

te

3

2 +

6 –6

M

g 3(PO

4)2

Mag

nesi

um p

hosp

hate

1

1 +

1 –1

K

CN

Po

tass

ium

cya

nide

2

3 +

6 –6

A

l 2S3

Alu

min

um s

ulfi

de

Ans

wer

s to

Dat

a Ta

ble

cont

inue

d

Documents

91833 Putting Ions in Their · PDF fileFlinn Scientific—Teaching Chemistry eLearning Video Series eLearning 2009 91833 011509 Publication No. 91833 Putting Ions in Their Hands Covalent,