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ChemActivity

24

The Bond-Type Triangle (What Type of Bonding is Present?)

Model 1: The Relationships Between Electronegativities and the Physical Properties of Compounds and Metals. Properties of Compounds with Ionic Bonding: • high melting points (usually >500 °C) • hard and brittle as solids • do not conduct electricity as solids; conduct electricity when molten Properties of Metals: • good conductors of electricity as solids • malleable and ductile as solids • melting points can be low (Hg, –39 °C) or high (W, 3410 °C) Properties of Compounds with Covalent Bonding: • melting points can be low (H2, < –252 °C) or high (C, diamond, > 3000 °C) • variable hardness • do not conduct electricity as solids or when molten Table 1.

Electronegativity, EN, parameters and melting points for selected compounds. Melting Type of Compound ∆EN EN or Metal Point Bonding first second (°C) atom atom CsF(s) 0.66 4.19 2.42 3.53 682 ionic NaCl(s) 0.87 2.87 1.87 2.00 801 ionic NaI(s) 0.87 2.36 1.62 1.49 661 ionic Cs(s) Na(s) CuZn(s; brass)

0.66 0.87 1.8

0.66 0.87 1.6

0.66 0.87 1.7

0 0 0.2

F2(g) CH4(g) C(s; diamond)

4.19 2.54 2.54

4.19 2.30 2.54

4.19 2.42 2.54

0 0.24 0

28 98 932

metallic metallic metallic

–220 –182 >3000

covalent covalent covalent

HI(g) 2.30 2.36 –51 GaAs(s) 1.76 2.21 1238 Si(s) 1.92 1.92 1.92 0 1410 __ EN is the average electronegativity of the two elements. ∆EN is the (absolute) difference in electronegativity between the two elements.

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ChemActivity 24

The Bond-Type Triangle

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Critical Thinking Questions 1. Use the data from Table 1 to complete the table below. Type of bonding Ionic

__ Range for EN

Range for ∆EN

1.62 – 2.42

Metallic

0 – 0.2

Covalent 2. Individually answer the two parts below. Then compare your answer with the other members of your team, come to consensus answers, and add your team’s responses to Table 1. __ a) Determine the ∆EN value and the EN value for HI.

b)

3.

a)

__ Determine the ∆EN value and the EN value for GaAs.

Based on the data in Table 1 and your answers to CTQs 1 and 2a, is it possible to classify HI as having metallic, ionic, or covalent bonding? Yes

b)

(circle)

Explain your reasoning.

Based on the data in Table 1 and your answers to CTQs 1 and 2b, is it possible to classify GaAs as having metallic, ionic, or covalent bonding? Yes

c)

No

No

(circle)

Explain your reasoning.

Based on your answer to CTQ 1 and the information in Table 1, is it possible to classify Si as having metallic, ionic, or covalent bonding? Yes

No

(circle)

Explain your reasoning.

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ChemActiivity 24

The Bond-Type Triangle

Mod del 2: The Bond-T Type Triangle. A bond-typee triangle iss a graph that enabless us to preddict the pro operties of a comp pound baseed on the electronegaativities of the elemeents that comprise c t he h comp pound. Thee data for CsF, C F 2, and d Cs from Table T 1 havve been used d to generatte threee points at tthe corners of the bond-type trianngle shown in Figure 1. 1 The bond dtype triangle ca an be divided into reggions that indicate th e predominant n type of o ding present in compou unds. The dividing d lines between regions r are not n absolutee, bond but they give a general g idea of the boun ndaries betw ween differeent types of bonding. M Many comp pounds have propertiees that are intermediatte between those of th he threee main bond d types: me tallic, t covalent, and ion nic. The sem mimetal Si, for exampl ee, is kn nown to be a semiconductor; this material haas properti es e that are intermedia te t between metallic c and covaleent. ure 1. Figu

A bond-type e triangle.

Critical Thinking Que estions 6.

a)

Ver ify that t he points f o r CsF, F2 , and Cs are at the appropriatte posiitions on t he bond-typee triangle.

b)

Exp p lain why th he corners of o the bondd-type triangle are defi ned by CsF F, F2, and Cs.

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ChemActivity 24

The Bond-Type Triangle

155

7. Place a point on the chart for: a)

sodium chloride, a compound with ionic bonding

b)

sodium, a metal

c)

methane, CH4, a compound with covalent bonding

d)

Si, a semimetal

8. Associate the regions (A, B, C) with bond types (metallic, covalent, ionic). The "SM" region refers to semimetals.

9. Use the data in Table 1 and the bond-type triangle in Figure 1 to predict the type of bonding present in HI and GaAs.

10.

Quartz, SiO2, is a very high melting, hard solid. Place a point for SiO2 on the bond-type triangle. (Recall that the EN for O is 3.61.) What type of bonding would you predict to be predominant in quartz?

Exercises 1. For each of the following compounds, place a point on the bond-type triangle. Classify each compound as metallic, covalent, ionic, semimetal. a) CO2

b) NH3

c) BaO

d) SO2

e) AlSb

f) GaAs

g) CdLi

h) BaBr2

i) ZnO

j) NaH

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ChemActivity 24

The Bond-Type Triangle

2. Suggest a binary compound which would have the following characteristic [one compound for a), one compound for b), etc.]: a)

conducts electricity in the solid state

b)

has a high melting point and is an insulator

c)

has a low melting point and is an insulator

d)

has a high melting point and conducts electricity in the solid state

e)

has a low melting point and conducts electricity in the solid state

f)

is a semiconductor

3. What type of bonding will each of the following compounds exhibit? a)

A binary compound with a low

b)

A binary compound with a high

and a low ∆EN. and a low ∆EN.

Problems 1. Answer the following electronegativities.

question

without

referring

to

a

table

of

In the bond-type triangle below, the position of the compound SnI4 is indicated with an arrow. Which point (A, B, C, or D) is most likely to correspond to AgCl? Explain your reasoning clearly.

∆

2. Give the type of bonding in each of the following: CaSO4(s); NaClO4(s).

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CO32–; BaCO3(s);...