Cliffs AP Chemistry, 3rd Edition

Part I: Introduction

The Bullet Format

The bullet format is also a very efficient technique because it, like the chart format, does not re-

quire complete sentences. In using this format, you essentially provide a list to answer the

question. A • is a bullet, and each new concept receives one. Try to add your bullets in a logical

sequence, and leave room to add more bullets. You may want to come back later and fill them

in. Don’t get discouraged if you do not have as many bullets as the samples contain — it takes

practice. Reviewing the key terms at the beginning of each chapter may suggest additional

points that you can incorporate.

Essay 2

As one examines the periodic table, one discovers that the melting points of the alkali

metals increase as one moves from cesium to lithium, whereas the melting points of the

halogens increase from fluorine to iodine.

A. Explain the phenomenon observed in the melting points of the alkali metals.

B. Explain the phenomenon observed in the melting points of the halogens.

C. Given the compounds CsI, NaCl, LiF, and KBr, predict the order of their melting

points (from high to low) and explain your answer using chemical principles.

Answer

2. Given — melting points: alkali metals increase from Cs →Li
   halogens increase from F →I

(a) Restatement: Explain alkali metal trend.

• Observed melting point order: Li > Na > K > Rb > Cs


• All elements are metals


• All elements contain metallic bonds


• Electrons are free to migrate in a “sea”


• As one moves down the group, size (radius) of the atoms increases


• As volume of atom increases, charge density decreases


• Attractive force between atoms is directly proportional to melting point


• Therefore, as attractive forces decrease moving down the group, melting point
  decreases

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