What Causes the Periodic Trends in Properties

Sample Problem 7.6 illustrates how Coulomb s law can be used to compare the magnitudes of attractive forces between charged objects. 

Attractive I oicc between Oppositely Cliaigcd Objects at a Fixed Distance cl = 1) from Each Otiicr 

The product of a positive number and a negative number is a negative number. When we are simply comparing the magnitudes of attractive forces, however, it is unnecessary to include the sign. 

Strategy Use Coulomb s law to calculate a number to which the attractive force will be proportional in each case. 

Note that in this type of comparison, it doesn t matter what units we use for the distance between the charges. We are not trying to calculate a particular attractive force, only to compare the magnitudes of these two attractive forces. 

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