MondayNovember 1, 2010

(Periodicity in Atomic Radius)

Bell RingerMonday, 11-1-10

What is meant by the term “periodicity?”

Chemistry defines periodicity as similarities in chemical properties

recurring at regular intervals .

In general terms, periodicity is defined as the quality of recurring

at regular intervals .

This leads to the Periodic Law, which states that the physical and

chemical properties of the elements are periodic functions of

their atomic numbers.

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Date of Notes on Website

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WS: Atomic Structure

73-74 10/1 10/8

PeriodicityRemember from today’s Bell Ringer that chemistry defines periodicity as similarities in chemical properties

recurring at regular intervals .The Periodic Law states that the physical and chemical properties of

the elements are periodic functions of their atomic numbers.If you arrange the elements in

order of their atomic numbers (number of protons), similar

properties will appear at regula intervals.Recall the interval

sequence: 8,8, 18, 18, 32

Five Properties of Elements that Display Periodicity

Atomic RadiusIonization EnergyElectron Affinity

Ionic RadiusElectronegativity

Atomic RadiusAtomic radius may be defined as one-half the distance between the nuclei of identical atoms

that are bonded together.A picometer

(pm) is a metric unit of length equal

to one trillionth of a

meter.

1x10-12 meter

On your metric

staircase, this would be 9 steps below

milli-

Atomic RadiusAtomic radii decrease from left to right across a

period because of the increasing positive charge of the nuclei (more and more p+) pulling

the e- closer and closer.Generally

speaking, the size of the atoms get

smaller as you move from left to right across

a period.

smaller

Atomic RadiusAtomic radii increase from top to bottom down a group because of e- occupying sublevels in

successively higher main energy levels.

Generally speaking, the

size of the atoms get

larger as you move from top

to bottom down a group.

larger

Even thought the lines in each period are not identical, they show a similarity that creates a

pattern. This is NOT randomness!

WorksheetThe Periodic Law