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Periodic Properties of theElements

Part I

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Mendeleev’s Original Periodic Table

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Isoelectronic (Series)

Species having the same ground-stateelectron configuration are isoelectronic 

Ex:

Mg2+, F-, Na+, Ne, Al3+, O2-, N3-

All the above species are part of the sameisoelectronic series

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Periodicity:

Properties of elements repeat and vary

depending on their location in the periodictable

• Effective Nuclear Charge•  Atomic Radius

• Ionic Radius

• Ionization Energy (I 1, I 

2 , …)

• Electron Affinity 

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Effective Nuclear Charge

Zeff  : the positive charge (from nucleus) feltby an electron

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☼ Zeff 

is the result of opposing forces

☼ As Zeff 

increases, e- will experience greater 

attraction to the nucleus

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☼ Use Zeff 

estimates to compare elements

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Ex:

Ne 1s2

2s2

2p6

 

shield e-

outermost e-

10 p+

4 e-

Zeff  = Z – S = – = +6

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Ex:

F 1s2

2s2

2p5

 

shield e-

outermost e-

9 p+

4 e-

Zeff  = Z – S = – = +5

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Effective nuclear charge

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Zeff  Ne > Zeff  F

• Equal e- shielding

• Ne has more protons than F

• Ne outermost e- experience greater attractive force

towards the nucleus

☼ the strength of attraction between theoutermost e-  and the nucleus determinesan atom’s periodic properties

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Atomic Radius

•One-half the distance between two adjacent nuclei

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Atomic radius decreases across the periodictable to the right.

Atomic radius increases as you go down the

table.

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☼ As Zeff  decreases, atomic radius

increases (e- are held with less force

thus farther from the nucleus)

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Ex: Atomic radius of K > Ca. Why?

K 1s2 2s2 2p6 3s2 3p6 4s1

 18 e-

Zeff  = – = +1

19 p+

Ca 1s2 2s2 2p6 3s2 3p6 4s2

Zeff  = 20 – 18 = +2 

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K > Ca

• Equal e-

shielding• Ca has one more proton than K

• Zeff  Ca > Zeff  K

• Ca outermost e- experience more attractive force towards

the nucleus

☼ Ca outermost e-  are pulled closer to thenucleus than those of K

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Ionic Radii- Cations•

radius decreases due to an increase in Zeff 

•Cations are smaller than their parent atom

Ca 1s2 2s2 2p6 3s2 3p6 4s2

Zeff  = – =20 18 +212 +8

2+

Zeff  Ca < Zeff  Ca2+

Ca2+ is smaller than Ca

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Ionic Radii- Anions

• radius increases due to crowding of more e- 

into a subshell

• additional repulsion between e- forces them

farther from nucleus

• Anions are larger than their parent atom

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Ex: Rank the following isoelectronic series in

order of decreasing size:

Rb1+, Sr 2+, Se2-, Br 1-

Se2- > Br 1- > Rb1+ > Sr 2+

Rb1+ Zeff  = 37 - 30 = +7

Sr 2+ Zeff  = 38 - 30 = +8

Se2- Zeff  = 34 - 30 = +4

Br 1-

Zeff  = 35 - 30 = +5

Ionization Energy

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Ionization Energy

• Minimum energy required to remove

the outermost electron form an isolatedneutral atom in the gaseous state.

• kJ/mol

• X(g) X+(g) + e

- 

• ∆H = I1 (1st Ionization Energy)

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Why?

☼ As Zeff 

increases, e- are held with more

force

☼ As attractive force increases, more

energy is required to remove an e-

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break

HW: p. 339 # 82, 85, 86p. 340 # 87, 88, 90

LP: Lab 9 (both parts)