1General Periodic General Periodic TrendsTrends

• Atomic and ionic size Atomic and ionic size

• Ionization energyIonization energy

• ElectronegativityElectronegativity

Higher effective nuclear chargeElectrons held more tightly

Larger orbitals.Electrons held lesstightly.

• CationCation• AnionAnion

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Atomic SizeAtomic SizeAtomic SizeAtomic Size

• Size goes UPSize goes UP on on going down a group. going down a group.

• Because electrons are Because electrons are added further from added further from the nucleus, there is the nucleus, there is less attraction. This is less attraction. This is due to additional due to additional energy levels and the energy levels and the shielding effectshielding effect. .

• Size goes UPSize goes UP on on going down a group. going down a group.

• Because electrons are Because electrons are added further from added further from the nucleus, there is the nucleus, there is less attraction. This is less attraction. This is due to additional due to additional energy levels and the energy levels and the shielding effectshielding effect. .

Each additional energy Each additional energy level “shields” the level “shields” the electrons from being electrons from being pulled in toward the pulled in toward the nucleus.nucleus.Size goes DOWN Size goes DOWN on on going across a period.going across a period.

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Atomic SizeAtomic SizeAtomic SizeAtomic Size

Size Size decreasesdecreases across a period across a period owing to increase in the positive owing to increase in the positive charge from the protons. Each added charge from the protons. Each added electron feels a greater and greater + electron feels a greater and greater + charge because the protons are pulling charge because the protons are pulling in the same direction, where the in the same direction, where the electrons are scattered.electrons are scattered.

LargeLarge SmallSmall

4

Which is Bigger?Which is Bigger?

• Na or K ?Na or K ?

• Na or Mg ?Na or Mg ?

• Al or I ?Al or I ?

5

IONIC RADII

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Ion SizesIon SizesIon SizesIon Sizes

Li,152 pm3e and 3p

Li+, 60 pm2e and 3 p

+Does the size goDoes the size goup or down up or down when losing an when losing an electron to form electron to form a cation?a cation?

Does the size goDoes the size goup or down up or down when losing an when losing an electron to form electron to form a cation?a cation?

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Ion SizesIon SizesIon SizesIon Sizes

• CATIONSCATIONS are are SMALLERSMALLER than the than the atoms from which they come.atoms from which they come.

• The electron/proton attraction has The electron/proton attraction has gone UP and so size gone UP and so size DECREASESDECREASES..

Li,152 pm3e and 3p

Li +, 78 pm2e and 3 p

+Forming Forming a cation.a cation.Forming Forming a cation.a cation.

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Ion SizesIon SizesIon SizesIon Sizes

F,64 pm9e and 9p

F- , 136 pm10 e and 9 p

-Does the size go up or Does the size go up or down when gaining an down when gaining an electron to form an electron to form an anion?anion?

Does the size go up or Does the size go up or down when gaining an down when gaining an electron to form an electron to form an anion?anion?

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Ion SizesIon SizesIon SizesIon Sizes

• ANIONSANIONS are are LARGERLARGER than the atoms from than the atoms from which they come.which they come.

• The electron/proton attraction has gone DOWN The electron/proton attraction has gone DOWN and so size and so size INCREASESINCREASES..

• Trends in ion sizes are the same as atom sizes. Trends in ion sizes are the same as atom sizes.

Forming Forming an anion.an anion.Forming Forming an anion.an anion.F, 71 pm

9e and 9pF-, 133 pm10 e and 9 p

-

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Trends in Ion SizesTrends in Ion SizesTrends in Ion SizesTrends in Ion Sizes

Figure 8.13Figure 8.13

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Which is Bigger?Which is Bigger?

• Cl or ClCl or Cl-- ? ?

• KK++ or K ? or K ?

• Ca or CaCa or Ca+2+2 ? ?

• II-- or Br or Br-- ? ?

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Mg (g) + Mg (g) + 738 kJ738 kJ ---> Mg ---> Mg++ (g) + e- (g) + e-

This is called the FIRST This is called the FIRST ionization energy because ionization energy because

we removed only the we removed only the OUTERMOST electronOUTERMOST electron

MgMg+ + (g) + (g) + 1451 kJ1451 kJ ---> Mg ---> Mg2+2+ (g) + e- (g) + e-This is the SECOND IE.This is the SECOND IE.

IE = energy required to remove an electron IE = energy required to remove an electron from an atom (in the gas phase).from an atom (in the gas phase).

Ionization EnergyIonization EnergyIonization EnergyIonization Energy

13Trends in Ionization Trends in Ionization EnergyEnergy

Trends in Ionization Trends in Ionization EnergyEnergy

• IE increases across a IE increases across a period because the period because the positive charge increases.positive charge increases.

• Metals loseMetals lose electrons electrons more easily than more easily than nonmetals.nonmetals.

•NonmetalsNonmetals lose lose electrons with electrons with difficulty (they like difficulty (they like to to GAIN GAIN electrons).electrons).

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Trends in Ionization Trends in Ionization EnergyEnergy

Trends in Ionization Trends in Ionization EnergyEnergy

• IE increases UP a IE increases UP a group group

• Because size Because size increases (Shielding increases (Shielding

Effect)Effect)

15

Which has a higher 1st ionization energy?

• Mg or Ca ?

• Al or S ?

• Cs or Ba ?

16

Electronegativity, Electronegativity,

is a measure of the ability of an atom is a measure of the ability of an atom in a molecule to attract electrons to in a molecule to attract electrons to itself.itself.

Concept proposed byConcept proposed byLinus PaulingLinus Pauling1901-19941901-1994

Concept proposed byConcept proposed byLinus PaulingLinus Pauling1901-19941901-1994

17Periodic Trends: Electronegativity

• In a group: Atoms with fewer energy levels can attract electrons better (less shielding). So, electronegativity increases UP a group of elements.

• In a period: More protons, while the energy levels are the same, means atoms can better attract electrons. So, electronegativity increases RIGHT in a period of elements.

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ElectronegativityElectronegativity

19

Which is more electronegative?

•F or Cl ?

•Na or K ?

•Sn or I ?

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The End !!!!!!!!!!!!!!!!!!!