ghs honors chem section 14.2 periodic trends objectives: interpret group trends in atomic radii,...

GHS Honors ChemGHS Honors Chem

Section 14.2Section 14.2Periodic TrendsPeriodic Trends

OBJECTIVES:OBJECTIVES: Interpret Interpret group trendsgroup trends in atomic in atomic

radii, ionic radii, ionization radii, ionic radii, ionization energies, and electronegativities.energies, and electronegativities.

Interpret Interpret period trendsperiod trends in atomic in atomic radii, ionic radii, ionization radii, ionic radii, ionization energies, and electronegativities. energies, and electronegativities.


Trends in Atomic SizeTrends in Atomic Size

First problem: Where do you First problem: Where do you start measuring from?start measuring from?

The electron cloud doesn’t have The electron cloud doesn’t have a definite edge.a definite edge.

They get around this by They get around this by measuring more than 1 atom at measuring more than 1 atom at a time.a time.


Atomic SizeAtomic Size

Atomic Radius = half the distance between two nuclei Atomic Radius = half the distance between two nuclei of atomsof atoms in the solid state (by X-ray diffraction)in the solid state (by X-ray diffraction) or of a diatomic molecule.or of a diatomic molecule.

}RadiusRadius


Atomic Size Atomic Size Influenced by three factors:Influenced by three factors:1.1. Energy LevelEnergy Level

• Higher energy level is further away.Higher energy level is further away.

2.2. Charge on nucleusCharge on nucleus• More positive charge pulls electrons More positive charge pulls electrons

in closer.in closer.

3.3. Shielding effectShielding effect• The inner electrons shield the outer The inner electrons shield the outer

electrons from the nuclear electrons from the nuclear charge/attraction.charge/attraction.


ShieldingShielding The electron on the outermost The electron on the outermost

energy level has to look energy level has to look through all the other energy through all the other energy levels to see the nucleus.levels to see the nucleus.

Second electron has same Second electron has same shielding, if it is in the same shielding, if it is in the same periodperiod

Shielding Increases down a Shielding Increases down a Group, and is Constant across a Group, and is Constant across a Period.Period.

Shielding Across a Group is Shielding Across a Group is Constant, but the Constant, but the EFFECTIVE EFFECTIVE NUCLEAR CHARGE INCREASESNUCLEAR CHARGE INCREASES..


Group TrendsGroup Trends in Atomic in Atomic SizeSize

As we go down a group...As we go down a group... each atom has another each atom has another

energy level,energy level, so the atoms get bigger.so the atoms get bigger. Shielding increases as Shielding increases as

well, so the nucleus has well, so the nucleus has less of a hold on eless of a hold on e--… … distance is longer.distance is longer.

The Increased size of the The Increased size of the Energy Levels down a Energy Levels down a group outweighs the group outweighs the increased nuclear chargeincreased nuclear charge

HLi

Na

K

Rb


Periodic TrendsPeriodic Trends in Atomic Size in Atomic Size As you go across a period, the radius As you go across a period, the radius

gets smaller.gets smaller. Electrons are in Electrons are in same energy levelsame energy level.. More More nuclear chargenuclear charge.. Shielding is constant … not an issue.Shielding is constant … not an issue. Outermost electrons are closer.Outermost electrons are closer.

Na Mg Al Si P S Cl Ar


Atomic Atomic Radius Radius OverallOverall


Overall Overall Periodic Trend Periodic Trend

for Atomic for Atomic RadiiRadii

Atomic Number

Ato

mic

Rad

ius

(nm

)

H

Li

Ne

Ar

10

Na

K

Kr

Rb

Xe

He


Trends in Ionization EnergyTrends in Ionization Energy

The amount of energy required to The amount of energy required to completely remove an electron from completely remove an electron from a gaseous atom.a gaseous atom.

Removing one electron makes a 1+ Removing one electron makes a 1+ ion.ion.

The energy required to remove the The energy required to remove the first electron is called the first electron is called the first first ionization energy.ionization energy.


Ionization EnergyIonization Energy

The The secondsecond IE is the energy IE is the energy required to remove the second required to remove the second electron.electron.

Always greater than first IE.Always greater than first IE. The The thirdthird IE is the energy required IE is the energy required

to remove a third electron.to remove a third electron. Greater than 1st or 2nd IE.Greater than 1st or 2nd IE.


Symbol First Second Third

HHeLiBeBCNOF Ne

1312 2371 520900800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 35694619 4577530160456276

Ionization Energy TableIonization Energy TableWhere are the Group Where are the Group

Effects?Effects?

1A1A

2A2A

3A3A


HHeLiBeBCNO F Ne

1312 2371 520 900 800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 3569 4619 4577 5301 6045 6276

Symbol First Second Third

Can we See the Effect of Can we See the Effect of Nuclear Charge in this Nuclear Charge in this

Table?Table?


What Affects the IEWhat Affects the IE

The greater the nuclear charge, the The greater the nuclear charge, the greater the IE.greater the IE. Larger positive nucleus has a greater Larger positive nucleus has a greater

attraction for the electrons, so the IE attraction for the electrons, so the IE increases.increases.

Greater distance from nucleus decreases Greater distance from nucleus decreases IEIE Electrons are further away from the Electrons are further away from the

attractive nucleus, and are easier to remove.attractive nucleus, and are easier to remove.


What Affects the IEWhat Affects the IE

Filled and half-filled orbitals have Filled and half-filled orbitals have lower energy, so the removal of an lower energy, so the removal of an electron to achieve this ½ filled electron to achieve this ½ filled orbital requires unusually low IE.orbital requires unusually low IE.

Shielding effectShielding effect As Shielding increases, it is easier to “pluck” As Shielding increases, it is easier to “pluck”

the outer electron, so the IE would decrease.the outer electron, so the IE would decrease.

Let’s look at Group & Period Trends for IELet’s look at Group & Period Trends for IE


Group trends on IEGroup trends on IE

As you go down a group, As you go down a group, first IE decreases first IE decreases because...because...

The electron is further The electron is further away.away.

More shielding.More shielding.

H1

Li3

Na11

K19

Rb37

Cs55

Fr87


Periodic trends on IEPeriodic trends on IE

Across the representative elements, the Across the representative elements, the atoms are in the same period & have the atoms are in the same period & have the same energy level.same energy level.

Same shielding.Same shielding. But, increasing nuclear charge holds eBut, increasing nuclear charge holds e--’s ’s

tighter.tighter. So IE generally increases from left to right.So IE generally increases from left to right. Exceptions at full and 1/2 full orbitals.Exceptions at full and 1/2 full orbitals.


1st Ionizatio

n Energy Increases

Summarizing 1Summarizing 1stst Ionization Ionization EnergyEnergy


Firs

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Atomic numberAtomic number

HeHe

He has a greater He has a greater IE than H.IE than H.

same shielding same shielding greater nuclear greater nuclear

chargecharge

HH

First Ionization EnergyFirst Ionization Energy


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HH

HeHe Li has lower IE Li has lower IE

than Hthan H more shielding more shielding further awayfurther away these outweigh these outweigh

greater nuclear greater nuclear chargecharge LiLi



Firs

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HH

HeHe

Be has higher IE Be has higher IE than Lithan Li

same shielding same shielding greater nuclear greater nuclear

chargecharge

LiLi

BeBe



Firs

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HH

HeHe B has lower IE B has lower IE

than Bethan Be same shielding same shielding greater nuclear greater nuclear

chargecharge By removing an By removing an

electron we make electron we make the s orbital half-the s orbital half-filledfilled

LiLi

BeBe

BB



Firs

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gyF

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ergy


HH

HeHe

LiLi

BeBe

BB

CC



Firs

t Ion

izat

ion

ener

gyF

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oniz

atio

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ergy


HH

HeHe

LiLi

BeBe

BB

CC

NN



Firs

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ion

ener

gyF

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HH

HeHe

LiLi

BeBe

BB

CC

NN

OO

Breaks the Breaks the pattern, pattern, because because removing an removing an electron electron leaves 1/2 leaves 1/2 filled p orbitalfilled p orbital



Firs

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ener

gyF

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HH

HeHe

LiLi

BeBe

BB

CC

NN

OO

FF



Firs

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ener

gyF

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oniz

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ergy


HH

HeHe

LiLi

BeBe

BB

CC

NN

OO

FF

NeNe Ne has a Ne has a

lower IE than lower IE than HeHe

Both are full,Both are full, Ne has more Ne has more

shieldingshielding Greater Greater

distancedistance



Firs

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izat

ion

ener

gyF

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HH

HeHe

LiLi

BeBe

BB

CC

NN

OO

FF

NeNe Na has a Na has a lower IE than lower IE than LiLi

Both are sBoth are s11

Na has more Na has more shieldingshielding

Greater Greater distancedistanceNaNa



Firs

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gyF

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ergy


HeHe

LiLi

NeNe

NaNa

ArAr

KrKr

KK



What’s the Driving Force?What’s the Driving Force?

Full Energy Levels require lots of Full Energy Levels require lots of energy to remove their energy to remove their electrons.electrons.

Noble Gases have full orbitals.Noble Gases have full orbitals. Atoms behave in ways to achieve Atoms behave in ways to achieve

noble gas configuration.noble gas configuration.


2nd2nd Ionization Energy Ionization Energy

For elements that reach a filled For elements that reach a filled or half-filled orbital by removing or half-filled orbital by removing 2 electrons, 2nd IE is lower than 2 electrons, 2nd IE is lower than expected.expected.

True for sTrue for s2 2

Alkaline earth metals form 2+ Alkaline earth metals form 2+ ions.ions.


Using the same logic sUsing the same logic s22pp11 atoms atoms

have a low 3rd IE.have a low 3rd IE. Atoms in the aluminum family Atoms in the aluminum family

form 3+ ions.form 3+ ions. 2nd IE and 3rd IE are always 2nd IE and 3rd IE are always

higher than 1st IE!!!higher than 1st IE!!!

3rd3rd Ionization Energy Ionization Energy


Trends in Electron AffinityTrends in Electron Affinity

What is Electron Affinity?What is Electron Affinity?

It’s the energy change It’s the energy change associated with associated with addingadding an an

electronelectron to a gaseous to a gaseous atom.atom.


Trends in Electron AffinityTrends in Electron Affinity

It’s easiest to add an electron to It’s easiest to add an electron to Group 7A.Group 7A.

It gets them to a full energy level, It gets them to a full energy level, or completes the or completes the OCTETOCTET..

Increase from left to right: atoms Increase from left to right: atoms become smaller, with greater become smaller, with greater nuclear charge.nuclear charge.

Decrease as we go down a group.Decrease as we go down a group.


Electron Affinity in the Periodic Electron Affinity in the Periodic TableTable


Electron Affinity in 3-DElectron Affinity in 3-D


Trends in Ionic SizeTrends in Ionic Size

Cations form by Cations form by losinglosing electrons. electrons. Cations are smaller that the atom Cations are smaller that the atom

they come from.they come from. Metals form cations.Metals form cations. Cations of representative elements Cations of representative elements

have noble gas configuration.have noble gas configuration.


Anions form by Anions form by gaininggaining electrons. electrons. Anions are bigger that the atom Anions are bigger that the atom

they come from.they come from. Nonmetals form anions.Nonmetals form anions. Anions of representative elements Anions of representative elements

have noble gas configuration.have noble gas configuration.

Trends in Ionic SizeTrends in Ionic Size


Revisiting Configuration of IonsRevisiting Configuration of Ions

Ions always have noble gas Ions always have noble gas configuration.configuration.

Na is: 1sNa is: 1s222s2s222p2p663s3s11 Forms a 1+ ion: 1sForms a 1+ ion: 1s222s2s222p2p66 Same configuration as Neon.Same configuration as Neon. Metals form ions with the configuration Metals form ions with the configuration

of the noble gas before them - they of the noble gas before them - they lose electrons.lose electrons.


Non-metals form ions by gaining Non-metals form ions by gaining electrons to achieve noble gas electrons to achieve noble gas configuration.configuration.

They end up with the They end up with the configuration of the noble gas configuration of the noble gas after them.after them.

Revisiting Configuration of IonsRevisiting Configuration of Ions


Group TrendsGroup Trends Going down a Going down a

Group, you are Group, you are adding energy adding energy levelslevels

Ions get bigger as Ions get bigger as you go down.you go down.

Li1+

Na1+

K1+

Rb1+

Cs1+


Periodic TrendsPeriodic Trends Across the period, nuclear charge Across the period, nuclear charge

increases so they get smaller.increases so they get smaller. Energy level changes between anions Energy level changes between anions

and cations.and cations.

Li1+

Be2+

B3+

C4+

N3-O2- F1-


Size of Isoelectronic ionsSize of Isoelectronic ions

Iso- means the sameIso- means the same Iso electronic ions have the same Iso electronic ions have the same

# of electrons# of electrons AlAl3+3+ Mg Mg2+ 2+ NaNa1+ 1+ Ne FNe F1- 1- OO2- 2- and Nand N3-3-

all have 10 electronsall have 10 electrons all have the configuration: all have the configuration:

1s1s222s2s222p2p66


Size of Isoelectronic ionsSize of Isoelectronic ions Positive ions that have more protons would be Positive ions that have more protons would be

smaller.smaller. Increase in size from most positive to most negativeIncrease in size from most positive to most negative

Al3+

Mg2+

Na1+ Ne F1- O2- N3-


ElectronegativityElectronegativity The tendency for an atom to The tendency for an atom to attract attract

electrons to itself when it is electrons to itself when it is chemically chemically combined combined with another element.with another element.

How fair is the sharing?How fair is the sharing? Big electronegativity means it pulls the Big electronegativity means it pulls the

electron towards it.electron towards it. Atoms with large negative electron Atoms with large negative electron

affinity have larger electronegativity.affinity have larger electronegativity.


Electronegativity Group TrendElectronegativity Group Trend

The further down a group, the farther the electron The further down a group, the farther the electron is away, and the more electrons an atom has.is away, and the more electrons an atom has.

Pull/Attraction of the positive nucleus is lessened Pull/Attraction of the positive nucleus is lessened due to increased distance and Shielding.due to increased distance and Shielding.

Electronegativity decreases.Electronegativity decreases. More willing to share. More willing to share.


Electronegativity Period TrendElectronegativity Period Trend

As you move across a Period, there are the As you move across a Period, there are the same number of energy levels, the same same number of energy levels, the same shielding, however …shielding, however …

Pull/Attraction of the positive nucleus on other’s Pull/Attraction of the positive nucleus on other’s electrons increases as the nucleus gets largerelectrons increases as the nucleus gets larger

Electronegativity Increases.Electronegativity Increases.


Electronegativity Periodic Electronegativity Periodic TrendTrend

Metals are at the left of the table.Metals are at the left of the table. They let their electrons go easilyThey let their electrons go easily Low electronegativityLow electronegativity At the right end are the nonmetals.At the right end are the nonmetals. They want more electrons.They want more electrons. Try to take them away from othersTry to take them away from others High electronegativity.High electronegativity.


Electronegativity in 3-DElectronegativity in 3-D


Ionizatio

n Energy,

Electronegativ

ity, a

nd Electron

Affinity Increases

Can We Possibly Summarize all Can We Possibly Summarize all of this Stuff???of this Stuff???


Atomic size & Ionic Size

Atomic size & Ionic Size

Increases

Increases



Shielding is constantShielding is constant


Shi

eldi

ng I

ncre

ases

Shi

eldi

ng I

ncre

ases

ghs honors chem section 14.2 periodic trends objectives: interpret group trends in atomic radii,...

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