Periodic TrendsPeriodic TrendsElectron Electron AffinityAffinity

Electron AffinityElectron Affinity►The energy change that The energy change that occurs when an atom occurs when an atom gains an electrongains an electron►How much an atom How much an atom “likes” to gain electrons“likes” to gain electrons

I love electrons!!

►Atoms with a Atoms with a high attractionhigh attraction for for electrons will have electrons will have more negativemore negative values for their Electron Affinityvalues for their Electron Affinity

Compare K and F based on Compare K and F based on Electron Affinity:Electron Affinity:

►F’s value for EA will be more F’s value for EA will be more negative than K’s because we know negative than K’s because we know that F wants to gain an electron that F wants to gain an electron whereas K wants to lose an electron.whereas K wants to lose an electron.

Electron AffinitiesElectron Affinities(Main Group Elements)(Main Group Elements)

HH-73-73LiLi

-60-60NaNa-53-53KK

-48-48RbRb-47-47

BeBe1919MgMg1919CaCa-2-2SrSr-5-5

BB-27-27

CC--

122122

NN77

OO--

141141

FF--

328328

NeNe2929

AlAl-43-43

SiSi--

134134

PP-72-72

SS--

200200

ClCl--

349349

ArAr3535

CaCa-30-30

GeGe--

119119

AsAs-78-78

SeSe--

195195

BrBr--

325325

KrKr3939

InIn-30-30

SnSn--

107107

SbSb--

103103

TeTe--

190190

II--

295295

XeXe4141

He 21

Generally increasing Electron Affinity

Generally increasing Electron Affi

nity

Things to Note:Things to Note:►The Noble Gases have positive The Noble Gases have positive

EA meaning they DO NOT WANT EA meaning they DO NOT WANT TO GAIN AN ELECTRONTO GAIN AN ELECTRON

►The Halogens (Group 7A) have The Halogens (Group 7A) have the largest (most negative) EA the largest (most negative) EA because they only need one because they only need one electron to have the electron electron to have the electron configuration of a noble gasconfiguration of a noble gas

►Both of the above are due to the Both of the above are due to the Octet RuleOctet Rule

Octet RuleOctet RuleAtoms tend to gain, lose, or Atoms tend to gain, lose, or share electrons in order to have share electrons in order to have a set of 8 electrons in their a set of 8 electrons in their valence (outermost) energy valence (outermost) energy level (except for elements in level (except for elements in the first energy level, they want the first energy level, they want 2 in their valence energy level)2 in their valence energy level)

How to rank Electron How to rank Electron Affinities:Affinities:

►Noble gases will always have the lowest Noble gases will always have the lowest electron affinities (positive values)electron affinities (positive values)

►Nonmetals will have the higher electron Nonmetals will have the higher electron affinities (more negative values) than affinities (more negative values) than metalsmetals

►When comparing two nonmetals, the one When comparing two nonmetals, the one that is closest to becoming a noble gas that is closest to becoming a noble gas will have the higher Electron Affinitywill have the higher Electron Affinity If in the same group, the smaller one will If in the same group, the smaller one will

have the higher electron affinityhave the higher electron affinity

Na or Cl?Na or Cl?Which has the higher EA (more Which has the higher EA (more

negative value)negative value)►Cl Cl ►Because Cl is a nonmetal and Because Cl is a nonmetal and

it only needs one more it only needs one more electron whereas Na needs to electron whereas Na needs to lose an electron so gaining one lose an electron so gaining one would not be helpful!would not be helpful!

Ne or Br?Ne or Br?Which one will have the smaller Which one will have the smaller

EA (least negative value)EA (least negative value)►NeNe►Ne is a noble gas so it will Ne is a noble gas so it will

always have the smallest always have the smallest Electron AffinityElectron Affinity

O or F?O or F?Which has the largest EA?Which has the largest EA?

►Remember, largest EA = more Remember, largest EA = more negative valuenegative value

►Answer: FAnswer: F►Because both are nonmetals but Because both are nonmetals but

fluorine is closer to becoming a fluorine is closer to becoming a noble gas (only has to gain one)noble gas (only has to gain one)

I or Cl?I or Cl?Which has a higher EA?Which has a higher EA?

►ClCl►They are both nonmetals and They are both nonmetals and

are in the same group but Cl is are in the same group but Cl is smaller so it has a better ability smaller so it has a better ability to attract electrons to its to attract electrons to its nucleus since it is closer to the nucleus since it is closer to the valence levelvalence level