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Chapter 7Chapter 7

Atomic StructureAtomic Structure

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Periodic TrendsPeriodic Trends Ionization energy the energy required to Ionization energy the energy required to

remove an electron form a gaseous atomremove an electron form a gaseous atom Highest energy electron removed first. Highest energy electron removed first. First ionization energy (First ionization energy (II11) is that ) is that

required to remove the first electron.required to remove the first electron. Second ionization energy (Second ionization energy (II22) - the ) - the

second electronsecond electron etc. etc.etc. etc.

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Trends in ionization energyTrends in ionization energy for Mg for Mg

• II11 = 735 kJ/mole = 735 kJ/mole

• II22 = 1445 kJ/mole = 1445 kJ/mole

• II33 = 7730 kJ/mole = 7730 kJ/mole The effective nuclear charge increases as The effective nuclear charge increases as

you remove electrons.you remove electrons. It takes much more energy to remove a It takes much more energy to remove a

core electron than a valence electron core electron than a valence electron because there is less shieldingbecause there is less shielding

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Explain this trendExplain this trend For AlFor Al

• II11 = 580 kJ/mole = 580 kJ/mole

• II22 = 1815 kJ/mole = 1815 kJ/mole

• II33 = 2740 kJ/mole = 2740 kJ/mole

• II44 = 11,600 kJ/mole = 11,600 kJ/mole

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Across a PeriodAcross a Period Generally from left to right, Generally from left to right, II11

increases because increases because there is a greater nuclear charge with there is a greater nuclear charge with

the same shielding.the same shielding. As you go down a group As you go down a group II11

decreases because electrons are decreases because electrons are further away and there is more further away and there is more shieldingshielding

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It is not that simpleIt is not that simple ZZeffeff changes as you go across a changes as you go across a

period, so will period, so will II11

Half-filled and filled orbitals are Half-filled and filled orbitals are harder to remove electrons fromharder to remove electrons from

here’s what it looks likehere’s what it looks like

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Firs

t Ion

izat

ion

ener

gy

Atomic number

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Firs

t Ion

izat

ion

ener

gy

Atomic number

9

Firs

t Ion

izat

ion

ener

gy

Atomic number

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Atomic SizeAtomic Size First problem where do you start First problem where do you start

measuringmeasuring The electron cloud doesn’t have a The electron cloud doesn’t have a

definite edge.definite edge. They get around this by measuring They get around this by measuring

more than 1 atom at a timemore than 1 atom at a time

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Atomic SizeAtomic Size

Atomic Radius = half the distance between Atomic Radius = half the distance between two nuclei of a diatomic moleculetwo nuclei of a diatomic molecule

}Radius

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Trends in Atomic Size Trends in Atomic Size Influenced by two factorsInfluenced by two factors ShieldingShielding More shielding is further awayMore shielding is further away Charge on nucleusCharge on nucleus More charge pulls electrons in More charge pulls electrons in

closercloser

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Group trendsGroup trends As we go down a As we go down a

groupgroup Each atom has Each atom has

another energy another energy levellevel

So the atoms get So the atoms get biggerbigger

HLi

Na

K

Rb

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Periodic TrendsPeriodic Trends As you go across a period the radius As you go across a period the radius

gets smaller.gets smaller. Same energy levelSame energy level More nuclear chargeMore nuclear charge Outermost electrons are closerOutermost electrons are closer

Na Mg Al Si P S Cl Ar

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OverallOverall

Atomic Number

Ato

mic

Rad

ius

(nm

)

H

Li

Ne

Ar

10

Na

K

Kr

Rb

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Electron AffinityElectron Affinity The energy change associated with adding The energy change associated with adding

an electron to a gaseous atoman electron to a gaseous atom High electron affinity gives you energy- High electron affinity gives you energy- exothermicexothermic More negative More negative Increase (more - ) from left to right Increase (more - ) from left to right

– greater nuclear charge.greater nuclear charge. Decrease as we go down a groupDecrease as we go down a group

– More shieldingMore shielding

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Ionic SizeIonic Size Cations form by losing electronsCations form by losing electrons Cations are smaller than the atom Cations are smaller than the atom

they come fromthey come from Metals form cationsMetals form cations Cations of representative elements Cations of representative elements

have noble gas configuration.have noble gas configuration.

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Ionic sizeIonic size Anions form by gaining electronsAnions form by gaining electrons Anions are bigger than the atom they Anions are bigger than the atom they

come fromcome from Nonmetals form anionsNonmetals form anions Anions of representative elements Anions of representative elements

have noble gas configuration.have noble gas configuration.

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Configuration of IonsConfiguration of Ions Ions always have noble gas Ions always have noble gas

configurationconfiguration Na is 1sNa is 1s222s2s222p2p663s3s11 Forms a 1+ ion - 1sForms a 1+ ion - 1s222s2s222p2p66 Same configuration as neonSame configuration as neon Metals form ions with the Metals form ions with the

configuration of the noble gas before configuration of the noble gas before them - they lose electronsthem - they lose electrons

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

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Group trendsGroup trends Adding energy levelAdding energy level Ions get bigger as Ions get bigger as

you go downyou go downLi+1

Na+1

K+1

Rb+1

Cs+1

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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 Energy level changes between

anions and cationsanions and cations

Li+1

Be+2

B+3

C+4

N-3O-2 F-1

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Size of Isoelectronic ionsSize of Isoelectronic ions Iso - sameIso - same Iso electronic ions have the same # Iso electronic ions have the same #

of electronsof electrons AlAl+3+3 Mg Mg+2 +2 NaNa+1 +1 Ne FNe F-1 -1 OO-2 -2 and Nand N-3-3 all have 10 electronsall have 10 electrons all have the configuration 1sall have the configuration 1s222s2s222p2p66

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Size of Isoelectronic ionsSize of Isoelectronic ions Positive ions have more protons so Positive ions have more protons so

they are smallerthey are smaller

Al+3

Mg+2

Na+1 Ne F-1 O-2 N-3

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ElectronegativityElectronegativity

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

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

How “greedy”How “greedy” Big electronegativity means it pulls Big electronegativity means it pulls

the electron toward itself.the electron toward itself. Atoms with large negative electron Atoms with large negative electron

affinity have larger electronegativity.affinity have larger electronegativity.

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Group TrendGroup Trend The further down a group more The further down a group more

shieldingshielding Less attracted (ZLess attracted (Zeffeff)) Low electronegativity.Low electronegativity.

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Periodic TrendPeriodic Trend Metals are at the left endMetals are at the left end Low ionization energy- low effective Low ionization energy- low effective

nuclear chargenuclear charge Low electronegativityLow electronegativity At the right end are the nonmetalsAt the right end are the nonmetals More negative electron affinityMore negative electron affinity High electronegativityHigh electronegativity Except noble gasesExcept noble gases

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Ionization energy, electronegativity

Electron affinity INCREASE

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Atomic size increases,

Ionic size increases

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Parts of the Periodic TableParts of the Periodic Table

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The information it hidesThe information it hides Know the special groupsKnow the special groups It is the number and type of valence It is the number and type of valence

electrons that determine an atom’s electrons that determine an atom’s chemistry.chemistry.

You can get the electron configuration You can get the electron configuration from it.from it.

Metals lose electrons have the lowest IEMetals lose electrons have the lowest IE Non metals- gain electrons most negative Non metals- gain electrons most negative

electron affinitieselectron affinities

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The Alkali MetalsThe Alkali Metals Doesn’t include hydrogen- it behaves Doesn’t include hydrogen- it behaves

as a non-metalas a non-metal decrease in IEdecrease in IE increase in radiusincrease in radius Decrease in densityDecrease in density decrease in melting pointdecrease in melting point Behave as reducing agentsBehave as reducing agents

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Reducing abilityReducing ability Lower IE< better reducing agentsLower IE< better reducing agents Cs>Rb>K>Na>LiCs>Rb>K>Na>Li works for solids, but not in aqueous works for solids, but not in aqueous

solutions.solutions. In solution Li>K>NaIn solution Li>K>Na Why?Why? It’s the water -there is an energy It’s the water -there is an energy

change associated with dissolvingchange associated with dissolving

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Hydration EnergyHydration Energy LiLi++(g) (g) → Li→ Li++(aq)(aq) is exothermic is exothermic for Lifor Li++ -510 kJ/mol -510 kJ/mol for Nafor Na+ + -402 kJ/mol-402 kJ/mol for Kfor K++ -314 kJ/mol -314 kJ/mol Li is so big because of it has a high Li is so big because of it has a high

charge density, a lot of charge on a charge density, a lot of charge on a small atom.small atom.

Li loses its electron more easily Li loses its electron more easily because of this in aqueous solutionsbecause of this in aqueous solutions

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The reaction with waterThe reaction with water Na and K react explosively with waterNa and K react explosively with water Li doesn’t.Li doesn’t. Even though the reaction of Li has a Even though the reaction of Li has a

more negative more negative H than that of Na and KH than that of Na and K Na and K meltNa and K melt H does not tell you speed of reactionH does not tell you speed of reaction More in Chapter 12.More in Chapter 12.