lectures 7-8 - University of California, Santa Cruz 7-8 15 covalent and metallic atomic radii periodic trends (fig. 12.38) larger Z smaller r larger n larger r but : metallic/covalent

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Chemistry 1B Fall 2012Lectures 7-8

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Chemistry 1B

Fall 2012

lectures 7-8(pp. 571-580,604-607)

[pp. 571-582, 606-609]7th

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periodicity (figure 12.29)

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bad joke

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atomic radii (10-12 m):

Li 152Na 186K 227Rb 247Cs 265Fr 270

butLi 152

EXPLAIN THIS !!!! (atomic radii, fig. 12.38)

Be 113 B 88 C 77 N 70 O 66 F 64 Ne 69*

increase mass of atom

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explain this

Na (s) + ½Br2 () → Na+Br (s)

why Na+ ?

why Br ?

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periodic properties of atoms and their ions

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2eff18

eff

n

ZJ102.18E

Z n, with electron of energy phase gas

210

eff

2

eff

12

"Bohr" radius in gas phase

nr (0.529 10 m)

Z

nr (52.9 pm)

Z

pm=10 m (picometer)

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basic trends for n and Zeff in periodic table (figure 8.9, Silberberg)

Zeff increases across row (period)nin

crea

ses

dow

n co

lum

n (g

roup

) n is not changing

Zef

fis

‘rel

ativ

ely’

con

stan

t

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Estimating atomic radii (metallic and covalent) (figs. Zumdahl 12.37, Silberberg 8.14)

for metals

for nonmetals-can vary from compound to compound

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covalent and metallic atomic radii periodic trends (fig. 12.38)

rsmaller Zlarger

rlarger nlarger

:but

radiiovalent metallic/c

for literally'' too formula taket don'

Znm)10(0.529r

radiusBohr''phasegas

eff

eff

210

Zeffn

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atomic radii (Silberberg fig. 8.15) numerical values differ slightly from Zumdahl

rsmaller Zlarger

rlarger nlarger

:but

radiiovalent metallic/c

for literally'' too formula taket don'

Znm)10(0.529r

radiusBohr''phasegas

eff

eff

210

Zeffn

transition metals( special considerations)

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how would the radius of F compare to that of F ?• F 1s22s22p5 F 1s22s22p6

• outer electron n=2 for both

• how does Zeff for 2p in F compare to Zeff for 2p in F ?

o 2p e in F is shielded by electrons in same subshell

o 2p e in F is shielded by electrons in same subshell

o (Zeff)F (Zeff) F

• radius (F) radius (F )

• Experiment: F: r=64 pm F : r=136 pm(fig. 12.38) (fig. 13.8)

radii of ions (F vs F ) r ≈ 52.9 n2/Zeff pm

4

5>

<

?

??

?

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more examples of comparing radii

• Na vs Na+

• Ne vs Na+

(note experimental data for Na+ , fig. 13.8and Ne, fig. 12.38 not comparable see)

• O2 vs F

• O2 vs F

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ionization energies (IE’s)

energy required to remove an electron from a gaseous atom (ion)

X (g) + (energy=IE) →X(g)+ + e-

as in chapter 9:

energy positive (+) when absorbed in reaction (endothermic)

energy negative () when released in reaction (exothermic)

IE’s generally positive

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ionization energies ( Zumdahl fig. 12.35, Silberberg, fig. 8.18)

why? Ga Ca Al,Mg B, Be

why? Se AsS,P O, N

exceptions

2

2eff18

eff

n

ZJ102.18E

Z n, with

electronofenergyphasegas

IElarger Zlarger

IEsmaller nlarger

EIE

eff

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successive gas phase ionization energies in kJ/mol (p571; S9)

Al ([He]2s22p63s23p1) → Al+ ([He]2s22p63s2) + e IE1=

Al+ ([He]2s22p63s2) → Al2+ ([He]2s22p63s1) + e IE2=

Al2+ ([He]2s22p63s1) → Al3+ ([He]2s22p6) + e IE3=

Al3+ ([He]2s22p6) → Al4+ ([He]2s22p5) + e IE4=

580

1815

2740

11,600

• successive IE’s get larger (positively charged ions have greater Zeff )

• large jumps in IE when n of electron removed changes

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electron affinities (EAs, pp 576-577)

the energy of the reaction when an electron is added to an atom

X(g) + e → X (g) + (energy = EA)

negative EA means energy given off (exothermic)

positive EA means ion unstable relative to neutral atom

(some older texts use opposite)

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electron affinities (Zumdahl fig 12.36; Silb fig. 8.20)

Zeffn higher n smaller (less negative) EA

larger Zeff larger (more negative) EA

positive EA negative ion unstable

[harder to measure and “less regular “ tha I.E.’s]

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F vs Cl electron affinities (Zumdahl p 577)

Zeffn higher n smaller (less negative) EA

small size of F

HW #2Prob 26a (12a)

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Journal of Fluorine Chemistry 2002

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summary (Silb, fig. 8.21)

Zeffn

2

2eff18

eff

n

ZJ102.18E

Z n, with electron of energy phase gas

210

eff

gas phase 'Bohr' radius

nr (0.529 10 m)

Z

EAs get more negative

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Zumdahl (section 12.16, figure 12.39)

not responsible forpp. 580-582

BUT

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reactivity and periodic structure (Silberberg figure 8.22)

metallic vs non-metallic behavior• IE and EA

• melting point and conductivity

• acid-base behavior of oxides (not responsible 1B before 1A)

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periodic table of comic books

http://www.uky.edu/Projects/Chemcomics/

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END OF LECTURES 7-8

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comparing Na+ to Ne (similar experimental measures)

Zum fig 12.38

Zum ~ fig 13.8Na+ 95 pm

Neall 10-electron atoms/ionsisoelectronic configurations

Z (and Zeff) decrease ï larger radius

Z (and Zeff) increase ï smaller radius

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figure Silberberg 9.1

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Silberberg figure 8.23

metal non-metal

melting point, conductivity decrease

mel

ting

poin

t, c

ondu

ctiv

ity d

ecre

ase

non-metal

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radii for transition metal (neutral) atoms in 4th period

Even though the E4s < E3d

(due to penetration effects),the average position (radius)of the 3d oribtals is somewhatsmaller.

Thus, in terms of atomic size, the 4s is the “outermost” orbital for all of the atoms; and as one goes across the period, successive e’s are added to “inner” 3d orbitals and the radii are relatively constant.

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• metal oxides dissolve in water to give basic solutions

K2O (s) + H2O () → 2 KOH (aq) → 2K+ (aq) + 2 OH− (aq)

BaO(s) + H2O () → Ba(OH)2 (aq)→ Ba2+ (aq) + 2 OH− (aq)

• non-metal oxides dissolve in water to give acidic solutions

N2O5(s) + H2O () → 2 HNO3 (aq) → 2H+ (aq) + 2 NO3− (aq)

SO3 (g) + H2O () → H2SO4 (aq) → H+ (aq) + HSO4− (aq)

acid-base properties of metallic and nonmetallic oxides

basic

acidic

(2012 not responsible; Chem 1B before Chem 1A)

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lectures 7-8 - University of California, Santa Cruz 7-8 15 covalent and metallic atomic radii periodic trends (fig. 12.38) larger Z smaller r larger n larger r but : metallic/covalent