What’s coming up???• Oct 25 The atmosphere, part 1 Ch. 8• Oct 27 Midterm … No lecture• Oct 29 The atmosphere, part 2 Ch. 8• Nov 1 Light, blackbodies, Bohr Ch. 9• Nov 3,5 Postulates of QM, p-in-a-box Ch. 9• Nov 8,10Hydrogen and multi – e atoms Ch. 9• Nov 12 Multi-electron atoms Ch.9,10• Nov 15 Periodic properties Ch. 10• Nov 17 Periodic properties Ch. 10• Nov 19,22 Valence-bond; Lewis structures Ch. 11• Nov 24 Hybrid orbitals; VSEPR Ch. 11, 12• Nov 26 VSEPR Ch. 12• Nov 29 MO theory Ch. 12• Dec 1 MO theory Ch. 12• Dec 2 Review for exam

SCREENING AND PENETRATION

PENETRATION Is to get close to the nucleus

SCREENING Is to block the view of other electrons of the nucleus

LOOK AT RADIAL PROBABILITY DISTRIBUTIONS

0

0.05

0.1

0.15

0.2

0.25

0 5 10 15 20 25 30

In a multi-electron atom Zeff(s) > Zeff(p) > Zeff(d)

E4s < E3d ENERGY LEVELS REVERSE!! E A

Z

nneff 2

2

S-orbital penetrates closer to nucleus

Closer proximity to nucleus Higher effective nuclear charge, Zeff

E AZ

nneff 2

2

1s

E

2s2p

3s

3p

3d4s

4p5s

4d

The result is that 4s lies below 3d

Atoms, molecules or ions with all electrons

paired are diamagnetic.

Diamagnetic materials are weakly repelled by

magnetic fields

MAGNETIC PROPERTIES

Example:

1s 2s 2p

Ne 1s22s22p6

NEON

ALL ELECTRONS PAIRED

Spin quantum number

Electrons are influenced by a magnetic field as though they were spinning charges.They are not really, but we think of them as having “spin up” or “spin down” levels.

Atoms, molecules or ions with at least one

unpaired electron are paramagnetic.

Paramagnetic materials are strongly attracted

to magnetic fields.

MAGNETIC PROPERTIES

1s 2s 2pN 1s22s22p3

Nitrogen atom is PARAMAGNETIC

• Which of these is paramagnetic?– Na Ca

– K+ O2

PERIODIC TRENDS

We will look at some trends in experimentally determined properties such as:

IONIZATION ENERGIES

ELECTRON AFFINITIES

ATOMIC RADII

IONIC RADII

TRENDS IN ATOMIC RADIIFOR GROUPS 1,2 and 13 to 18

Orbitals bigger as n increases

Radial probability density extends further.

AT

OM

IC R

AD

IUS

AT

OM

IC R

AD

IUS

Atomic radii increase down the group

TRENDS IN ATOMIC RADIIFOR GROUPS 1,2 and 13 to 18

ATOMIC RADIUS

AT

OM

IC R

AD

IUS

AT

OM

IC R

AD

IUS

Atomic radii decrease across a period

SCREENING AND PENETRATION

ATOMIC RADIUS DECREASES ACROSS PERIOD!

WHY? AS WE ADD ELECTRONS

The electrons go into same shell and do not screen the nucleus from each other

As nuclear charge goes up, so does Zeff

Therefore radial probability pulled in….

0

0.02

0.04

0.06

0.08

0.1

0.12

0 5 10 15 20 25 30

E AZ

nneff 2

2

Zeff increases .. no screening .. radius decreases

1

2 13 14 15 16 17

18

1

2

3

4

5

6

7

1s 1s

2s

3s

4s

5s

6s

7s

2p

3p

4p

5p

6p

6d

3d

4d

5d

4f

5f

La

Ac

Zeff INCREASES

RADIUS DECREASES

DOWN GROUP...

1

2 13 14 15 16 17

18

1

2

3

4

5

6

7

1s 1s

2s

3s

4s

5s

6s

7s

2p

3p

4p

5p

6p

6d

3d

4d

5d

4f

5f

La

Ac

Zeff D

EC

RE

AS

ES

RA

DIU

S IN

CR

EA

SE

S

FOR GROUPS 1,2 and 13 to 18

TRENDS IN IONIC RADII

Same reasons as for atomic radii…….

Cations and anions…...

IONIC RADIUS

ION

IC R

AD

IUS

ION

IC R

AD

IUS

Cations are smaller than their corresponding

neutral atoms.

Anions are larger than their corresponding neutral atoms.

Na is 186 pm and Na+ is 95 pm

F is 64 pm and F- is 133 pm

same nuclear charge and repulsion among electrons increases radius

One less electron electrons pulled in by nuclear charge

O < O– < O2–

QUESTIONS…...

ISOELECTRONIC SPECIES?

EXAMPLES

Which is bigger?

Na or Rb Rb …. higher n, bigger orbitals

K or Ca K …. poorer screening for Ca

Ca or Ca2+ Ca …. bigger than cation

Br or Br- Br …. smaller than anion

What about

QUESTIONThe species F-, Na+,Mg2+ have relative sizes in which order?

1 F-< Na+<Mg2+

2 F-> Na+>Mg2+

3 Na+>Mg2+> F-

4 Na+=Mg2+= F-

5 Mg2+> Na+>F-

ALL 1s22s22p6

ALL are isoelectronic

QUESTIONThe species F-, Na+,Mg2+ have relative sizes in which order ?

1 F-< Na+<Mg2+

2 F-> Na+>Mg2+

3 Na+>Mg2+> F-

4 Na+=Mg2+= F-

5 Mg2+> Na+>F-

Check numbers

Na+ is 95 pm

Mg2+ is 66 pm

F- is 133 pm

ELECTRON AFFINITY

the energy change associated with the addition

of an electron to a gaseous atom.

X + e– X–

In general no clear cut trends…….

F(g) + e– F–(g) E= -328 kJmol-1

EA = E the electron affinity is negative if E<0.

TWO DEFINITIONS!

the electron affinity is positive if E<0.EA = -E

TRENDS IN EA

ELECTRON AFFINITYMORE NEGATIVE

EL

EC

TR

ON

AF

FIN

ITY

MO

RE

NE

GA

TIV

E

EL

EC

TR

ON

AF

FIN

ITY

MO

RE

NE

GA

TIV

E

-200

-100

0

100

200

300

400

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

ATOMIC NUMBER

-ELE

CT

RO

N A

FF

INIT

Y

H

He

Li

Be

B

C

N

O

F

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

ELECTRON AFFINITIES

What is special about … He, Ne and Ar?Be, N and Mg?

• He, Ne, Ar: rare gases … adding electron to filled shell … must increase n

• Be, Mg: alkali earths … adding electron to filled sub-shell … must increase l

• N: Hund’s rule stability… adding electron to ½-filled degenerate p-shell

• Q: what would you predict for… Cr, Fe?

TRENDS IN IONIZATION ENERGIES

The ionization energy of gaseous atoms

M(g) M+(g) + e-

of the elements have been measured….

And we find…….

TRENDS IN FIRST IE

Electrons closer to nucleus more tightly held

Zeff D

EC

RE

AS

ES

Zeff INCREASES UP THE GROUP ION

IZA

TIO

N E

NE

RG

Y

ION

IZA

TIO

N E

NE

RG

YFirst Ionization

energies decrease down the group

TRENDS IN FIRST IE

Greater effective nuclear charge across period

Poor shielding by electrons added

Zeff INCREASESI E A

Z

neff. . 2

2

IONIZATION ENERGY

ION

IZA

TIO

N E

NE

RG

Y

TRENDS IN FIRST IE

0

500

1000

1500

2000

2500

0 1 2 3 4 5 6 7 8 9

GROUP NUMBER

ION

IZA

TIO

N E

NE

RG

Y(k

J/m

ol)

1 2 13 14 15 16 17 18

n=1

n=2

n=3

n=4

The noble gases have the highest ionization energy!Closed shells most stable