Atomaire bindingen

- ionische binding- covalente binding- metallische binding

Ionic bonding 1

E

0E

1s

2s

2p

2 1Li :1 2s s

1s

2s

2p

2 2 5F :1 2 2s s p

between a Li atom and a F atom

Ionic bonding 2

E

0E

1s

2s

2p

2 0+Li :1 2s s

1s

2s2p

2 2 6-F :1 2 2s s p

gives Li+ F- molecule

IonizationPotential

(IP)

Electron Affinity (EA)

Energy cost: E = IP(Li) – EA(F)

Ionic bonding 3

( )U r E

Ionic binding curve:

electrontransfer

2

0

1

4

e

r

Coulombattraction

ions

( )repU r

Paulirepulsion

Binding curve has stable minimum !!

Ionic bonding 4

only works between very dissimilar atoms !!

Ionic bonding in solids

NaCl structure CsCl structure

Na+

Cl- Cl-

Cs+

common salts have ionic bonding

structure determined by relative size ions

Covalent bonding 1

Model system: one electron in two wells

wells far apart wells close

ES < EA

electron wants to pull wells close !!

( )V x

Covalent bonding 2

H2 molecule: two electrons in two wells

E1E 1E

SE

AE

H atom H atomH2 molecule

allowed by Pauli

Covalent bonding 3

He2 molecule? four electrons

E1E 1E

SE

AE

He atom He atomHe2 molecule

no electronic bonding in He2

no stable He2 molecule !!

because of Pauli exclusion principle

Hetero-atomic covalent bonding

E

1s

1s

2s

2p

H F molecule

SE

AE

S

+ -H F polar bond !!

H atom F atom

Poly-atomic covalent bonding 1

H2O molecule

22

1s

1s

covalent bonding gives directional bonds !!

Poly-atomic covalent bonding 2

CH4 molecule: tetraeder

1s

1s

1s

1s

C hybrid orbital

Covalent bonding in solids

C, Si, ... have covalent bonding

diamond structure

and compound semiconductors: GaAs, ...

Metallic bonding in solids 1

positive ions

metal: one electron in many wells

( )V x

x

( )S x

x

has a wave-like character (delocalized) ( )S x

'Fermiology'

Twee verschillende metalen met elkaar in contact contact-potentiaal

Volgende (laatste) hoor-college:

Quantum theorie van electrische geleidingIsolatoren vs. (half)geleiders, supergeleiders

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