Inorganic at University College London, University Of London | Flashcards & Summaries

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TESTE DEIN WISSEN
What factors affect ionic radius?
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TESTE DEIN WISSEN
-number of electron shells: ionic radius increases down a group for this reason
- oxidation state:   ionic radius decreases with oxidation state
- coordination number: ionic radius increases as  coordination number increases

Lösung ausblenden
TESTE DEIN WISSEN
What are the general equations for radius ratio? ( anion and cation )
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TESTE DEIN WISSEN
r- = anion radius
r+ = cation radius
If r - >r + : ratio = r+/r- 
If r+>r- : ratio =r-/r+
Radius radius is always less than 1

Lösung ausblenden
TESTE DEIN WISSEN
How does a  cation’s size affect it’s coordination number?

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TESTE DEIN WISSEN
As cation size increases it becomes easier to fit more anions around a given cation
If coordination number is 4 it indicates that there is a large mismatch between anion and cation size.
If a cation and anion are roughly the same size coordination number is 8
In between being very similar  and very different in size ( between an anion and cation) coordination number is 6
Lösung ausblenden
TESTE DEIN WISSEN
What criticisms are there of the radius  ratio model?
Lösung anzeigen
TESTE DEIN WISSEN
- Using a standard value for ionic radius gives errors '
- radius ratio only gives the correct structure about 50% of the time 
- materials are rarely 100% ionic, covalency implies directional bonding
Lösung ausblenden
TESTE DEIN WISSEN
What are the approximate radius ratio values for:
a) tetrahedral structure ( coordination number = 4)
b ) octahedral ( coordination number =6)
C) cuboidal (coordination number =8)

Lösung anzeigen
TESTE DEIN WISSEN
a) 0.225 - < 0.414
b) 0.414- < 0. 732
C)0.732 - < 1
Lösung ausblenden
TESTE DEIN WISSEN
What are the 6 parameters that any unit cell can be defined by?
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TESTE DEIN WISSEN
a, b, c, α, β, γ
Lösung ausblenden
TESTE DEIN WISSEN
 watch the video on packing and holes ( voids)
Lösung anzeigen
TESTE DEIN WISSEN
https://www.youtube.com/watch?v=B1JzFAD1GAo
search packing solids on YouTube 
Lösung ausblenden
TESTE DEIN WISSEN
What happens as coordination number increases?
Lösung anzeigen
TESTE DEIN WISSEN
Packing efficiency increases 
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TESTE DEIN WISSEN
What is lattice energy ?
Lösung anzeigen
TESTE DEIN WISSEN

the energy change when one mole of
gaseous ions, which are infinitely separated, form a crystal at 0K
Lattice energy is ΔU at 0K
Lösung ausblenden
TESTE DEIN WISSEN
ΔHlatt is…
Lösung anzeigen
TESTE DEIN WISSEN
Always an exothermic process and so the energy change is negative
Lösung ausblenden
TESTE DEIN WISSEN
What determines r0?
Lösung anzeigen
TESTE DEIN WISSEN
1.Attractive forces between unlike charges, long ranged interaction
2.At close range, Pauli repulsion, electrons of one ion are pushed close to electrons of neighbouring ions. 
Lösung ausblenden
TESTE DEIN WISSEN
Define coulomb attraction
Lösung anzeigen
TESTE DEIN WISSEN
The energy change upon bringing two ions from infinite separation to a separation of r
Lösung ausblenden
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Q:
What factors affect ionic radius?
A:
-number of electron shells: ionic radius increases down a group for this reason
- oxidation state:   ionic radius decreases with oxidation state
- coordination number: ionic radius increases as  coordination number increases

Q:
What are the general equations for radius ratio? ( anion and cation )
A:
r- = anion radius
r+ = cation radius
If r - >r + : ratio = r+/r- 
If r+>r- : ratio =r-/r+
Radius radius is always less than 1

Q:
How does a  cation’s size affect it’s coordination number?

A:
As cation size increases it becomes easier to fit more anions around a given cation
If coordination number is 4 it indicates that there is a large mismatch between anion and cation size.
If a cation and anion are roughly the same size coordination number is 8
In between being very similar  and very different in size ( between an anion and cation) coordination number is 6
Q:
What criticisms are there of the radius  ratio model?
A:
- Using a standard value for ionic radius gives errors '
- radius ratio only gives the correct structure about 50% of the time 
- materials are rarely 100% ionic, covalency implies directional bonding
Q:
What are the approximate radius ratio values for:
a) tetrahedral structure ( coordination number = 4)
b ) octahedral ( coordination number =6)
C) cuboidal (coordination number =8)

A:
a) 0.225 - < 0.414
b) 0.414- < 0. 732
C)0.732 - < 1
Mehr Karteikarten anzeigen
Q:
What are the 6 parameters that any unit cell can be defined by?
A:
a, b, c, α, β, γ
Q:
 watch the video on packing and holes ( voids)
A:
https://www.youtube.com/watch?v=B1JzFAD1GAo
search packing solids on YouTube 
Q:
What happens as coordination number increases?
A:
Packing efficiency increases 
Q:
What is lattice energy ?
A:

the energy change when one mole of
gaseous ions, which are infinitely separated, form a crystal at 0K
Lattice energy is ΔU at 0K
Q:
ΔHlatt is…
A:
Always an exothermic process and so the energy change is negative
Q:
What determines r0?
A:
1.Attractive forces between unlike charges, long ranged interaction
2.At close range, Pauli repulsion, electrons of one ion are pushed close to electrons of neighbouring ions. 
Q:
Define coulomb attraction
A:
The energy change upon bringing two ions from infinite separation to a separation of r
inorganic

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