Diapositiva 1

Jari-jari ion (ionic radii)Perhatikan pola berikut ini :Na+ (116 pm), Mg2+ (86 pm), Al3+ (67,5 pm)Semakin besar bilangan oksidasi kation, semakin kecil ukuran jari-jarinya--- ingat lagi konsep jari2 (jarak antara inti atom dengan elektron valensi)---makin besar biloks kation (makin banyak elektron valensi yang lepas)--- makin pendek jarak antara inti atom dengan elektron valensinya, makin kecil ukuran ion, makin besar gaya tarik yang dimiliki kation.

Untuk atom-atom dengan bilangan oksidasi banyak dapat dilihat pola jari-jari ionnya sbb :Ag+ (114 pm), Ag2+ (93 pm) dan Ag3+ (81 pm)Semakin besar biloks nya (untuk bilangan koordinasi yg sama)---semakin kecil jari-jari ionnya.

Perhatikan pula berikut : untuk ion yang sama tapi denga bilangan koordinasi yg berbeda :

ionCNIon radii (pm)Ag+2814114512361297136Pada ion dengan biloks yg sama, semakin besar CN nya, semakin besar jari-jari ionnyaCoordination Number (CN): jumlah anion yg dapat berikatan dengan kation.

Jumlah anion yg dapat berikatan dengan kation akan meningkat sebagaimana peningkatan perbandingan radius jari-jari---Semakin besar CN

perbandingan radius jari-jari = r cation/r anion.

Semakin besar perbandingannya, semakin banyak pula anion yg dapat berikatan dgn kation. Radius RatioArrange of Anions around the cationCoordination Number (CN)0.15 - 0.22Corners of equilateral triangle30.22 - 0.41Corners of a tetrahedron40.41 - 0.73Corners of an octahedron60.73 1,37corners of a cube81Midpoints of cube edges12Soal :Tentukan CN maksimum K2O untuk K+ dan O2- dari : K2O (r K+ = 152 dan rO2- = 126)Jawab :

2. Tentukan CN maksimum SnO2 untuk Sn+4 dan O2- dari : SnO2 (r Sn+4 = 83 dan rO2- = 126)

Coordination Number 2

The first step is:Ag+ + Cl- AgCl (white ppt) and to ensure that the precipitate is really the chloride salt, two further tests must be done: AgCl + 2 NH3 [Ag(NH3)2]+ and [Ag(NH3)2]+ + HNO3 AgCl (re-ppts) The reaction of a bidentate ligand such as 1,2-diaminoethane with Ag(I) does not lead to chelated ring systems, but instead to linear two coordinate complexes. One reason for this is that bidentate ligands can NOT exist in trans arrangements, that is they can NOT span 180 degrees. Coordination Number 3Once again, this is not very common for first row transition metal ions. Examples with three different geometries have been identified:

Trigonal planarWell known for main group species like CO32- etc., this geometry has the four atoms in a plane with the bond angles between the ligands at 120 degrees.Trigonal pyramid More common with main group ions.

T-shapedCoordination Number 4

Two different geometries are possible. The tetrahedron is the more common while the square planar is found almost exclusively with metal ions having a d8 electronic configuration.

Tetrahedral

Square Planar

Coordination Number 5

Square pyramid

Trigonal Bipyramid

8Coordination Number 6

Hexagonal planar

Trigonal prism

Octahedral (Oh)

Coordination Number 7

Capped octahedron

Capped trigonal prism

Pentagonal Bipyramid

Contoh :Predict the coordination of NaCl and CsCl

Jawab :The radius of Cl -1 is 1.81 and the radius of Na +1 is 0.99. The radius ratio is therefore 0.99/1.81 or 0.55. This would predict that Na is in octahedral coordination with Cl.

The radius of Cs +1 is 1.67 and thus the radius ratio is 0.92 which would predict that Cs is surrounded by 8 (cubic) Cls in its structure.

Pengaruh suhu dan tekanan pada CN : Al +3 dapat berbentuk oktahedral maupun tetrahedral dengan silikat. Hal ini dikarenakan pengaruh suhu dan temperatur. Semakin tinggi temperatur (tekanan semakin rendah), menyebabakan CN menurun dan sebaliknya.