Transition Metals Flashcards
Characteristics of transition metals?
Why do these occur?
-complex formation
-catalytic activity
-formation of coloured ions
-variable oxidation states
-occur due to incomplete d subshell in the atom/ion
Define transition metals
elements with an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell
Why is zinc not a transition metal
can only form 2+ ion, which has a complete d subshell
Define complex
a central metal ion surrounded by ligands
Define ligand
An atom, ion or molecule which can donate a lone electron pair.
Define coordination number
number of co-ordinate bonds formed to a central metal ion.
electron configuration of chromium
[Ar] 3d5 4s1
not [Ar] 3d4 4s2
electron configuration of copper
[Ar] 3d10 4s1 not [Ar] 3d9 4s2
What are monodentate ligands?
Give examples
-ligands that can only form one dative bond to the central metal ion
e.g.
-water (H2O) molecules
-ammonia (NH3) molecules
-chloride (Cl–) ions
-cyanide (CN–) ions
What are bidentate ligands?
Give examples
-ligands that can each form two dative bonds to the central metal ion
-due to each ligand having two atoms with lone pairs of electrons
e.g.
-1,2-diaminoethane (H2NCH2CH2NH2)
-also written as ‘en’
-ethanedioate ion (C2O42-)
-also written as ‘ox’
What are multidentate ligands?
Give examples
-ligands with more than two atoms with lone pairs of electrons
-so can form more than two dative bonds
e.g.
-EDTA4- (hexadentate ligand as it forms 6 dative covalent bonds to the central metal ion)
Complexes with water & ammonia molecules
- neutral ligands
-contain a lone pair of electrons which can be used to form a dative covalent bond with the central metal ion
In water, this is the lone pair on the oxygen atom
In ammonia
-lone pair on the nitrogen atom
-since water and ammonia are small ligands, 6 of them can usually fit around a central metal ion, each donating a lone pair of electrons, forming 6 dative bonds
-since there are 6 dative bonds, the coordination number for the complex is 6
The overall charge of a complex is the sum of the charge on the central metal ion, and the charges on each of the ligands
A complex with cobalt(II) or chromium(II) as a central metal ion, and water or ammonia molecules as ligands, will have an overall charge of 2+
The central metal ion has a 2+ charge and the ligands are neutral
Complexes with hydroxide & chloride ions
Hydroxide and chloride ions are examples of negatively charged ligands
Both ligands contain a lone pair of electrons which can be used to form a dative covalent bond with the central metal ion
Hydroxide ligands are small, so 6 of them can fit around a central metal ion and the complex formed will have a coordination number of 6
Chloride ligands are large ligands, so only 4 of them will fit around a central metal ion
Complexes with 4 chloride ligands will have a coordination number of 4
A complex with cobalt(II) or copper(II) as a central metal ion and chloride ions as ligands, will have an overall charge of 2-
The central metal ion has a charge of 2+
Each chloride ligand has a charge of 1-
There are 4 chloride ligands in the complex, so the overall negative charge is 4-
The overall positive charge is 2+
Therefore, the overall charge of the complex is 2-
A complex with chromium(III) as a central metal ion and hydroxide ions as ligands, will have an overall charge of 3-
The central metal ion has a charge of 3+
Each hydroxide ligand has a charge of 1-
There are 6 hydroxide ligands in the complex, so the overall negative charge is 6-
The overall positive charge is 3+
Therefore, the overall charge on the complex is -3
when do complexes have a linear shape
-central metal atoms or ions with two coordinate bonds
-bond angle =180o
-most common examples are a copper (I) ion, (Cu+), or a silver (I) ion, (Ag+), as the central metal ion with two coordinate bonds formed to two ammonia ligands
The second example is the diamminesilver(I) ion, [Ag(NH₃)₂]⁺, which is present in Tollens’ reagent
Tollens’ reagent is used to test for the aldehyde functional group in organic molecules
In the test, the silver(I) ion is reduced to silver atoms that produce a characteristic silver mirror on the test tube walls
when do comlexes have a tetrahedral shape
When there are four coordinate bonds the complexes often have a tetrahedral shape
Complexes with four chloride ions most commonly adopt this geometry
Chloride ligands are large, so only four will fit around the central metal ion
The bond angles in tetrahedral complexes are 109.5o