- a molecule of ion that donates a pair of electrons to a central metal ion to form a coordinate bond/dative covalent bond

24 - Transition elements Flashcards by Cherry .x

what are d-block elements?
properties

3d sub-shell has the highest energfy and electrons are added to 3d orbitals
metallic, high MP and BP, shiny, conduct electricity and heat

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how are d-block orbitals filled
how are ions formed

atoms of d-block elements fill their 4s sub shell before the 3d sub shell
- 4s sub shell is at a lower energy than 3d

-> ions formed by emptying the 4s orbital before the 3d

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what are the exceptions to the expected filling of block elements

chromium and copper

In both cases an electron is promoted from the 4s to the 3d to achieve a half full and full d-subshell, respectively

Chromium and copper have the following electron configurations, which are different to what you may expect:

Cr is [Ar] 3d5 4s1 not [Ar] 3d4 4s2
Cu is [Ar] 3d10 4s1 not [Ar] 3d9 4s2

This is because the [Ar] 3d5 4s1 and [Ar] 3d10 4s1 configurations are energetically more stable

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what are transition metals

d-block elements that form at least one ion with a partially filled d-orbital

Sc and Zn dont fit this definition
Scandium only forms the ion Sc3+, configuration [Ar] 3d0
Zinc only forms the ion Zn2+, configuration [Ar] 3d10

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General properties of TM

Variable oxidation states
Form complex ions
Form coloured compounds
Behave as catalysts

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Variable Oxidation States?

can form compounds withmore than one oxidation state
-> Iron(II) FeCl2 and Irons(III) FeCl3
-the number of oxidation states increase across the period to manganese, then decreases

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Forming coloured compounds

compounds and ions of TM are often coloured
->colour of the solution of a TM compound depends on the oxidation state

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Iron and it coloured compounds

Iron II -> pale green
Iron II -> yellow

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Chromium and its coloured compounds

Cr III -> green
Cr VI -> yellow or orange

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Transition elements as catalysts

Since transition elements can have variable oxidation states, they make excellent catalysts

During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction

Substances can also be adsorbed onto their surface and activated in the process

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give 2 examples of TM as catalysts

An example is the use of iron, Fe, in the Haber process for making ammonia
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

The decomposition of hydrogen peroxide is a common reaction in the study of chemical kinetics and uses manganese(IV) oxide as the catalyst
2H2O2 (g) → 2H2O (aq) + O2 (g)

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complex ion

is formed when one or more molecules or negatively charged ions bond to a central metal ion

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what is a ligand?

a molecule of ion that donates a pair of electrons to a central metal ion to form a coordinate bond/dative covalent bond

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what is dative/coordinate bond?

when one of the bonded atom provides both of the electrons for the bond

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what is the coordination number?

the number of coordinate bonds attached to the central metal ion

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monodentate ligands
give examples

a ligand that can donate one pair of electrons to a central metal ion
H20:
:NH3
:Cl-
:CN-
:OH-

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Bidentate ligands
give examples

can donate two lone pairs of electrons to the central metal ion - each molecule can form two coordinate bonds

1,2 - diaminoethane or en
ethanediote (oxalate) ion

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where are the lone pairs on 1,2 - diaminoethane and ethanediote (oxalate) ion

each nitrogen atom donates a pair of electrons
each negatively charged oxygen atom donates a lone pair

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shape of a complex ion with six coordinate bonds?

it gives an octahedral shape
- bond angle is 90

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shape of a complex ion with 4 coordinate bonds?

tetrahedral
-> 109.5
square planar
-> 90

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when is a complex ion tetrahedral or square planar?

square planar when there are 8 electrons d-electrons in the highest energy d-sub-shell
-Platinum II
palladium II
gold III

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what kind of stereoisomerism do complex ions show

cis-trans isomerism
optical

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when can a complex ion show cis-trans isomerism?

four coordinate square planar complexes that have no more then two identical ligands

six coordinate complex ions monodentate (four of one type of one ligand and two of of another type of ligand)

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four and six coordinate complex ions containing two different monodentate ligands

what kind of stereoisomerism does this show

cis-trans

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some six coordinate complex ions with monodentate and bidentate ligands what kind of stereoisomerism does this show

cis-trans and optical

when does a complex ion show optical isomerism

some six coordinate complex ions with monodentate and bidentate ligands

explain cis-trans isomerism in square planar complexes

- found in four coordinate square planar complexes that have no more than two identical ligands - the ligands are arranged in the same plane at the corners of a square of a square at 90 - cis isomer has two identical groups adjacent to each other 90 degrees to each other - trans isomer has two identical ligands opposite to each other (hypotenuses). 180 degrees between each other

give an example of cis-trans isomerism in a square planar complex -> draw it boyyyyyy

[Pd(NH3)2CL2]

explain cis-trans isomerism in octahedral complex with monodentate ligands

let the ligands be 4 x A and 2 x B Cis-> two B ligands aare adjacent to each other at 90 degrees Trans -> two B ligands are at 180 degrees to each other and on the same plane

give an example of cis-trans isomerism in octahedral complex with monodentate ligands draw it lazy bitch

[Co(NH3)4Cl2]+

explain cis-trans isomerism in octahedral complex with bidentate ligands

structural formula of en

NH2CH2CH2NH2

explain optical isomerism in octahedral complexes

- optical isomerism only occurs in octahedral complexes containing two or more bidentate ligands - enantiomers are non-superimposable mirror images of each other - the cis isomer of a octahedral complex with 2 x B(bidentate) can exist as two optical isomers but the trans isomer cant- it can be superimposed

colours of chromium ions

Cr2O7 2- (Cr= +6) is orange Cr3+ (Cr=+3) is green

Cr 3+ metal aqua ion

violet solution [Cr(H2O)6]3+

Fe 3+ metal aqua ion

yellow solution [Fe(H2O)6]3+

Fe 2+ metal aqua ion

pale green solution [Fe(H2O)6]2+

Mn 2+ metal aqua ion

Pale pink [Mn(H2O)6]2+

Cu 2+ metal aqua ion

pale blue [Cu(H2O)6]2+

Cr 3+ with little OH-

Grey? [Cr(OH)3(H2O)3] (s)

Cr 3+ with excess OH-

dark green solution [Cr(OH)6]3–

Cr 3+ with little NH3

green grey precipitate [Cr(OH)3(H2O)3] (s)

Cr 3+ with excess NH3

Purple solution [Cr(NH3)6]3+

Fe 3+ with little OH-

orange brown precipitate Fe(OH)3(H2O)3(s)

Fe 3+ with excess OH-

orange brown precipitate Fe(OH)3(H2O)3(s)

Fe 3+ with little NH3

Orange brown precipitate Fe(OH)3(H2O)(s)

Fe 3+ with excess NH3

orange brown precipitate Fe(OH)3(H2O)(s)

Cu 2+ with little OH-

Pale blue precipitate Cu(OH)2(H2O)4(s) OH- accept H+ from 2 water ligands

Cu 2+ with excess OH-

Pale Blue precipitate Cu(OH)2(H2O)4(s) OH- accept H+ from 2 water ligands

Cu 2+ with little NH3

Pale blue precipitate Ammonia acts as a base Cu(OH)2(H2O)4(s) + 2NH4+

Cu 2+ with excess NH3

deep blue solution [Cu(NH3)4(H2O)2]2+

Cu 2+ with NH3 not in excess

deep blue solution

Mn 2+ with little OH-

light brown precipitate Mn(OH)2(H2O)4(s)

Mn 2+ with excess OH-

light brown precipitate Mn(OH)2(H2O)4(s)

Mn 2+ with little NH3

light brown precipitate Mn(OH)2(H2O)4(s)

Mn 2+ with excess NH3

light brown precipitate Mn(OH)2(H2O)4(s)

Fe 2+ with little OH-

Dark green precipitate Fe(OH)2(H2O)(s)

Fe 2+ with excess OH-

Dqrk green precipitate Fe(OH)2(H2O)(s)

Fe 2+ with little NH3

green precipitate Fe(OH)2(H2O)(s)

Fe 2+ with excess NH3

green precipitate Fe(OH)2(H2O)(s)

Iron Redos reactions, TM

Fe2+ + [O] -> Fe3+ - can be oxidised using MnO4- in acidic conditions pale green -> orange brown

Chromium Redox reactions TM oxidation states and compoiunds

Cr3+ Cr2O72- Cr2+

Chromium Redox reactions TM reducing Cr2O7 2-

forms Cr3+ and Cr2+ using zinc in acidic conditions

Chromium Redox reactions TM oxidising Cr3+

forms Cr2O7 2- Using hydrogen peroxide in alkaline conditions - initially forms CrO4 2- but converted to Cr2O7 2- by acidification

oxidation of Cr3+ with hot alkaline H2O2

CrO4 2- yellow

Cr2O7 2-

from K2Cr2O7(s) in 0.1mol dm-3 H2SO4 orange

Copper Redox reactions TM

Cu2+ can be reduced by zinc

Cu+ to Cu and Cu2+

Disproportionation of Cu+ =brown solid (Cu) and =blue solution (CuSO4

CuCl4 2-

excess HCl to Cu2+(aq) yellow

CoCl4 2–

from CoCl2.6H2O(s) plus water and excess HCl blue