Transition Metals(1)

7/28/2019 Transition Metals(1)

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INTRODUCTIONTOTRANSITION

METALSDr F. Marais


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TRANSITIONELEMENTS

All metals

All have variable oxidation states

Great industrial value due to increased density

afforded by filling penultimate orbitals Size (volume occupied) doesnt increase much

Mass increases across d- orbital more than it would

normally moving down a period


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Properties of d-block elements

INTRODUCTION:

Transition & inner transition comprise 4 series

Sc(21) to Cu(29) 3-d block

Y(39) to Ag(47) 4-d block

La(57) to Au(79) 4-f and 5-d block

Ac(89) to Lr(103)(lawrencium)

5-f and 6-d block


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COMPLEX FORMATION

s- and p- block elements

form only a few complexes.

Transition elements have small

highly charged ions

vacant low energy orbitals

accept lone pairs of electrons

form many complexes


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Penultimate shell is expanding

Many common properties

All metallic

Elements usually exist in more than one

oxidation state


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OXIDATIONSTATESANDORDEROFFILLING

OFD-BLOCKFOR 1STSERIES

Sc Ti V Cr Mn Fe Co Ni Cu Zn

electronic

structure

d1s2 d2s2 d3s2 d4s2

d5s1

d5s2 d6s2 d7s2 d8s2 d9s2

d10s1

d10s2

oxidation

states II

III

II

III

IV

II

III

IV

V

I

II

III

IV

V

VI

II

III

IV

V

VI

VII

II

III

IV

V

VI

II

III

IV

V

II

III

IV

I

II

III

II


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Reactivity decreases

With each following series

From L to R across any series

*Pt, Au (& others in same groups)

resist forming compounds with oxygen- referred to as noble metals.


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The most stable states in the 1st

series

when the d-shell is empty

when it is half full

when it is completely full


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PROPERTIES OF TRANSITION

ELEMENTS

METALLIC PROPERTIES

Metals are dense and have highmelting and boiling points. Since the

electrons fill an inner orbital (from L to

R) the atomic radius does not increase

much so only density will increase

across each series.


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COLOURED IONS

The d-orbital comprises 5 degeneratesub-orbitals which can each hold 2 electrons.

Transitions of d-electrons is in the visibleenergy region.

The colour of a particular transition metalion depends upon:

* The nature of ligands it is surrounded by

* An incomplete d-level


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Movement, or rearrangement, of electrons

Within the 5 degenerate sets requires energy

which is observed as visible colour.

In addition, when electrons exist in degenerate sets

The energy difference between the sets

results in emission of energy.

The degree of splitting between the levels depends

on the type of ligand surrounding the metal ion.

The different energy differences are observed

as different wavelengths and for d-electrons,

different colours within the visible spectrum.


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CATALYTIC ACTIVITY

Transition metal ions function as catalysts

by changing their oxidation states.

Catalysis at a solid surface involves

formation of bonds between catalyst atomsand surface molecules.

In the transition elements both s-

and d- electrons are availableThis increases bonding possibilities

lowers activation energy

makes desired reaction more favourable.


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PARAMAGNETISM

Most substances are weakly repelled by a

strong magnetic field

= diamagnetic

Some are weakly attracted by it

= paramagnetic

A large force of attraction is referred to as

ferromagnetism.


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Electrons spin on their axes within

orbitals.

A full orbital containing 2 electrons with

opposite spin, (Hunds Rule) will have a

zero magnetic moment.

Increased levels of Para magnetism

indicates maximum single occupationof orbitals.

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Transition Metals(1)