first row transition metals

8/2/2019 First Row Transition Metals

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A Transition element is an element that forms

one or more stable ions with a partially filled dsub-shell.


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Vanadium has potentially five (5) different oxidation states as

it outer electron configuration is 4s2 3d3.

Vanadium can be reduced from the +5 states right down to the

+2 state by shaking a solution containing a compound ofvanadium (v) with zinc and dilute acid.

How solution of Vanadium can be made?

By dissolving ammonium vanadate (V), NH4VO3 in dilutesodium hydroxide solution and then adding excess dilute

sulfuric acid. The mixture contains yellow dioxovanadium(V)

ions VO+2,formed by a reaction of VO-3ions with H

+ ions.


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The equation for this reaction:

VO-3(aq) + 2H+ VO+2(aq) + H2O(l)

{yellow solution oxidation states +5}

When the yellow solution (dioxovanadium(V) solution) is

shaken with granulated zinc, it changes gradually through

green to blue oxovanadium (IV)ions,VO2+(aq)

It then changes to green vanadium (III) ions, V3+ (aq) and

finally to violet vanadium (II)ions,V2+(aq).


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Equation for BLUE solution, oxidation state +4

VO

+

2 + 2H

+

+ e

-

V

2+

+ H2O

Equation for GREEN solution, oxidation state +3

VO2+ + 2H+ + e- V3+ + H2O

Equation for VIOLET solution, oxidation state +2

V3+ + e- V2+


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Using zinc as the reducing agent

Let's look at the first stage of the reduction - from VO2+

to VO 2+ .

When zinc is added to a solution of VO2+

ions, thefollowing half reactions are involved:


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The overall cell reaction is:

Once the VO2+ ions are formed it can be reducedfurther to V3+ ions

VO2++ 2H+ + e- V3++H 2O E0 =+0.34V

Zn(s) Zn2+

(aq) + 2e-

E0=+0.76V The overall cell reaction is

2VO2++ 4H+ + Zn(S) 2V3++2H2O +Zn

2+(aq)Blue Green


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Once the V3+ ions are formed it can yet be reduced

further to V2+ ions

V3+ +e- V2+ E0= -0.26V

Zn(s) Zn2+(aq) + 2e

-

E0=+0.76V

The overall cell reaction is

2V3+ +Zn(s) 2V2+ +Zn2+(aq)green violet

E0cell =-0.26V +0.76

=+0.50V

Since the cell potential for each is positive, zinc is able

to gradually reduce vanadium from the +5 oxidation

state to the +2 oxidation state.


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Melting PointTransition metals have generally high melting points(more than 1500oC ) dueto their strong metallic bonding. Metallic bonding is defined by delocalizationof valence electrons, leaving the metal cations to be embedded in a sea ofdelocalized electrons. More delocalized electrons, the stronger the metallic

bonds. As seen in transition metals, not only some 3d electrons are delocalized,but also the 4s electrons. Compared to calcium which only has the 2s electronsto be delocalized.

DensityThe densities of the transition elements are generally higher,(except forscandium), than the densities of the s block metals which are generally low;

especially group1

Densities of individual atoms increase markedly across a period because theatomic radii decrease while the atomic masses increase. Bulk densities increase

similarly for the same packing arrangements.


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The difference in densities between transition metals and Group1 metals is

accentuated by the fact that most transition metals have close-packed structures

while Group 1metals do not (i.e. a large number of atoms closely packed in a

small space .: high densities and hard materials).

Atoms of most of the transition metals have small radii and pack in closest-packed structures with a coordination number of 12.They are .: relatively dense

compared with the metals of Group I and Group II whose larger atoms pack in

body-centered structures with a coordination number of 8.

Atomic RadiusAcross the period, the number of shielding shells remains the same, but

positive charge of nucleus increase, leading to a stronger force of attraction

between the nucleus and the valence electrons, resulting in a smaller atomic

radius. Compare calcium with iron, they have same shielding shells, but iron

has a stronger force of attraction of the valence electrons due to a greater

amount of positive charged proton. Therefore, atomic radius is smaller for the

iron. Generally, transition metals have a smaller atomic radii compared to

calcium.


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Ionic RadiusDown the group, extra layers of electrons are added leading to ions getting

bigger. Across a period, radii of ions decrease until we reach the negatively

charged ions. Radii decrease due to the face that across the period there is more

proton, and when there is a lost of electrons, there will be a stronger

electrostatic attraction between the nucleus and the outermost shell. Comparing

Ca2+ with Fe2+, in this case the degree of ionization is the same so the two can

be contrasted. Ca2+ has an ionic radius of 114 pm while Fe2+ has an ionic

radius of 77 pm. Generally, transition metals have a smaller ionic radius as

compared to calcium.

First Ionization energyAcross a period, the first ionization energy increase with increasing atomic

number as the positive charge of nucleus increase, forces of attraction between

the nucleus and valence electron strengthen, and so more energy is required to

give out that electron. It is shown in the table below that, calcium has a lowerfirst ionization energy compared to the first row transition metal and most of

the transition metals except Hafnium and Tantalum.


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ConductivityThe delocalized electrons of metals serve as mobile charge carriers for the

conduction of electricity. Compared to calcium which only has its 4s

electrons as mobile charge carriers, transition metals also have the 3delectrons as mobile charge carriers.

first row transition metals

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