TRANSITION METALS ~ SCC Education

TRANSITION METALS

Illustrated by the elements: Cr, Mn, Fe and Cu.

Summary

· The d block elements in the fourth period contain the traditional metals - there are 10

· all metallically bond, and are often hexagonally close packed. They form alloys eg steel, brass and bronze. These are of variable composition; and can be made to alter both physical (strength, malleability) and chemical properties (chemical reactivity, catalytic effect)

· Have high melting points and boiling points, and are very strong and dense. This is because their metallic bonds are strong, with a large number of delocalised electrons (4s + some 3d) and radii are small

· Radii are very similar and relatively small. This is because the nuclear charge is high and the 3 d electrons are diffuse and do not screen the valence electrons from this large charge.

· they are not very reactive because their ionisation energies are high compared to Groups I and II, this high IE again arises because of the large nuclear charge and small radii

· They form compounds with ionic and covalent character and with variable oxidation states; The small highly charged cations have a string polarising power and even simple compounds like chlorides and bromides have a very large % covalency in nominally ionic bonds.

· They form complexes, which are often coloured, with a huge variety of ligands. The bonding is dative covalent, but usually called co-ordinate bonding, in transition metal complexes..

· They are of major importance as industrial catalysts and play a part in biological enzymes

The electron configurations are shown in Table 1

Table 1

Element	Atomic number	Element Electron configuration	Common 2+	oxidation states -compounds other
Scandium	21	1s²2s²2p⁶3s²3p⁶3d¹4s²	₁₈Ar3d¹	3+: ₁₈Ar
Titanium	22	1s²2s²2p⁶3s²3p⁶3d²4s²	₁₈Ar3d²	4+ ₁₈Ar
Vanadium	23	1s²2s²2p⁶3s²3p⁶3d³4s²		3+, 4+ and 5+
Chromium	24	1s²2s²2p⁶3s²3p⁶3d⁵4s¹^*	₁₈Ar3d⁴	3+ ₁₈Ar3d³; VI 3d⁰
Managanese	25	1s²2s²2p⁶3s²3p⁶3d⁵4s²	₁₈Ar3d⁵	VII 3d⁰- most stable
Iron	26	1s²2s²2p⁶3s²3p⁶3d⁶4s²	₁₈Ar3d⁶	3+ ₁₈Ar3d⁵- most stable
Cobalt	27	1s²2s²2p⁶3s²3p⁶3d⁷4s²
Nickel	28	1s²2s²2p⁶3s²3p⁶3d⁸4s²
Copper	29	[Ar]3d¹⁰4s¹^*	₁₈Ar3d⁹	1+ Ar3d¹⁰
Zinc	30	1s²2s²2p⁶3s²3p⁶3d¹⁰4s²	₁₈Ar3d¹⁰	none

* Anomalous

Properties of the Elements - Table 2

Element	Metal (ionic ) radii / 10^-8 cm	1^st ionisation energy / kJ mol^-1	2^nd ionisation energy / kJ mol^-1	E^o_M²⁺/_M _{/ V}	density /g cm ^-3	melting point / ^oC
Chromium	1.29 (0.73)	653	1592	-0.41 Cr³⁺/Cr	7.20	1857
Managanese	1.37 (0.67)	715	1509	-1.19	7.20	1242
Iron	1.26 (0.61)	759	1561	-0.44	7.86	1535
Copper	1.28 (0.73)	746	1958	+0.34	8.92	1083
Zinc (3d¹⁰)	1.37 (0.75)	906	1733	-0.76	7.14	420
Calcium group II	1.97 (1.00)	590	1145	-2.87	1.54	839

Radii

· The radii are small for their atomic number. The radii are very similar within the d block This fact is dominant in the physical and chemical properties of the d block.

· Calcium, in the same period, is 51% larger than the average d block element.

· There is no uniform decrease in metallic radii across the period.

· The increasing nuclear charge does make the radii smaller, but the most important factor is the diffuse nature of the d orbitals. When the set of 5 d orbitals are not full they screen the 4s electrons very poorly from the nuclear charge. The effective nuclear charge is relatively large and radii decrease as the 4s electrons are attracted strongly to the nucleus.

· Note that Zn, with a full 3d shell, has a relatively large radius, given that it has the largest nuclear charge.

· The metallic radius is much greater than the ionic radius; since on forming a cation the outer shell of electrons is lost.

Ionisation energies I.E. and the formation of positive ions

· Both 1^st and 2^nd I.E. are large compared to Group I and II metals. This arises because of the diffuse nature of the d orbitals, poor screening, relatively large effective nuclear charges and small radii. See the discussion of radii above.

To read complete topic click here ................................