January 13 1 Transition Metals, Properties

23.1 Metals and Metallurgy

Transition Metal Chemistry

Fred Omega Garces Chemistry 201 Miramar College

January 13 2 Transition Metals, Properties

Earth radius (6370 km, 10192 mi) Deepest well - 8 Km (12.8 mi) mines - 4 Km (6.4 mi) Most of our metals found in concentrated deposits known as Ore Ore - mixture of materials Metallurgy - Science of extracting metals and the studying and manipulation of their properties.

Earth -Stratosphere - Lithosphere

Troposphere!Stratosphere!Mesosphere!

Lithosphere

January 13 3 Transition Metals, Properties

History is divided by composition of tools used in that period- Stone Age, Bronze Age, Iron Age, ...

• Today iron is not the dominant metal for industry anymore.

• A jet engine is composed of - Ti, Ni, Cr, Co, Al,Nb, Tl

• Similarly the best golf clubs is made out of Ti, Zr, B or some alloy.

History Timeline

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Metallic Bonding

Physical Properties of Metals Important physical properties of pure metals: Malleable, ductile, good conductors, and feel cold.

Most metals are solids with the atoms in a close packed arrangement.

In Cu each atom is surrounded by 12 neighbors.

There are not enough electrons for the metal atoms to be covalently bonded to each other.

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Properties of Metal Theories describing properties & behavior.

VBT (electron - sea model) Electron-sea model proposes: -Delocalized model for electrons in a metal.

MO (Bond Theory) Delocalized model by Overlap of atomic orbitals

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VBT (electron - sea model) Valence orbital overlap such that e- are free to migrate.

The metal nuclei exist in a sea of electrons. No e- localized between any two metal atoms. Therefore, the electrons can flow freely. Without any definite bonds,

metals easy to deform (and are malleable and ductile). High e- conductivity an heat capacity (heat conductor)

Electron Sea model: metal bonds parallel number of valence electron, the greater the valence electrons, the greater the bond strength.

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Draw Back of VBT

Problems with the electron sea model: • As the number of electrons increase, the strength of bonding should increase and the melting point should increase.

But: • Group 6B metals have the highest melting points (center of the transition metals).

Sc g Cr g Zn

Increase melting point ...highest for Cr. ...then decrease melting point, …contrary to Theory.

January 13 8 Transition Metals, Properties

MO (band Theory) MO is a more qualitative approach. This theory treats bonding in terms of bonding and antibonding. Classic MO Theory. Consider Chromium:

[Cr] = 4s1 3d5 Bond Order = 6 Electron fills bonding orbital, highest bond order is when all bonding orbital are occupied and there are no antibonding contributions.

January 13 9 Transition Metals, Properties

MO for transition metal MO explains bond strength trend Sc BO = 1 to Cr BO = 6

e-fill bonding orbital (low BO to high BO) Cr BO = 6 to Zn BO = 1

e- fill anti-bonding (high BO to low BO) e- free to roam under thermal conditions

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MO For Insulator

Next available orbital not available for e-, therefore e- are immobilized.

Large gap therefore e- can’t be promoted

January 13 11 Transition Metals, Properties

Transition metals characterized by incomplete d-orbitals d-orbitals lead to multiple oxidation states.

Zeff slowly increase resulting in lower oxidation states for later transition elements. (Since Zeff larger for latter transition metals, it is more difficult to remove e- therefore latter elements can’t attain high Ox. number.)

Sc (+3) ...Cr (+ 2...+6)...Mn (+2...+7)....Zn (+3) Note Zn has the smallest ionic radii, and largest Zeff

Transition Metals and Valence e-

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Atomic Radius Similar trend going down Period (2nd and 3rd row transition metal) Note: Going down pt, expect Atomic radii to decrease: Sc<Y<La For Ti, Zr, Hf, this pattern doesn’t follow trend Ti < Zr = Hf. Why?

The size systematically decreases going across the periodic table until the 8B family, and then the atomic radii increases again.

January 13 13 Transition Metals, Properties

• Between La and Hf, Z = 57 to 72, and the number of

protons increases resulting in increase in Zeff The increase in Zeff for Hf, offset the increase in n when going from Zr to Hf, therefore Zr and Hf are about the same size.

Lanthanide contraction

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Other Properties

Some miscellaneous properties for the fourth period transition elements.

January 13 15 Transition Metals, Properties

Magnetism

Presence of unpaired of e- lead to interesting magnetic properties diamagnetic, no unpaired e-, actually is repelled

by magnetic. field paramagnetic- presence of unpaired e-. will be

influence by strong magnetic. field. Attraction

ferromagnetic - also presence of unpaired e- except that in there are domains in solid that permanently align selves in presence of magnetic field.

Ferromagnetic 1•106 more magnetic than paramagnetic material

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Metals, Metalloid & Nonmetals

The properties of elements in terms of their metallic character. The d-block elements lose their valence s-electrons when they form compounds. Moreover, most of them can also lose a variable number of d-electrons, and hence show variable valence. Variable valence makes these elements useful as catalysts and, in bio-molecular chemicals