LECTURE 09 Metallic bonding

LECTURE 09 Metallic bonding - Dr. P. Lucas U of A MSE 110...

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Unformatted text preview: Dr. P. Lucas U of A MSE 110 Covalent Bonding SUMMARY FROM LAST CLASS Atoms with similar electronegativity form covalent bonds by combining and sharing two electrons into a molecular orbital delocalized over the two atomic nucleus. The σ bonding MO made by addition of two AO has low energy and contribute towards the covalent bond. σ = 1 s A + 1 s B The σ * antibonding MO made by subtraction of two AO has high energy and contributes against the bond. σ * = 1 s A - 1 s B The bond order is define as BO=½(e- in σ – e- in σ * ) and represent the number of covalent bonds between two atoms. The interaction of two p z AO generates σ and σ * MOs, while p x and p y generates π and π * MOs. O 2 has two unpaired electrons and is paramagnetic while N 2 has no unpaired electrons and is diamagnetic . Covalent bonds are very directional and have high bond strength, hence covalent solids formed from 3-D covalent network generate very hard materials such as diamond. Dr. P. Lucas U of A MSE 110 Metallic Elements: BONDING IN METALS All the pure elements from the left of the periodic table are metals while the rest are covalent. Metals are electrical conductors while metalloids are semiconductors and nonmetals are insulators. Dr. P. Lucas U of A MSE 110 Metallic bonds A simple model for metallic bonding is the free electron gas model . BONDING IN METALS Na [1s 2 2s 2 2p 6 3s 1 ] Æ Na + [1s 2 2s 2 2p 6 3s ] + e- In this model the valence electrons form a “sea” or gas of free electrons around the metal cations cores (Na + ) . Hence, one of the most defining characteristics of metals is their high electrical conductivity ....
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This note was uploaded on 10/06/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at Arizona.

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LECTURE 09 Metallic bonding - Dr. P. Lucas U of A MSE 110...

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