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Chapter 4: Chemical Bonding, Metallic Bond, Hydrogen bonds are formed when…
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Metallic Bond
Electron Sea Model
The metallic bond consists of atoms held together by their valence electrons that are moving freely throughout the structure in 3-dimensions
The electrons are detached from their parent atoms and are frequently referred to as an electron sea
The atoms are held together by strong forces of attraction between the positive nuclei and the delocalised electrons
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Electrical conductivity
Electrons carry electrical charges by flowing freely through a metallic structure (crossing grain boundaries)
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The Band Theory
In the basic MO theory, atomic orbitals on two atoms would combine to form bonding and antibonding orbitals
Expanding the idea by considering combinations of 10 atoms, a set of five bonding and five antibonding orbitals would be obtained
If a large number of atoms combine, a large number of bonding and antibonding orbitals will be formed so close together in energy that they create bands of bonding and antibonding orbitals
An insulator has a large band gap between bandsAn insulator has very low electrical conductivity, but the conductivity increases with an increase in temperature
A semiconductor has a small band gapSemiconductors show electrical conductivity that increases with increasing temperature, opposite to that of metals
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Hydrogen bonds are formed when partially positively charged hydrogen atoms in water are attracted to partially negatively charged oxygen atoms in cellulose.When the hair is wet, there are hydrogen bonds between water molecules and quarantine in the outer layer of the hair. As a result, the hair becomes sticky.
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