Difference Between Metallic And Covalent Bonding
Metallic bonding is the electrostatic force of attraction between positive ions known as cations and delocalised electrons in the ‘sea’ of electrons. When the ions form they release their valence electrons, these electrons are no longer bound to any specific atom and become a part of the delocalised sea. While the electrons are free to move the cations are fixed in place, this is depicted in figure 1. Covalent bonding is different to metallic bonding because instead of a bond between ions and delocalised electrons it is the bond formed by the electrostatic force of attraction between the positive nuclei of the atoms and shared electrons. Also the electrons and ions are not free to move.
An example of a …show more content…
This is done by bombarding or “doping” the silicon lattice with other atoms.
By doping the silicon with atoms that have one more valence electron than what it has an “n-type” semiconductor is produced. Silicon is found in group 16 and only has four valence electrons therefore by doping it with atoms that have five valence electrons such as Phosphorus the fifth electron does not form a covalent bond with the silicon atoms, refer to figure 7. Instead it is free to flow and become a part of the electric current.
“P-type” materials are created by doping the silicon with atoms that have one less valence electron than what it has, for example Boron (refer to figure 8), therefore would only have three electrons in its outer shell. Since there is only three available electrons to form covalent bonds with four valance silicon electrons, an electron hole is formed. The electron hole attracts electrons from other atoms and therefore creates another hole, this is how the electric current flows. Below figure 9 shows a diagram of n-type and p-type silicon and depicts the extra electron as well as the electron …show more content…
When these particles hit the silicon valence electrons they deposit discrete amounts of energy that the electrons absorb. This means that the photons have a certain amount of energy and the electrons can only absorb that exact amount, they cannot only absorb half. The energy from the photons allows the electrons to break free from the orbit of their atoms.
The energy of a photon is calculated by the equation, E_photon=hf , where ‘h’ is the symbol for Planck’s constant that equals 6.626×〖10〗^(-34) J.s and ‘f’ is the frequency in Hertz of the electromagnetic wave.
Because different types of electromagnetic waves have different frequencies it affects the photoelectric effect. For example, referring to figure 10, photons with higher frequencies that are on the left side of the spectrum have more energy and therefore make the electron come flying off the silicon atom faster. However the electromagnetic radiations with lower frequencies may not have enough energy to knock an electron out of orbit from its atom.
When electrons are knocked off their silicon atoms they need to be gathered into an electric current which is done by the imbalance within the PV cell created by N-type and P-type doping. This allows the electrons to flow throughout the cell and carry energy. The constant supply of energy from the bombardment of photons is what sustains this flow of