Chemical Bonding Essay

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Metallic bonding is a type of chemical bonding formed in the metals, it is a result of electromagnetism. It is an attraction between positive charged metal ions and electrons in a sea of valence electrons. It is also described as the sharing of free electrons among positive charged ions in the substance with a crystal structure. In this structure, electrons are not bonded to any particular atom and they are free to move in the solid metal. This fact results in the conductivity of metal.

Covalent Bonding

Between non-metal atoms, atoms are combined together by sharing electrons, this type of chemical bonding is called Covalent bonding. It is the stable force between positive nuclei and valence elections. Atoms will covalently bond with other
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It has 14 protons and 14 neutrons in its nucleus, 3 electron shells, including 4 valence electrons available for chemical reaction.


Silicon is an element in group VA, period 3 and with an atomic number of 5. It has 15 protons and 16 neutrons in its nucleus, 3 electron shells, including 5 valence electrons available for chemical reaction.

2. P-type and N-type doping

Doping is a process of adding dopant atoms to an intrinsic (pure) semiconductor in order to modulate its electrical properties. It normally introduces impurities to silicon (Si) or germanium (Ge) because they have 4 valence electrons and the atoms form a crystal structure. Doped semiconductors act more like a conductor than a semiconductor. The type of impurities determines the type of doped semiconductor. There are two types of doping:


The addition of impurities such as boron (B), aluminum (Al) or gallium (Ga) which has 3 valence electrons creates deficiencies of valence electrons, forms excess holes in the lattice. These holes are considered to be positive charged, therefore they will accept free electrons when current passes through. Due to these acceptors, P-type semiconductors have better conductivity than pure
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Light Dependent Resistors (LDR’s)

Light dependent resistor (LDR) or photoresistor is a light-controlled resistor. It is made of high resistance semiconductor, and very light intensity. The resistance when unilluminated is up to several megohms (MΩ) and drops to about 100Ω when illuminated (see Figure 7-1).

In the dark, there are very few free electrons in the semiconductor. When light strikes the material, photon energies are absorbed and transferred to the electrons. These excited electrons have enough energies to overcome the energy gap and jump into the conduction band, these process releases free electrons and decreases the resistance of the material.
LDR can be applied in many light-sensitive circuits such as street lamps, camera light meters, security alarms and outdoor clocks, which contains a LDR switch that can be turned on in the light and off in the dark (see Figure 7-2).

7. Passive InfraRed Motion Sensors (PIR’s)

A passive infrared motion sensor is a device that receives and measures infrared from objects in order to detect a motion.
Every object with a temperature above absolute zero emit energy in the form of radiation. The radiation is usually in the wavelength of infrared so it is invisible to human

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