Our Solar System

Essay by Anonymous UserCollege, UndergraduateA+, November 1996

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12th grade essay on chemical bonds in our solar system. Well Researched!

Solar cells today are mostly made of silicon, one of the most common elements on Earth.

The crystalline silicon solar cell was one of the first types to be developed and it is still the most

common type in use today. They do not pollute the atmosphere and they leave behind no harmful

waste products. Photovoltaic cells work effectively even in cloudy weather and unlike solar

heaters, are more efficient at low temperatures. They do their job silently and there are no

moving parts to wear out. It is no wonder that one marvels on how such a device would


To understand how a solar cell works, it is necessary to go back to some basic atomic

concepts. In the simplest model of the atom, electrons orbit a central nucleus, composed of

protons and neutrons. each electron carries one negative charge and each proton one positive

charge. Neutrons carry no charge. Every atom has the same number of electrons as there are

protons, so, on the whole, it is electrically neutral. The electrons have discrete kinetic energy

levels, which increase with the orbital radius. When atoms bond together to form a solid, the

electron energy levels merge into bands. In electrical conductors, these bands are continuous but

in insulators and semiconductors there is an 'energy gap', in which no electron orbits can exist,

between the inner valence band and outer conduction band [Book 1]. Valence electrons help to

bind together the atoms in a solid by orbiting 2 adjacent nucleii, while conduction electrons,

being less closely bound to the nucleii, are free to move in response to an applied voltage or

electric field. The fewer conduction electrons there are, the higher the electrical resistivity of

the material.