Electron

Electrons


The chemist's notion of physical reality is based on the existence of two particles that are smaller than atoms. These particles are the proton and the electron (a neutron is just a combination of the two). While there are sub-subatomic particles (quarks, hadrons, and the like), protons and electrons in some sense represent the simplest particles necessary to describe matter.

The electron was discovered early in the 20th Century. Electrons are very light (2,000 times lighter than the smallest atom, hydrogen) and have a negative charge. Protons, which make up the rest of the mass of hydrogen, have a positive charge. When two electrons come near one another, they interact by the fundamental electrical force law. This force can be expressed by a simple equation that is sometimes called Coulomb's law.

For two charged particles separated by a distance r, the force acting between them is given as

F = Q1Q2/r2

Here F is the force acting between the two particles separated by a distance r, and the charges on the particles are, respectively, Q1 and Q2. Notice that if both particles are electrons, then both Q1 and Q2 have the same sign (as well as the same value); therefore, F is a positive number. When a positive force acts on a particle, it pushes it away. Two electrons do not like coming near one another because "like charges repel" just as two north-polarized magnets do not like to approach each other. The opposite is also true. If you have two particles with opposite charges, the force between them will be negative. They will attract each other, so unlike charges attract. This follows directly from Coulomb's law.


It also follows from Coulomb's law that the force of interaction is small if the particles get very far apart (so that r becomes very big). Therefore, two electrons right near one another will push away from one another until they are separated by such a long distance that the force between them becomes irrelevant, and they relax into solipsistic bliss.




Bonds are key to nanotechnology. They combine atoms and ions into molecules and can themselves act as mechanical devices like hinges, bearings, or structural members for machines that are nanoscale. For microscale and larger devices, bonds are just a means of creating materials and reactions. At the nanoscale, where molecules may themselves be devices, bonds may also be device components.

Traditionally, materials science has been devoted to three large classes of materials—metals, polymers, and ceramics.

Metals: Atoms like to cluster with others of the same kind. This process can make huge molecule-like structures containing many billions of billions of atoms of the same sort. In most cases, these become hard, shiny, ductile structures called metals. In metals, some of the electrons can leave their individual atoms and flow through the bulk of the metal.

Polymers: The most common polymers are plastics. Most polymers are based on carbon because carbon has an almost unique ability to bond to itself. Polymers are single molecules formed of repeating patterns of atoms (called monomers) connected in a chain.

Ceramics: The last area of traditional materials science is ceramics. Ceramics are often but not always oxides, which are structures where one of the atoms making up the extended structure is oxygen.



Coulomb's law
The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.
wikipedia.org


Skin effect
In a Direct Current circuit, the electrons travel evenly through the entire cross section of the conductor. however, in an AC circuit conductor, besides setting up eddy currents, the voltage that creates the eddy current also causes the current flow in the conductor to be repelled away from the centre of the conductor toward the outside of he conductor. The current is forced to travel near the surface of the conductor. This effect, known as the skin effect, creates the same consequence as reducing the cross sectional area of the conductor because the electrons are forced to flow in a smaller area concentrated near the surface of the conductor. the skin effect also causes an increase in the conductor resistance in the circuit due to power losses. Both eddy currents and the skin effect are directly related to the frequency of the circuit. Therefore, as the frequency increases the magnitude of the eddy currents increases causing the skin effect to also increase.
AC Theory, Thomson, NY, 2004