Electricity and the Atomic Model !

Electricity and the Atomic Model !
Electricity and the Atomic Model !
Electricity and the Atomic Model !
Electricity and the Atomic Model !
Electricity and the Atomic Model !
Electricity and the Atomic Model !

Nature and effects of electricity:

The meaning of the word "electricity"

Electricity is a term that covers all the phenomena caused either by static electric charge or by the movement of charge (current) and the electrical and magnetic fields associated with that. Electricity is commonly understood to be a form of energy comparable to other energy forms such as heat, light, mechanical or chemical energy. Electrical energy has some major advantages over other forms of energy, however:

Electrical energy can be easily conveyed over long distances. Power stations supply large areas via overhead transmission cables.

Electrical energy can easily be converted into other forms of energy, e.g. heat, light or mechanical energy. It is therefore used commonly both domestically and in industry.

Natural electrical phenomena:

Probably the best known and most spectacular appearance of electricity is in the form of lightning. Lightning involves a discharge of high electrostatic voltages generated by friction between storm clouds. Such a discharge involves the motion of both positive and negative charges. Electricity also occurs in less obvious forms, however. For example, the transmission of information through the human nervous system is partially based on electrical signals. Certain types of fish like the electric eel (bottom right) can also generate high voltages for the purpose of defence. They can also detect electrical signals generated by the muscle movement of other fish and use these to locate prey. 

Effects of electricity on the human body:

Electricity can have a variety of effects on the human body depending on its strength. The decisive factor in terms of its effect on the body is the current. Low currents are sometimes used to accelerate healing processes in a technique known as electrotherapy, or can provide pulse signals for a cardiac pacemaker. Larger currents may even revive a heart that has stopped beating when applied with a so-called defibrillator (pictured right). Higher currents in excess of abut 50 mA can be dangerous and even deadly. An electric shock stun gun, for example, shoots a series of powerful electrical signals through a victim that cause painful, uncontrollable muscle spasms. At the extreme end of the scale, very high current may be intentionally used to kill, as in the case of the electric chair. 

Atomic Models:

All electrical states and processes are linked to the presence of the tiniest of all elementary particles that is known as an electron.

An electron carries a charge that corresponds to the smallest amount of electrical charge it is possible to have. It is the elementary quantum of electricity.

Electrons are a constituent of the atoms that make up any chemical element. An atom (from the Greek atomos, meaning irreducible) was long thought to be the ultimate irreducible component of matter. Nowadays it is known that atoms are not irreducible. They actually possess a rather complex structure that we have tried to envisage using atomic models. The atomic model developed by Niels Bohr is still the most important of these. It perceives the structure of an atom as being in the nature of our solar system. At the centre lies the atomic nucleus in the way that the sun lies at the centre of the solar system. Electrons then move in orbit around this nucleus like planets. Atoms of various elements differ in terms of the size of the nucleus and the number of electrons that surround it. The electron orbits can be elliptical or circular and are of differing diameter and in differing planes. They make up the shell of the atom. The diameter of an atomic nucleus is about 10,000 times smaller than the diameter of the atom as a whole.

Atoms consist of an atomic nucleus and an electron shell.

Electrons are negatively charged while the nucleus is composed of uncharged neutrons and positively charged protons. Its overall charge is thus positive. For this reason, an atom should possess an equal number of electrons and protons to make it electrically neutral. The following graphic depicts the atomic model in its entirety. 

The simplest atom is that of the lightest element hydrogen. This has only one electron orbiting a single proton with no neutrons at all. An atom of oxygen, for example, would possess eight electrons, two in an inner orbital shell and six further out. An aluminium atom contains 13 electrons in three different orbital shells of differing diameter. The heaviest atom known to occur naturally is that of uranium, which has 92 electrons in seven separate orbital shells. The following graphic depicts simplified models of the hydrogen, oxygen and aluminium atoms. The orbits are shown as if they were circular and in the same plane for simplicity's sake and the structures of the nuclei themselves are also omitted. 

Each electron orbit can only accommodate a specific maximum number of of electrons. The innermost orbital shell can only contain two electrons, the next layer has a maximum of eight and the third takes up to 18. 

Conductors and insulators:

The conductivity of a material is effectively related to the number of free electrons in it. A distinction is usually made between conductors, insulators and semiconductors, which have a special role of their own.

Conductors:

Electric current can only occur in materials that contain charge carriers (usually free electrons) that are free to move within the substance. Those materials that contain many such free electrons that are able to move with little resistance are called conductors of electricity. The following graphic depicts the movement of free electrons between the atoms of a conductor.  

Solid conductors are most likely to be metals, such as gold, silver, copper, aluminium or iron. One non-metallic conductor is the graphite form of carbon. Liquids can also conduct electricity, for instance metallic mercury, indeed any molten metal, or aqueous solutions of salts, acids and bases.

Insulators:

Materials that contain very few free electrons are usually called non-conductors or insulators. They can conduct next to no current. The following graphic illustrates why this is. 

Among the solid materials that do not conduct well are glass, porcelain, amber, rubber, paper, cotton and plastics. They are thus suitable for insulating one conductor from another. These substances do, however, possess a certain, albeit slight, conductivity, i.e. there are no perfect insulators. For this reason there is no actual well-defined boundary between conductors and insulators. Instead there exists a continuous spectrum of conductivity.

Semiconductors:

Materials that fall into the category of semiconductors occupy a special position between conductors and insulators. They are particularly important in the manufacture of electronic components such as diodes, transistors and integrated circuits. The main materials with the requisite properties are silicon and germanium. The conductivity of these matrials can be altered by a process called doping, which introduces impurities into a substance that can lead either to a surplus of free electrons or a relative absence of them. The absence of an electron results in a so-called hole in the atomic lattice. Those free electrons that do exist can sometimes fill a hole but this then leaves a gap elsewhere, so that it appears that the holes themselves are moving through the substance. This kind of movement of holes can be thought of as carrying a charge in a similar way to the free electrons themselves. Holes regarded in this way are considered to be carrying a positive charge in contrast to the negative charge carried by electrons. The following graphic shows how the two types of charge carrier move in a semiconductor of this kind. 

Free Electrons:

As we have already seen, electrons move around an atomic sheel in various discrete orbital paths at varying distances from the nucleus. Each of these paths represents a shell where the electron has a specific energy. The higher the energy, the greater the radius of the orbital path. Electrons in the outermost shell thus have the highest amount of energy and are less closely bound to the atom than electrons in the inner shells. Electrons such as these are called valence electrons. The exchange of these electrons is responsible for the formation of an atomic lattice. The way an element's atoms bond together depends on how the valence electrons of each atom can become linked in pairs. This linking of atoms gives rise to characteristic properties of the element that are dependent on the valence electrons of individual atoms in the atomic lattice.

The following graphic depicts a simplified model of a copper atom. It has two atoms in the first and innermost shell, eight electrons in the second shell, eighteen in the third and one valence electron in its outermost shell. 

Since valence electrons are only weakly bound to the atomic nucleus, a sufficient quantity´of energy can cause them to leave their orbit altogether, so that they are no longer part of the atom at all. This leads to the phenomenon of free electrons. These can effectively move more or less freely from one atom to the next within the atomic lattice of a substance. These free electrons play a key role in the conductivity of materials.

Applications of electricity:

Technical uses of electricity

The word electricity often evokes the danger that can be associated with plugs or electrical equipment. Protecting oneself against this risk is easier the more one knows about processes and laws over the wide spectrum that electricity covers. Such knowledge is essential in view of the wide variety of technical applications for electricity that we nowadays take for granted. Imagine if the power stations were to shut down for a whole day. Electric trains, electric or even oil-fired central heating, refrigerators, lifts, traffic lights and electric lighting would all fail. Hospitals, telephone exchanges and water-supply pumping stations all have to have back-up power supplies for this event. 

For more than a hundred years, applications of electricity for lighting, heating and power have increasingly influenced human life. This ever-increasing importance is being furthered even more in view of the electrical energy needed nowadays for communications and information technology.

Example - electric locomotives:

The example of electric locomotives (pictured right) reveals the vital importance of electricity in our day and age. Not only the propulsion of the locomotive but also the lighting and heating of the train, the brakes and safety equipment and even the cooking in the buffet kitchen are all accomplished using electricity. For trains to run safely on an extensive and complex railway network, a mass of electrical remote control, signalling and radio communications equipment is needed and electricity is also used to operate points and lighting systems etc. 

Generation and transmission of electrical energy:

Most of the electrical energy consumed nowadays comes from generators in power stations. Various primary energy supplies are used as fuel (e.g. coal or gas). Electricity can also be produced from chemical energy in batteries and accumulators. The relatively new technology of photo-voltaics utilises the photo-electric effect by means of solar cells (pictured right) that generate power by converting sunlight into electrical energy. 

Electrical energy is mostly conveyed as a result of the movement of electrons in solid bodies. To achieve such transmission of energy, cables are manufactured from materials with low specific resisitivity (usually metals). The unavoidable losses that occur in the transmission of electricity can be reduced by employing very high voltages. High-tension electric cables, for example, are operated at voltages in a range between 10 and 380 kV. Since electrical energy is commonly generated in power stations and must be conveyed to loads large distances away, the actual transmission of the electricity has a major influence on the effectiveness of the entire power supply network. 

More From Iamtechnical.com

Advertisement: