Atoms, Molecules and Electronics
Bear in mind that this a simplified discussion of the elements. Reality is a bit more complicated. Our intention here is the study of the behavior of electrons. This study we call electronics. This is a very condensed course. In a college we might spend a month on this subject. In a technical school we might spend a week. Here we are going to spend about one hour. College is certainly a better education. A technical school (like a Slot Tech School) would be second best. This is intended to cover only the minimal knowledge accepotable to learn basic concepts and is not iintended to cover everything you might get in a Technical School or College.
Defining atoms (that define an element) and molecules (that define a compound)
Everything around us that has substance is made of atoms. If we take a chunk of Aluminum and start breaking it apart into smaller and smaller pieces, the smallest thing we could break it into, and still have something identifiable as Aluminum, would be an atom of Aluminum. All atoms of Aluminum are identical in size and structure. We can not break Aluminum down into any other identifiable materials. This makes Aluminum a basic element.
(picture of an atom, exterior view)
We have identified about one hundred basic elements that make up everything around us. Water, for instance, is made of Hydrogen and Oxygen. If we take water apart into smaller and smaller units. The smallest unit that would be identifiable as water would be a group of two atoms of Hydrogen and one atom of Oxygen, designated H2O. This is one molecule of water. These substances are called compounds.
(picture of a molecule)
Atoms and molecules are the smallest identifiable objects we can identify. Molecules break down into atoms, but once we break an atom apart we cease to have anything we can identify as a substance. Sub-atomic particles are primarily just globs of energy.
All atoms are made of a central core, called a nucleus, surrounded by a shell of electrons. Electrons from an Aluminum atom are the same as electrons from Hydrogen or Oxygen atoms.
(picture of an atom showing parts)
The nucleus is made of Protons and Neutrons. All protons are identical. All Neutrons are identical. Around this central core is layers of electrons flyiing around in what can best be described as orbits. The only thing that makes Aluminum different from Oxygen or Hydrogen is the number of Electrons, Protons, and Neutrons that make up the atoms.
Hydrogen, for example, is the most basic element. An atom of Hydrogen has a nucleus of one proton with one electron circling around it. All hydrogen atoms are made this way, and everything made this way must be hydrogen.
(picture of Hydrogen)
The next heaviest element is Helium, which has two protons in the nucleus, surrounded by two electrons. All helium atoms are made this way, and everything made this way must be helium.
(picture of Helium)
All elements can be referred to by their structural makeup. Hydrogen has just one proton, so it is given the Atomic Number “1”. It has only one proton in it’s nucleus, so it given the Atomic Weight of “1”. There are always (normally) an equal number of electrons as there are protons. Helium has an Atomic Number of “2”, having two protons. Helium has an Atomic Weight of “4”. The nucleus of Helium has two protons and
Two neutrons, the sum of the parts in the nucleus is what defines the Atomic Weight. Every element has a unique Atomic Number and Atomic Weight. This is not a perfect reality. Every element also has variations of it that may have more or less neutrons in the nucleus than the norm would be. These are called isotopes of that element.
The Atomic number covers a range from one to over one hundred, but atomic diameter varies much less. Hydrogen, the smallest of the elements. At STPG (Standard Temperature Pressure and Gravity) Hydrogen has a diameter of 0.53 Angstroms. Francium, the largest element I have data for, with an atomic number of 87 only has a diameter of 2.7 Angstroms. Only five times the diameter of Hydrogen. (*)
Almost all of the mass of an atom is in the nucleus. An electron is about the same size as a proton or neutron, if you can imagine a cloud having a physical size. But the electron has only about 1/1800th the mass of a proton or neutron.
Electrons have a negative electrostatic charge. Protons have a positive electrostatic charge. It is this electrostatic charge that we will spend some time discussing. Neutrons are neutral, and have no charge, and play no part in our study of Electricity. An electron is mostly electromagnetic energy and it is the study of the behavior of electrons we will primarily concern ourselves with.
The normal atom, having an equal number of negative electrons and positive protons, has no electrical charge. It is this characteristic we will alter as we discuss electricity. If we remove an electron from an atom, it now has more positively charged protons than negatively charged electrons, and the atom becomes a positive ion, a charged atom. Likewise, if we force an extra electron onto an atom it now has more electrons than protons, and becomes a negative ion.
For our purposes, we are concerned with the outer shell of electrons. An electron is mostly energy with very little mass. Electrons move around the nucleus is loosely defined shells at extremely high speeds (186,000 miles per second, or 300,000 kilometers per second). The structure of these shells defines many characteristics the element will have.
The electrons are layered in predictable shells and subshells. It is the outer shell, called the Valence Shell, of electrons that is of particular interest to us in the study of electricity. If the outer shell has only one or two electrons, they may be pulled away and move to a neighboring atom with relative ease. This is what makes an element a good conductor of electricity. These are primarily metals.
If the outer shell is complete and stable (with eight eectrons), the electrons are not readily pulled out of place. These elements are insulators, and do not conduct electricity well.
These last two statements are true whether we are talking about an element or a molecule. If a molecule has one or two loosely bonded electrons, it will be a good conductor. If not, it will be a good insulator.
In between the extremes of conductors and insulators are a group of elements (or molecules) that have four or five electrons in the outer shell. These are semiconductors. They are neither good conductors, nor good insulators. By controlling the specific characteristics of these elements we can get some very creative results. This is the realm of Solid State Electronics.
Conductors, like metals, are used to carry electricity from one point to another. Insulators are used to prevent the flow of electricity where we don't want it to go. Semiconductors are used to specifically manipulate the flow of electricity in detail.
Some popular semiconductors are elements like Carbon, Selenium, Silicon, and Germanium, or compounds like Cadmium Sulfide, and Gallium Arsenide. The list of useful molecular compounds is extensive. By including various elements, we can get unique characteristics that cause light to be emitted (Gallium Arsenic, or Gallium Arsenic Phosphide), or cause the compound to react to the presence of light (Cadmium Sulfide). We can create substances that change shape on the application of electricity, or create electricity by the application of physical pressure.
What we have said concerning what makes an atom a conductor or insulator also applies to molecules. While a metal, like Iron, mixes with Oxygen to make iron oxide, the result is an insulator. The outer electrons of the Iron atoms are tied up in bonds to the Oxygen atoms. Rust (iron oxide) is a poor conductor.
The possibilities are limited only by the laws of physics, our understanding of the elements and the imagination we apply in manipulating the laws of physics.
Electricity and Electronics
Electricity is the flow of electrons, and the accompanying things that happen when an electron moves through a conductor. Electronics is the detailed study of how electrons flow, and all the wonderful things that happen in solid state physics.
Current, Voltage, and Resistance.
The Intensity of current flow (I) is measured in Amps (Amperes). This is a measure of how many electrons are in motion at any specific point in a circuit.
The electrical pressure pushing the electrons through a circuit is measured in Volts. This is sometimes called Electromotive Force (EMF), because that is a good description of what it is - the force that moves the electrons.
Normally, in an atom, we have an equal number of electrons and protons. The electrical charge of the atom is neutral. When an electron is pulled away from an atom, it leaves a tension in the atom. The atom now has a positive charge (from the missing electron). This tension is the source of pressure we call voltage. This positively charged atom sucks at the nearby environment, attracting an electron, causing current to flow.
The opposition to current flow is Resistance. Resistance is measured in Ohms. As we mentioned, some elements require more pressure before we can get an electron to cut loose from its bond to the atom. The harder it is to pull an electron away, the more resistance the material has.
(The following analogy between water flow and electron flow is useful in learning the basic concepts, but be mindful that this analogy develops flaws as you get into the finer details of solid state electronics.)
Current, Voltage, and Resistance can be visualized as water flowing through a pipe. The larger the pipe is, the easier water can flow through the pipe. More water can be carried through a larger pipe. Likewise, larger wire is required to carry higher current levels.
The pressure pushing water through the pipe is analogous to the voltage applied in a circuit. By exerting more pressure, higher current can be caused to flow through a given circuit. For higher pressures, thicker pipes, or pipes of stronger material, are required. Likewise, higher voltage requires insulators of high resistance, or thicker material.
The opposition to the flow of water through a pipe is analogous to electrical resistance. Thinner pipe resists the flow of large amounts of water. Smaller wire has a higher resistance than larger wire. A pipe with a filter, or blockage, inhibits water flow. Semiconductors, such as carbon or metal oxides, resist current flow and allow us to tailor the current flow to a specific desirable value.
In a conductor the electrons in the outer shell of the atoms (called the Valence shell) are in constant motion, but moving in no particular order. As one of the loose electrons (called Valence electrons) moves from one atom towards another, the atom also attracts an electron from another neighboring atom onto the atom it just left, and pushes an electron off of the atom it is moving to.
We can look at a voltage from either point of view; a negative voltage pushing electrons; or a positive voltage sucking electrons. The difference is only relative. Voltage is a difference of a potential to move electrons between two points in a circuit.
A conductor can be looked at as having a Sea of Electrons available to allow current flow. All we have to do is apply pressure to get current to flow in the direction we choose. Getting back to our analogy to water. We can view a glass of water, full to the brim, as a conductor. If left alone the water molecules can move aimlessly around in the glass, but no organized flow is apparent. When we add pressure to the water by inserting our finger into the glass, water flows out of the glass in proportion to the force and volume we exert.
Polarity
As mentioned before, electrons have a negative charge. As we insert an electron into a conductor, it repels a neighboring electron, which pushes on this sea of electrons. Almost instantly, on the opposite end of the conductor, another electron is forced out. This force moves down the wire at the speed of light, 186,000 miles per second, or 300,000 kilometers per second, if you prefer.
A force that pushes electrons is called Negative. A force that attracts an electron is called Positive. To have current flow we have to a difference of potential force between two places in a circuit. Electrons flow from a Negative voltage to a Positive voltage. Negative and Positive need only be of relative values.
How we view current flow can be viewed from two perspectives. We can say electrons flow from negative to positive, and be quite correct. For every electron that moves from negative to positive, we have a hole where that electron was that sucks in a neighboring electron. If we view the electron as moving from left to right through a line of electrons, we can also allow the point of view that a hole moves from right to left. Conventional current flow (hole flow) can be said to move from positive to negative.
If you learn electricity in a chemistry or physics class, you were probably taught that electricity flows from positive to negative. Such was the story when Ben Franklin flew his kite. As we got into the twentieth century and discovered what was inside the atom, the concept of the electron changes our opinion of what electricity was.
We must understand that both of these are happening at the same time, it is only a matter of how we look at what is happening. If we take a bottle of water with a narrow neck and dump it into a sink do you see bubbles flowing upwards or water flowing downward? One can not happen without the other. Such is current flow. Whether you look at it as electrons (negative charges) flowing from negative to positive, or holes (positive charges) flowing from positive to negative makes no difference. When we get to solid state devices, you must consider and understand both concepts.