Result in a Continuous Flow of Charge or Current Through the Configuration
Last Updated on March 19, 2021 by
In order to study electronics effectively, you should first have a basic understanding of electrical charge and how an electrical charge moves through a conductor as electrical current. In this post, we will discuss the concept of electrical charge and current at the atomic level using the Bohr model. The Bohr model presents the structure of an atom much like a solar system where the planets are orbiting the sun. This makes it rather easy to understand the concept of an atom, electrical charge and current flow.
After reading this post, you should have a basic understanding of:
• the structure of an atom,
• an electrical charge,
• an atom's atomic weight and number,
• electron orbits and energy bands,
• conductors and insulators, and
• current flow.
The Atom
The most basic component of all matter is the atom. Using the basic Bohr model, we can agree that all atoms are made up of three fundamental and distinct particles.
These are:
• Neutrons
• Protons
• Electrons
Neutrons and protons are considered the heaviest particles in the atom. Neutrons and protons make up the nucleus, or the center, of the atom. Electrons, however, are about 1/1800th the weight of a neutron and the electron orbits the atoms nucleus. When an atom is electrically balanced, it contains an equal number of electrons and protons. The atom is referred to as an ion when it has a net positive or negative charge after loosing or gaining one or more electrons.
Electrical Charge
There are two types of electrical charge. If you are familiar with a basic battery, you will know that it has a positive (+) and negative (-) terminal. These terminals are akin to a positive and negative electrical charge. In terms of the atom, neutrons have no charge, protons have a positive charge and electrons have a negative charge.
Electrons are kept in orbit around the atom's nucleus by an electrostatic force of attraction between the protons, at the core of the atom, and the orbiting electrons itself. This is because particles with the same charge repel each other while oppositely charged particles attract each other.
Atomic Number
The number of neutrons, protons and electrons in the atoms that make up an element varies depending on the type of element. Aluminum, for example has 14 neutrons, 13 protons and 13 electrons. While zinc, on the other hand, has 35 neutrons, 30 protons and 30 electrons.
The atomic number of an atom is given by the number of protons in its nucleus. This means that aluminum has an atonic number of 13 and zinc has an atomic number of 30. The atomic number of an atom should not be confused with its atomic weight.
The atomic weight of an atom is obtained by summing the number of neutrons and protons in its atom's nucleus. Aluminum has an atomic weight of 14 neutrons + 13 protons = 27 while zinc has an atomic weight of 35 neutrons + 30 protons = 65. The atomic weight of an atom is typically referred to as its atomic mass.
One element that is of particular relevance to our discussion on electrical current is copper. Copper is a metal commonly used in electrical conductors to carry electrical current. The atomic number for copper is 29. Copper has 29 protons in its nucleus (along with 35 neutrons) and 29 orbiting electrons ─ when not an ion.
Electron Orbits and Energy Bands
For each individual atom, there is only a certain number of orbits available in which electrons can travel. Each of these orbits are grouped in a specific energy band and only a certain number of electrons can exist in each energy band at any one time.
There is also an energy gap between each energy band that cannot be occupied by the orbiting electrons. The configuration of electron orbits grouped into energy bands, as well as band gaps and the maximum number of electrons for each band, applies to all atoms.
The innermost energy band of an atom can hold only two electrons. The second energy band can hold eight and the third band can hold only 18 before the electrons move into the next band outward.
For an understanding of current flow, we need only concern ourselves with the outermost energy bands, as that is where the electrons are the furthest away from the nucleus, under the least influence from electrostatic force and contain the most energy. The two outermost energy bands are known as the valance and conduction bands – in that order.
Electrons orbiting in the valance band of the atom contain more energy than the atoms in the inner bands. The electrons in the inner orbits are more tightly bound to the protons in the nucleus by electrostatic force. These electrons are much more difficult to knock free from the atoms valance band into the conduction band and thus do not play a meaningful role in current flow.
The electrons in the valance band, however, contains much more energy and are less tightly bound to the nucleus. These electrons are more easily moved into the conduction band where they can participate in current flow.
Electrons are moved into the conduction band by applying energy in the form of heat, light, or the electromotive force from a power source.
Conductors and Insulators
Elements make good conductors when their atoms have many electrons in the conduction band. Elements are good insulators, that is they make poor conductors, when there are very few electrons in the conduction band.
Conductors
As mentioned above, copper is an example of a good conductor. Copper has one electron in its valance shell separated by 28 electrons distributed through its inner shells. The electron in the valance shell is the farthest removed from the nucleus and experiences the least force of attraction to the nucleus. Additionally, the energy gap between the valance and conduction band in a good conductor like copper is nonextant. In fact, the bands are often overlapping makes it easily move electrons from the valance band into the conduction band. Thus, the energy introduced to the atom by room temperature alone is enough to keep many electrons in the conduction band.
Insulators
A good insulator has a wide gap between its valance and conduction bands. This makes it difficult for electrons in the valance band to move into the conduction band. A good electrical insulator would also have its valance band fully occupied by electrons. Remember that energy bands can hold a maximum number of electrons. Therefore, when the valance band is at its maximum capacity, and there are no additional electrons to move to the next band outward, its electrons are locked into place by covalent bonding to the atoms in the material around them.
Current Flow
In an electrical circuit, current flow is achieved by applying energy in the form of heat, light, or electromotive force from a power source to a conductor.
Current flow defined as the amount of charge that moves pass a certain point in one second. One ampere of current is equivalent to one coulomb passing a specific point in one second. One coulomb is equivalent to 6.25 X 1018 electrons. Therefore, 1 ampere is equal to 6.25 X 1018 electrons passing through a specific point in a circuit in one second.
Source: https://circuitground.com/understanding-electrical-charge-and-current-flow/
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