Otis Singleton
Electrons are fundamental particles that carry a negative electric charge. They are a crucial component of atoms, which are electrically neutral due to the balance between the positive charge of protons and the negative charge of electrons. Atoms can become charged and transition into ions if they gain or lose electrons. The movement of electrons in conductors, such as metal wires, generates electric currents, and the flow of electrons in circuits powers various electronic devices. The concept of electric charge, including the classification of charges as positive or negative, was introduced by Benjamin Franklin, although the choice of terminology was arbitrary.
| Characteristics | Values |
|---|---|
| Charge | Negative |
| Electric field | Produced by electrons |
| Magnetic field | Produced by moving electrons |
| Behaviour in an electromagnetic field | Determined by the total amount of charge and the charge distribution of an object |
| Designation of charge | Historical convention |
| Behaviour with similar charges | Repel each other |
| Behaviour with opposite charges | Attract each other |
| Shells | Divided into subshells, with the number of subshells increasing with distance from the nucleus |
| Energy levels | Increase with distance from the nucleus |
| Quantum behaviour | Exist as both particles and waves, allowing them to tunnel through barriers |
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What You'll Learn
Electrons are negatively charged particles
Electrons are found in shells surrounding the nucleus of an atom. These shells are similar to the layers in the Earth's atmosphere, with the electrons existing as both particles and waves due to quantum mechanics. Electrons can occupy different energy levels within these shells, with their energy increasing as they move further from the nucleus. The outermost shells of an atom are crucial in determining its reactivity with other elements. When an atom has an equal number of protons and electrons, the positive and negative charges cancel each other out, resulting in a net charge of zero, making the atom electrically neutral.
However, atoms can gain or lose electrons, becoming charged ions. When an atom loses an electron, it gains a net positive charge due to the remaining unneutralized protons in the nucleus. Conversely, when an atom gains an electron, it acquires a net negative charge. This process of gaining or losing electrons is known as ionization, and it plays a significant role in various chemical and physical phenomena, including the behaviour of electric currents in metal wires and the functioning of batteries.
The movement of electrons within a material can also lead to static electricity. When dissimilar materials, such as amber and fur or glass and silk, are rubbed together, electrons can transfer from one material to the other, creating an imbalance of charges. This phenomenon is described by Coulomb's law, which states that the force between two charged particles is proportional to the product of their charges and inversely proportional to the square of the distance between them.
In summary, electrons are negatively charged particles that play a crucial role in the structure of atoms and the behaviour of electric charges and currents. Their negative charge, as defined by convention, is fundamental to understanding the interactions between particles and the properties of matter at the atomic and macroscopic levels.
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Protons are positively charged
Electrons are defined as having a negative charge. This is in contrast to protons, which are positively charged. Benjamin Franklin defined positive and negative charges before the particles were discovered. He defined the charge acquired by a glass rod when it is rubbed with silk cloth as positive.
The positive charge of protons is fundamental to their interaction with electrons. Charged particles with the same sign repel one another, while those with different signs attract. This means that protons and electrons attract each other. This attraction is quantified by Coulomb's law, which states that the force between two particles is proportional to the product of their charges and inversely proportional to the square of the distance between them.
The positive charge of protons is also important to their role in atoms. Atoms are generally electrically neutral because they contain equal numbers of protons and electrons, so the positive and negative charges cancel each other out. However, if an atom gains or loses electrons, it becomes charged and is referred to as an ion. For example, if a carbon atom with 6 protons loses an electron, it becomes a cation with a positive charge of +1.
The positive charge of protons is not just a matter of convention. While the labels of electric and magnetic charges are due to convention, the underlying charges of protons and electrons are not. The charges of these particles are fundamental properties that can be described mathematically. For example, the total charge of a proton can be calculated as the sum of the charges of its constituent quarks.
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Electrons surround the nucleus in shells
Electrons carry a negative charge and orbit around the nucleus of an atom in various energy levels. The existence of electron shells was first observed experimentally by Charles Barkla and Henry Moseley through X-ray absorption studies. The electron shells are divided into subshells, and each subshell consists of one or more atomic orbitals. The shells are similar to the different layers in the Earth's atmosphere, with each shell capable of holding a different number of electrons.
In 1913, Niels Bohr proposed a model of the atom, suggesting the arrangement of electrons in sequential orbits. Bohr's model allowed the capacity of the inner orbit of the atom to increase to eight electrons as the atoms got larger. Arnold Sommerfeld modified Bohr's model, introducing the term "shell". Walther Kossel, who worked with Bohr, used the term "shell" in his papers in 1914 and 1916.
The shells are labelled with the letters K, L, M, N, O, P, and Q. The terminology was derived alphabetically, with the innermost shell being labelled K, and the subsequent shells following the alphabetical order. Each shell can hold a maximum of two electrons in the first shell, eight in the next, and so on. The outermost shells can hold more electrons, and electrons in these shells have higher energy levels.
When electrons gain energy and move to a higher shell, they become "excited". When they return to their original shells and "relax", they emit a photon. The wavelength of the photon depends on how far the electron falls back toward the atom's nucleus. This process is important in understanding the properties of atoms and their behaviour, such as their reactivity with other elements.
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Electrons can tunnel and appear on the opposite side of a barrier
Electrons are subatomic particles that carry a negative charge. Protons, on the other hand, carry a positive charge, while neutrons are neutral and have no charge. Atoms are electrically neutral because they contain equal numbers of protons and electrons, with the positive and negative charges balancing each other out.
Electrons can "tunnel" and appear on the opposite side of a barrier through a phenomenon called quantum tunnelling. This occurs when an electron passes through a potential energy barrier that, according to classical mechanics, it should not be able to pass through due to not having sufficient energy. However, electrons are both particles and waves, and part of a wave can be on the other side of a barrier. This phenomenon is observed in modern integrated circuits and electron microscopes.
Quantum tunnelling is a consequence of the wave nature of matter, where the quantum wave function describes the state of a particle or physical system. The probability of an electron tunnelling through a barrier is influenced by factors such as the barrier's height, width, and the particle's mass. The probability of transmission decreases exponentially with these factors. For example, the probability of tunnelling is higher for low-mass particles such as electrons or protons passing through microscopically narrow barriers.
The concept of quantum tunnelling was first explored theoretically in 1927 by Friedrich Hund, shortly after the publication of the Schrödinger equation. In 1928, Leonid Mandelstam and Mikhail Leontovich independently published their findings on quantum tunnelling. The term "tunnel effect" was introduced in 1932 by Yakov Frenkel, and in 1957, Leo Esaki demonstrated the tunnelling of electrons over a few nanometre-wide barriers in a semiconductor structure. This led to the development of a diode based on the tunnel effect, for which Esaki shared the 1973 Nobel Prize in Physics.
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Electrons can separate from atoms
Electrons carry a negative charge and surround the nucleus of an atom. The number of electrons in an atom is usually equal to the number of protons, which carry a positive charge. This balance results in an atom with a net charge of zero, making it electrically neutral. However, electrons can separate from atoms, and when this happens, the atom becomes charged and is referred to as an ion.
When electrons gain energy, they can move to higher energy shells or even escape the atom, becoming free or separated from it. This process, known as ionization, results in the creation of a positively charged ion since the electron that has been removed carries a negative charge. Ionization can occur through various methods, such as providing sufficient energy to the electron or using ionizing radiation like X-rays and gamma rays, which have enough energy to free electrons from atoms.
Another way to separate electrons from atoms is through thermionic emission. When an object is heated and placed in a vacuum, it emits electrons, similar to how it emits photons. This phenomenon is not a rare event and is utilized in tube televisions, vacuum tube amplifiers, and electron guns in cathode ray tubes (CRTs) for older TVs and monitors.
The separation of electrons from atoms is also observed in conducting metals, where electrons drift around, usually in the direction of current flow. Additionally, electrons can tunnel and appear on the opposite side of a barrier due to their dual nature as both particles and waves. This phenomenon, known as quantum tunneling, is applied in electron microscopes and modern integrated circuits.
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Frequently asked questions
Electrons are subatomic particles that surround the nucleus of an atom. Electrons are arranged in shells, or layers, around the nucleus. Electrons can tunnel and appear on the opposite side of a barrier, a phenomenon called quantum tunnelling.
Electrons are electrically negative. Protons are positively charged and are located in the nucleus (the centre) of the atom, while electrons are negatively charged and orbit around the nucleus in various energy levels.
The designation of electrons as negative is a matter of convention. Benjamin Franklin defined positive and negative charges before the discovery of protons and electrons. He defined a positive charge as the charge acquired by a glass rod when it is rubbed with a silk cloth.
Charged particles with the same sign repel one another, and particles with different signs attract. When an atom has the same number of protons and electrons, the positive charge from the protons balances out the negative charge from the electrons, resulting in an overall charge of zero, which means the atom is electrically neutral.
