Electrons are negatively charged subatomic particles that, along with protons and neutrons, make up atoms. They are involved in chemical bonding, electricity, and the solidity of objects. Electrons can behave like waves and are arranged in shells around atoms. Chemical elements’ properties depend on the number and arrangement of electrons. Atoms combine to form molecules through ionic or covalent bonding. Electricity is the movement of electrons, and conductors like metals allow for easy electron movement. The term “electron” was first used in 1919, and its charge was measured in 1894 by Robert Andrews Millikan.
An electron is a subatomic particle with a negative electric charge equal to, but opposite to, the positive charge of a proton. These two particles, together with the neutrons, form the atoms, with the protons and neutrons residing in the nucleus and the electrons in the surrounding orbitals, held in place by the electromagnetic force. They are involved in chemical bonding, can flow through some materials as an electric current, and are responsible for the solidity of solid objects. The particles have a tiny mass, about 1/1836 the mass of a proton, and are thought to be fundamental—that is, not made up of smaller components.
While it’s often convenient to think of electrons as tiny, point-like particles, they can, in common with other subatomic particles, sometimes behave like waves. This is known as wave-particle duality. Since no one can actually see an electron, even using the most powerful and sensitive instruments available, it is only possible to build models to try to explain its behavior. In some cases a “particle” model works better, in others a “wave” model. Most of the time, however, these entities are referred to as particles.
Electrons in everyday life
Electrons play a vital role in everything humans experience on a daily basis. Their mutual electrical repulsion prevents solid objects from passing through each other, despite the fact that the atoms the objects are made of are mostly empty spaces. These particles are also responsible for allowing atoms to come together to form the molecules that make up the Earth and life itself. Modern civilization and technology are heavily dependent on electricity, which involves the movement of electrons.
Atoms, elements and molecules
The properties of chemical elements depend on the number of electrons they have and their arrangement within the atom. These factors determine how the atoms of an element combine with other atoms to form molecules. When atoms combine, they combine in such a way that they reach a lower energy level. Electrons can be thought of as arranged in concentric shells, each with a maximum number it can hold. Usually, the lowest energy state is achieved between two atoms when both are able to fill their outermost shells.
There are two main ways atoms can combine or form a chemical bond with each other. In ionic bonding, one atom donates one or more electrons to another atom of a different element, usually in such a way that both reach their complete outer shells. Since an atom normally has the same number of electrons as protons, it is electrically neutral, but losing or gaining some will give it a positive or negative charge, forming an ion. A metal will tend to donate electrons to a nonmetal to form an ionic compound. The molecule is held together by the electrical attraction between the positively charged metal and the negatively charged nonmetal.
In a covalent bond — which forms between nonmetals — atoms combine by sharing electrons to reach a lower energy state, usually, again, filling their outer shells. For example, a carbon atom, which is four fewer than a complete outer shell, can form covalent bonds with four hydrogen atoms, each one electron short, forming a molecule of methane (CH4). In this way, all five atoms share a complete shell. Covalent bonds hold together the complex organic molecules that are essential for life.
Electrical systems
The movement of electrons from one place to another manifests itself as electricity. This can take the form of ‘static’ electricity, where friction causes these particles to move from one material to another, leaving both electrically charged and able to exert an attraction towards other objects. This was first documented in ancient Greece, when the effect was produced by rubbing amber with fur. The word electron, in fact, comes from the Greek word for amber.
A device called a Van de Graff generator uses this effect to generate very high voltages that can produce large sparks.
The most familiar form of electricity, however, is the electric current that is supplied to homes and industry to provide light and heat, and to power various devices and processes. It consists of a flow of electrons through a suitable material, known as a conductor. The best conductors are metals, because their outer electrons are held freely and can move around easily. The movement of a conductor within a magnetic field can produce a flow of electrons within it, an effect that is used in large-scale electricity generation.
History
The idea that electricity could come in small indivisible units had been around since the first half of the 19th century, but it was in 1919 that Irish physicist G. Johnstone Stoney first used the term electron to describe the postulated fundamental unit of negative electric charge. Three years later, British physicist JJ Thompson identified it as a subatomic particle. It was not until 1894 that its charge was measured by Robert Andrews Millikan, an American experimental physicist, with an ingenious experiment well known to physics students. He suspended oil droplets of various sizes in an adjustable electric field and calculated the amounts of charge needed to keep them from falling under gravity. It turned out that the values were all multiples of the same tiny unit, which was the charge on a single electron.
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