Electron

I

Introduction

Electron, negatively charged particle found in an atom. Electrons, along with neutrons and protons, comprise the basic building blocks of all atoms. The electrons form the outer layer or layers of an atom, while the neutrons and protons make up the nucleus, or core, of the atom. Electrons, neutrons, and protons are elementary particles—that is, they are among the smallest parts of matter that scientists can isolate. The electron carries a negative electric charge of –1.602 x 10-¹⁹ coulomb and has a mass of 9.109 x 10-³¹ kg. See also Atom.

Electrons are responsible for many important physical phenomena, such as electricity and light, and for physical and chemical properties of matter. Electrons form electric currents by flowing in a stream and carrying their negative charge with them. All electrical devices, from flashlights to computers, depend on the movement of electrons. Electrons also are involved in creating light. The electrons in the outer layers of the atom sometimes lose energy, emitting the energy in the form of light. Because electrons form the outer layers of atoms, they are also responsible for many of the physical and chemical properties of the chemical elements. Electrons help determine how atoms of an element behave with respect to each other and how they react with atoms of other elements. See also Chemistry.

II

Electrons as Elementary Particles

The electron is one of the most fundamental and most important of elementary particles. The electron is also one of the few elementary particles that is stable, meaning it can exist by itself for a long period of time. Most other elementary particles can exist independently for only a fraction of a second.

Electrons are among the smallest of all elementary particles and have no detectable shape or structure. At the same time, they do have a property that scientists can measure called spin, or intrinsic angular momentum. An electron’s spin makes it act as a tiny magnet. Electrons can spin clockwise or counterclockwise.

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The electron is affected by three of the four fundamental forces that define the nature and interaction of everything in the universe: gravitation, the electromagnetic force, and the weak nuclear force. Gravitation is the attractive force between every object in the universe that has mass. Gravitation affects the electron because the electron has mass. The electromagnetic force affects objects with an electric charge, so the electron’s negative electric charge subjects it to the forces of electromagnetism. The electron attracts positively charged particles, such as protons, and repels negatively charged particles, such as other electrons. The electron is also sensitive to the weak nuclear force, a very feeble force that affects certain types of elementary particles and is only important over very short distances. The one fundamental force that does not affect the electron is the strong nuclear force, which is the force that binds protons and neutrons in the atom’s nucleus.

III

Electrons in Atoms

An atom consists of neutrons and protons packed into a dense nucleus with electrons orbiting around the nucleus. The neutrons have no electrical charge, while each proton carries a positive charge that is equal and opposite to the negative charge of the electron. Each chemical element is defined by the number of protons in the nucleus of its atoms; this number is the element’s atomic number. The electrons are equal in number to the protons in the atom, balancing the electrical charge of the nucleus. In other words, the atom’s net charge is zero, and the atom is said to be neutral.

A

Electron Orbitals

Scientists cannot simultaneously measure both the exact location of an electron and its precise speed and direction, so they cannot measure the path a specific electron takes as it orbits the nucleus. The law of physics governing this phenomenon is called the uncertainty principle. Scientists can, however, determine the area an electron will probably occupy, and the probability of finding the electron at some place inside this area. A map of this area and its probabilities forms a cloudlike pattern known as an orbital. Each orbital can contain two electrons, but these electrons can not have identical properties, so they must spin in opposite directions. Orbitals are grouped into shells, like the layers of an onion, around the nucleus. Each shell can contain a limited number of orbitals, which means that each shell can contain a limited number of electrons. Each shell corresponds to a certain level of energy, and all the electrons in the shell have this same level of energy. As the shells get farther from the nucleus, they can contain more electrons, and the electrons in the shells have higher energy. See also Chemistry: Electron Cloud.

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