Proton

Proton, elementary particle that carries a positive electric charge and, along with the electron and the neutron, is one of the building blocks of all atoms. Elementary particles are the smallest parts of matter that scientists can isolate. The proton is one of the few elementary particles that is stable—that is, it can exist by itself for a long period of time. Protons and neutrons are the building blocks of the atomic nucleus, the center of the atom. Electrons form the outer part of the atom. Protons have a positive electrical charge of 1.602 x 10-19 coulomb. This charge is equal but opposite to the negative charge of the electron. Neutrons have no electrical charge. Protons have a mass of 1.67 x 10-27 kg and, along with neutrons, they account for most of the mass in atoms. Atoms contain an equal number of protons and electrons so that every atom has an overall charge of zero.(See also Atom and Electricity)

The number of protons in the nucleus of an atom determines what kind of chemical element it is. All substances in nature are made up of combinations of the 92 different chemical elements, substances that cannot be broken into simpler substances by chemical processes. The atom is the smallest part of a chemical element that still retains the properties of the element. The number of protons in each atom can range from one in the hydrogen atom to 92 in the uranium atom, the heaviest naturally occurring element. (In the laboratory, scientists have created elements with as many as 116 protons in each nucleus.) The atomic number of an element is equal to the number of protons in each atom’s nucleus. The number of electrons in an uncharged atom must be equal to the number of protons, and the arrangement of these electrons determines the chemical properties of the atom.

STRUCTURE AND CHARACTERISTICS

The proton is 1,836 times as heavy as the electron. For an atom of hydrogen, which contains one electron and one proton, the proton provides 99.95 percent of the mass. The neutron weighs a little more than the proton. Elements heavier than hydrogen usually contain about the same number of protons and neutrons in their nuclei, so the atomic mass, or the mass of one atom, is usually about twice the atomic number.

Protons are affected by all four of the fundamental forces that govern all interactions between particles and energy in the universe. The electromagnetic force arises from matter carrying an electrical charge. It causes positively charged protons to attract negatively charged electrons and holds them in orbit around the nucleus of the atom. This force also makes the closely packed protons within the atomic nucleus repel each other with a force that is 100 million times stronger than the electrical attraction that binds the electrons. This repulsion is overcome, however, by the strong nuclear force, which binds the protons and neutrons together into a compact nucleus. The other two fundamental forces, gravitation and the weak nuclear force, also affect the proton. Gravitation is a force that attracts anything with mass (such as the proton) to every other thing in the universe that has mass. It is weak when the masses are small, but can become very large when the masses are great. The weak nuclear force is a feeble force that occurs between certain types of elementary particles, including the proton, and governs how some elementary particles break up into other particles.

Neutron

Neutron, electrically neutral elementary particle that is part of the nucleus of the atom. Elementary particles are the smallest parts of matter that scientists can isolate. The neutron is about 10-13 cm in diameter and weighs 1.6749 x 10-27 kg. See also Atom.

Neutrons and protons bind tightly together to create atomic nuclei. The number of protons an atom contains determines which chemical element it is, ranging from 1 proton for hydrogen to 92 for uranium, the largest naturally occurring element. Each atom usually contains about as many neutrons as protons, but different atoms of the same element may have different numbers of neutrons.

Atoms that differ only in the number of neutrons are called isotopes. For example, most atoms of the simplest element, hydrogen, have a nucleus containing only a single proton. In natural hydrogen, however, 0.015 percent of the atoms have a neutron in addition to the proton. This isotope is called heavy hydrogen or deuterium. An element usually has several isotopes, all nearly identical in the way they react chemically with other elements and each other. Scientists can distinguish different isotopes of an element by examining properties of the element’s nuclei, such as the mass of the nucleus.

CHARACTERISTICS

The neutron is slightly heavier than a proton and 1,838 times as heavy as the electron. It is affected by all the four fundamental forces of nature. Because it has mass, it is affected by gravitation, the force of attraction between all objects in the universe. Although the neutron has no electrical charge, it is slightly magnetic, so it is affected by the electromagnetic force, the force of attraction or repulsion between electrically charged or magnetic objects. The neutron is affected by the strong nuclear force, an attraction that binds the neutron to protons and other neutrons in the nucleus. The neutron is also affected by the weak nuclear force, an interaction among the building blocks of the neutron that causes the neutron to decay, or break apart. Isolated from nuclear matter, a free neutron decays into a positively charged proton and a negatively charged electron, releasing energy in the process (see Nuclear Energy). The average lifetime of a free neutron is just under 15 minutes.

Electron

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.