Name: Atomic Structure: Protons, Neutrons and Electrons
Uploaded: 2019-03-11T09:20:58
Description: Learn by watching this video about Atomic Structure: Protons, Neutrons and Electrons at JoVE.com

<p>Elements are substances with unique physical and chemical properties that cannot be broken down into other substances by chemical reactions. Each element, like potassium, consists of a unique type of atom that differs from the atoms of other elements. These differences are found in the subatomic particles that make up each atom.</p>

<p>Two of these particle types are clustered in a central nucleus. Protons are positively charged while neutrons are uncharged, neutral. While both contribute to the mass, carrying one atomic mass unit each, it&#39;s the number of protons that determines the specific element, referred to as the atomic number.</p>

<p>Electrons, a third type of subatomic particle, are negatively charged and move rapidly in a cloud around the nucleus. This cloud is mostly empty space and makes up the vast majority of an atom&#39;s volume. Electrons remain near the nucleus because they are attracted to the positive charge of protons.</p>

<p>Generally, an atom contains an equal number of protons and electrons, which cancels out the positive and negative charges, leading to no net charge. However, depending on the electron configuration, they can be unstable as single atoms. In this case, they can lose electrons and become positively charged ions called cations or gain electrons and become more negative anions.</p>

atomic structure

<h4>Overview</h4>

<p>All matter is composed of atoms, the smallest individual units of elements. Each atom is made up of three subatomic particles: protons, neutrons, and electrons. Together, these three particles account for the mass and the charge of an atom.</p>

<h4>The History of Atomic Theory</h4>

<p>The first person to propose that everything on Earth is made up of tiny particles was the Greek philosopher Democritus, around 450 B.C. He used the term <em>atomos</em>, Greek for &ldquo;indivisible,&rdquo; from which the modern term &ldquo;atom&rdquo; is derived. His idea was not taken seriously at the time, however, and it was many centuries before the concept of the atom would be revived. In the 19th century, John Dalton proposed the atomic theory that is still largely correct today. He put forth five postulates to explain how atoms made up the world around us: (1) all matter is composed of infinitely small particles, or atoms; (2) all atoms of a given element are identical to one another and (3) are different from the atoms of all other elements; (4) two or more elements can combine in a fixed ratio to form a compound; and (5) atoms cannot be created or destroyed in a chemical reaction, but they can be rearranged to form new substances.</p>

<h4>Discovering the Subatomic Particles that Make up the Atom</h4>

<p>Dalton was only partially correct about the particles that make up matter. While atoms cannot be broken down further by ordinary chemical or physical processes, they are composed of three smaller subatomic particles. The first clue about the subatomic structure came at the end of the 19th century when J.J. Thomson discovered the electron. Scientists knew that the overall charge of an atom was neutral, but Thomson&rsquo;s &ldquo;plum pudding model&rdquo; of the atom attempted to reconcile this new information regarding the existence of a negatively-charged particle, suggesting that electrons were found studded throughout an area of positive charge. Just a few years later, Ernest Rutherford performed an experiment showing that most of an atom&rsquo;s mass is concentrated in the nucleus, where protons account for an atom&rsquo;s positive charge, and the tiny negatively-charged electrons make up most of the space outside of the nucleus. This disproved Thomson&rsquo;s plum pudding model and brought scientists one step closer to the familiar model of the atom we know today. The neutron was discovered later, in 1932, by James Chadwick. This final piece of the puzzle meant that scientists had now accounted for all the mass present in an atom with protons and neutrons, and all of its charge with protons and electrons.</p>

<h4>The Structure of an Atom</h4>

<p>Protons are found in the nucleus of an atom, have a positive charge, and a mass of one atomic mass unit (AMU) each. The number of protons is equal to the atomic number on the periodic table and determines the identity of the element. Neutrons are also found in the nucleus. They have no charge, but they have the same mass as protons and thus contribute to the atomic mass of an atom. Electrons orbit around the nucleus in clouds. They have a negative charge and negligible mass, so they contribute to the overall charge of an atom, but not to its mass.</p>

Learn by watching this video about Atomic Structure: Protons, Neutrons and Electrons at JoVE.com