{"id":23305,"date":"2019-04-30T07:43:18","date_gmt":"2019-04-30T07:43:18","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=23305"},"modified":"2023-06-07T11:01:57","modified_gmt":"2023-06-07T11:01:57","slug":"atom-properties-of-atoms","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/","title":{"rendered":"What is Atom &#8211; Properties of Atoms"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"sue-shadow-wrap sue-content-wrap sue-shadow-inline-no\"><div   id="8n9s8rpp6h"    class=\"sue-shadow sue-shadow-style-vertical\">\n<div   id="8n9s8rpp6h"    class=\"sue-panel\" data-url=\"\" data-target=\"self\" style=\"background-color:#ffffff;color:#333333;border-radius:0px;-moz-border-radius:0px;-webkit-border-radius:0px;box-shadow:none;-moz-box-shadow:none;-webkit-box-shadow:none;border:1px solid #cccccc\"><div   id="8n9s8rpp6h"    class=\"sue-panel-content sue-content-wrap\" style=\"padding:15px;text-align:left\">\n<div class=\"su-heading su-heading-style-modern-1-dark su-heading-align-left\" id=\"\" style=\"font-size:13px;margin-bottom:20px\"><div   id="8n9s8rpp6h"    class=\"su-heading-inner\">\n<h2>Atoms<\/h2>\n<\/div><\/div>\n<h3>What are atoms?<\/h3>\n<p><strong>The atoms<\/strong> are defined as the smallest constituents of ordinary matter, which can be divided without releasing electrically charged particles. The atoms consist of two parts, <strong>an\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/atomic-nucleus\/\">atomic nucleus<\/a>,<\/strong> and <strong>an <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-electron-properties-of-electron\/electron-cloud\/\">electron cloud<\/a><\/strong>.<\/p>\n<h3>Key Facts<\/h3>\n<ul>\n<li>The physical world is composed of combinations of various\u00a0<strong>subatomic or <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/\">fundamental particles<\/a><\/strong>, and these\u00a0are the smallest building blocks of matter.<\/li>\n<li>The <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/\">atoms<\/a> consist of two parts, <strong>an\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/atomic-nucleus\/\">atomic nucleus<\/a>,<\/strong>\u00a0and\u00a0<strong>an\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-electron-properties-of-electron\/electron-cloud\/\">electron cloud<\/a><\/strong>.<\/li>\n<li>The number of electrons and their arrangement in the electron cloud is responsible for the chemical behavior of atoms.<\/li>\n<li>The\u00a0<strong>nuclear properties<\/strong>\u00a0(atomic mass,\u00a0<a href=\"http:\/\/sitepourvtc.com\/neutron-cross-section\/\">nuclear cross-sections<\/a>) of the element are determined by the\u00a0<strong>number of protons<\/strong>\u00a0(<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atomic-nuclear-structure\/atomic-number-proton-number\/\">atomic number<\/a>) and the <strong>number of neutrons\u00a0<\/strong>(<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atomic-nuclear-structure\/neutron-number\/\">neutron number<\/a>).<\/li>\n<li><a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/nuclear-stability\/\"><strong>Nuclear stability<\/strong><\/a>\u00a0is a concept that helps to identify the stability of an <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/nuclides\/isotope\/\">isotope<\/a>. It is needed to find the ratio of <a title=\"Neutron\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/\" target=\"_blank\" rel=\"noopener\">neutrons<\/a> to protons to identify the stability of an isotope. To determine the stability of an isotope, you can use the ratio neutron\/proton (N\/Z).<\/li>\n<li>There are only certain combinations of neutrons and protons which form <strong>stable nuclei<\/strong>.<\/li>\n<li><strong>Unstable nuclei<\/strong> must undergo <a href=\"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/\"><strong>nuclear<\/strong><\/a><strong><a href=\"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/\"> decay<\/a> (radioactive decay)<\/strong> to stabilize themselves, and it is a random and natural process.<\/li>\n<li>The number of atoms in<strong>\u00a01 mole<\/strong> (e.g., 12 grams of carbon) of a substance is equal to the\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/ideal-gas-law\/gas-laws\/avogadros-constant-avogadros-number\/\"><strong>Avogadro\u2019s constant<\/strong><\/a>, equal to<strong> 6.022 x 10<sup>23<\/sup>.<\/strong><\/li>\n<\/ul>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:10px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\">\n<div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-modern-light su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>What is the size of an atom?<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>What is the size of an atom?<\/strong><\/p>\n<p>The atoms are about 10<sup>&#8211;<\/sup><sup>10<\/sup>\u00a0<b>meters<\/b>\u00a0(or 10<sup>&#8211;<\/sup><sup>8<\/sup> centimeters) in size, corresponding to the angstrom. The \u00e5ngstr\u00f6m is not a part of the SI system of units, but it can generally be considered part of the metric system. <strong>The volume of an atom<\/strong>\u00a0is about\u00a0<strong>15 orders of magnitude<\/strong>\u00a0<strong>larger<\/strong>\u00a0than the volume of a nucleus. For\u00a0<strong>uranium atom<\/strong>, the\u00a0<strong>Van der Waals radius<\/strong>\u00a0is about\u00a0<strong>186 pm = 1.86 \u00d710<sup>\u221210<\/sup>\u00a0m<\/strong>.<\/p>\n<p>It must be noted that atoms lack a well-defined outer boundary. The atomic radius of a chemical element measures the distance out to which the electron cloud extends from the nucleus. However, this assumes the atom exhibits a spherical shape, which is only obeyed for atoms in a vacuum or free space. Therefore, there are various non-equivalent definitions of atomic radius.<\/p>\n<ul>\n<li><strong>Van der Waals radius. <\/strong>In principle, Vana der Waals radius is half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule.<\/li>\n<li><strong>Ionic radius. <\/strong>An ionic radius is one-half the distance between the nuclei of two ions in an ionic bond.<\/li>\n<li><strong>Covalent radius. <\/strong>A covalent\u00a0radius is the nominal radius of the atoms of an element when covalently bound to other atoms.<\/li>\n<li><strong>Metallic radius. <\/strong>A metallic radius is one-half the distance between the nuclei of two adjacent atoms in a crystalline structure when joined to other atoms by metallic bonds.<\/li>\n<\/ul>\n<\/div><\/div>\n<div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-modern-light su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Why are atoms radioactive?<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<p><strong>Why are atoms radioactive?<\/strong><\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/atomic-nucleus\/\">Atomic nuclei<\/a>\u00a0consist of protons and neutrons, which attract each other through\u00a0<strong>the\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-interactions-fundamental-forces\/strong-interaction-strong-force\/nuclear-force-residual-strong-force\/\">nuclear force<\/a><\/strong>, while protons repel each other via\u00a0<strong>the\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-interactions-fundamental-forces\/electromagnetic-interaction-electromagnetic-force\/\">electric force<\/a><\/strong> due to their positive charge. These two forces compete, leading to various stability of nuclei. There are only certain combinations of neutrons and protons which form <strong>stable nuclei<\/strong>.<\/p>\n<p><strong>Neutrons stabilize the nucleus<\/strong> because they attract each other and protons, which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, <strong>an increasing ratio of neutrons to protons is needed<\/strong> to form a stable nucleus. If there are too many or too few neutrons for a given number of protons, the resulting nucleus is not stable and undergoes <a title=\"Radioactive decay \u2013 Nuclear Decay\" href=\"http:\/\/sitepourvtc.com\/radioactive-decay\/\">radioactive decay<\/a>. <strong>Unstable isotopes<\/strong> decay through various radioactive decay pathways, most commonly alpha decay, beta decay, or electron capture. Many other rare types of decay, such as spontaneous fission or neutron emission, are known. It should be noted that all of these decay pathways may be accompanied by <strong>the subsequent emission of\u00a0<a title=\"Gamma Rays \/ Gamma Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gamma radiation<\/a><\/strong>. Pure alpha or beta decays are very rare.<\/p>\n<\/div><\/div>\n<div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-modern-light su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Is an atom an empty space?<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<p><strong>Is an atom an empty space?<\/strong><\/p>\n<p>It may seem that the space and the matter are <strong>empty<\/strong>,\u00a0<strong>but it is not<\/strong>. Due to the <strong>quantum nature of electrons<\/strong>, the electrons are not pointing particles, and they are smeared out over the whole atom. The classical description cannot be used to describe things on the atomic scale. On the atomic scale, physicists have found that quantum mechanics describes things very well on that scale. Particle locations in quantum mechanics are not at an exact position, and they are described by a <strong>probability density function<\/strong>. Therefore the space in an atom (between electrons and an atomic nucleus) is not empty. Still, it is filled by a probability density function of electrons (usually known as \u201c<strong>electron cloud \u201c<\/strong>).<\/p>\n<\/div><\/div>\n<\/div>\n<\/div><\/div>\n<\/div><\/div>\n<p>The physical world is composed of combinations of various <strong>subatomic or fundamental particles<\/strong>. These are the smallest building blocks of <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-matter\/\">matter<\/a>. All matter except dark matter is made of molecules, which are themselves made of <strong>atoms<\/strong>. <strong>The atoms<\/strong> are the smallest constituents of ordinary matter, which can be divided without releasing electrically charged particles. The atoms consist of two parts. <strong>An atomic nucleus<\/strong> and <strong>an <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-electron-properties-of-electron\/electron-cloud\/\">electron cloud<\/a><\/strong>. The electrons are spinning around the atomic nucleus. The nucleus itself is generally made of protons and <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/\">neutrons<\/a>, but even these are composite objects. Inside the protons and neutrons, we find <strong>the <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/quarks\/\">quarks<\/a><\/strong>.<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/what-is-atom-properties.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-23306\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/what-is-atom-properties-300x205.png\" alt=\"What is Atom - Properties of Atoms\" width=\"300\" height=\"205\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/what-is-atom-properties-300x205.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/what-is-atom-properties-200x137.png 200w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/what-is-atom-properties-400x274.png 400w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/what-is-atom-properties.png 437w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>The science that deals with atoms are called atomic physics. Note that atomic and nuclear physics are not the same. The term atomic physics is often associated with nuclear power due to the synonymous use of atomic and nuclear in standard English. However, physicists distinguish between atomic and nuclear physics. <strong>Atomic physics<\/strong> deals with the atom as a system consisting of <strong>a nucleus and electrons<\/strong>. <strong>Nuclear physics<\/strong> deals with the nucleus as a system consisting of <strong>nucleons (protons and neutrons)<\/strong>. The main difference is in <strong>the scale<\/strong>. While the term atomic deals with 1\u00c5 = 10<sup>-10<\/sup>m, where \u00c5 is an \u00e5ngstr\u00f6m (according to Anders Jonas \u00c5ngstr\u00f6m), the \u00a0term nuclear deals with\u00a0 1femtometre = 1fermi = 10<sup>-15<\/sup>m.<\/p>\n<p><strong>Atomic physics<\/strong> is the field of physics that studies atoms as an isolated system of <strong>electrons and an atomic nucleus<\/strong>. It is primarily concerned with the arrangement of electrons around the nucleus and the processes by which these arrangements change. This includes ions as well as neutral atoms, and unless otherwise stated, for the purposes of this discussion, it should be assumed that the term atom includes ions. Atomic physics also helps to understand the physics of molecules, but molecular physics also describes the physical properties of molecules.<\/p>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/\"><strong>Atomic and Nuclear Physics<\/strong><\/a><\/p>\n<div   id="8n9s8rpp6h"    class=\"collapsible-container\">\n<h2>Properties of Atoms<\/h2>\n<p>Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. The chemical properties of the atom are determined by the number of protons, in fact, by the number and arrangement of electrons. The configuration of these electrons follows the principles of quantum mechanics. The number of electrons in each element\u2019s electron shells, particularly the outermost valence shell, is the primary factor determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.<\/p>\n<h2>Chemical Properties of Atoms<\/h2>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/09\/Proton-Number-Atomic-Number.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-18742\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/09\/Proton-Number-Atomic-Number-225x300.png\" alt=\"Proton Number - Atomic Number\" width=\"225\" height=\"300\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/09\/Proton-Number-Atomic-Number-225x300.png 225w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/09\/Proton-Number-Atomic-Number.png 723w\" sizes=\"(max-width: 225px) 100vw, 225px\" \/><\/a>The total number of protons in the nucleus of an atom is called the <strong>atomic number<\/strong> (or the <strong>proton number<\/strong>) of the atom and is given the symbol <strong>Z<\/strong>. The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the total electrical charge of the nucleus is <strong>+Ze<\/strong>, where e (elementary charge) equals <strong>1,602 x 10<\/strong><strong><sup>-19<\/sup><\/strong><strong>coulombs<\/strong>. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z \u2013 1) negative electrons in the atom.<\/p>\n<p>It is the Pauli exclusion principle that requires the electrons in an atom to occupy different energy levels instead of them all condensing in the ground state. The ordering of the electrons in the ground state of multielectron atoms starts with the lowest energy state (ground state). It moves progressively from there up the energy scale until each of the atom\u2019s electrons has been assigned a unique set of quantum numbers. This fact has key implications for building up the periodic table of elements.<\/p>\n<h2>Nuclear Properties<\/h2>\n<p>Properties of atomic nuclei (atomic mass,\u00a0<a title=\"Neutron Cross-section\" href=\"http:\/\/sitepourvtc.com\/neutron-cross-section\/\">nuclear cross-sections<\/a>) are determined by the number of protons and the <strong>number of neutrons\u00a0<\/strong>(neutron number). It must be noted especially nuclear cross-sections may vary by many orders from nuclide with the neutron number N to nuclide with the neutron number N+1. For example, actinides with odd neutron numbers are usually fissile (fissionable with slow neutrons), while actinides with even neutron numbers are not fissile (but fissionable with fast neutrons). Due to the Pauli exclusion principle, heavy nuclei with an even number of protons and an even number of neutrons are very stable thanks to the occurrence of \u2018paired spin.\u2019 On the other hand, nuclei with an odd number of protons and neutrons are mostly unstable.<\/p>\n<h3>Neutron and Atomic Numbers and Nuclear Stability<\/h3>\n<p><strong>Nuclear stability<\/strong> is a concept that helps to identify the stability of an isotope. It is needed to find the ratio of neutrons to protons to identify the stability of an isotope. To determine the stability of an isotope, you can use the ratio neutron\/proton (N\/Z). Also, to help understand this concept, there is a chart of the nuclides, known as a Segre chart. This chart shows a plot of the known nuclides as a function of their atomic and neutron numbers. It can be observed from the chart that there are <strong>more neutrons than protons<\/strong>\u00a0in nuclides with\u00a0<strong>Z greater<\/strong> than about 20 (Calcium). These\u00a0<strong>extra neutrons<\/strong> are necessary for the stability of the heavier nuclei. The excess neutrons act somewhat like nuclear glue. Only two stable nuclides have fewer neutrons than protons: hydrogen-1 and helium-3.<\/p>\n<figure id=\"attachment_11260\" aria-describedby=\"caption-attachment-11260\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/12\/nuclide_chart.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-11260\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/12\/nuclide_chart-300x195.jpg\" alt=\"Nuclide chart - Nuclear Stability\" width=\"300\" height=\"195\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/12\/nuclide_chart-300x195.jpg 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/12\/nuclide_chart-1024x668.jpg 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/12\/nuclide_chart.jpg 1913w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-11260\" class=\"wp-caption-text\">The Segre chart shows a plot of the known nuclides as a function of their atomic and neutron numbers. It can be observed from the chart that there are more neutrons than protons in nuclides with Z greater than about 20 (Calcium). These extra neutrons are necessary for the stability of the heavier nuclei, and the excess neutrons act somewhat like nuclear glue.<\/figcaption><\/figure>\n<p>Atomic nuclei consist of protons and neutrons, which attract each other through\u00a0<strong>the\u00a0nuclear force<\/strong>, while protons repel each other via\u00a0<strong>the\u00a0electric force<\/strong> due to their positive charge. These two forces compete, leading to various stability of nuclei. There are only certain combinations of neutrons and protons which form <strong>stable nuclei<\/strong>.<span id=\"ezoic-pub-ad-placeholder-114\" class=\"ezoic-adpicker-ad\"><\/span><\/p>\n<p><strong>Neutrons stabilize the nucleus<\/strong> because they attract each other and protons, which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, <strong>an increasing ratio of neutrons to protons is needed<\/strong> to form a stable nucleus. If there are too many or too few neutrons for a given number of protons, the resulting nucleus is not stable and undergoes <a title=\"Radioactive decay \u2013 Nuclear Decay\" href=\"http:\/\/sitepourvtc.com\/radioactive-decay\/\">radioactive decay<\/a>. <strong>Unstable isotopes\u00a0<\/strong>decay through various radioactive decay pathways, most commonly\u00a0<a href=\"https:\/\/www.radiation-dosimetry.org\/what-is-alpha-decay-alpha-radioactivity-definition\/\">alpha decay<\/a>,\u00a0<a href=\"https:\/\/www.radiation-dosimetry.org\/what-is-beta-decay-beta-radioactivity-definition\/\">beta decay<\/a>,\u00a0<a href=\"https:\/\/www.radiation-dosimetry.org\/what-is-gamma-decay-gamma-radioactivity-definition\/\">gamma decay<\/a>,\u00a0or\u00a0<a href=\"https:\/\/www.radiation-dosimetry.org\/what-is-electron-capture-inverse-beta-decay-definition\/\">electron capture<\/a>. Many other rare types of decay, such as <a href=\"https:\/\/www.radiation-dosimetry.org\/what-is-spontaneous-fission-definition\/\">spontaneous fission<\/a> or neutron emission, are known.<\/p>\n<h2>Mass of Atom<\/h2>\n<p>See also: <a href=\"https:\/\/material-properties.org\/atomic-mass-of-chemical-elements\/\">Atomic Masses<\/a><\/p>\n<p>Since <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-electron-properties-of-electron\/\">electrons<\/a> are almost massless (in comparison to the nucleons), the total number of <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-proton-properties-of-proton\/\">protons<\/a> and <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/\">neutrons<\/a> in the nucleus of an atom determines the atomic mass. The total number of protons and neutrons in the nucleus of an atom is called the <strong>atomic mass number<\/strong> (or the mass number) of the atom and is given the symbol <strong>A<\/strong>. The mass number is different for each different isotope of a chemical element. The <strong>mass number<\/strong> is written either after the element name or as a superscript to the left of an element\u2019s symbol. For example, the most common isotope of carbon is carbon-12 or <sup>12<\/sup>C.<\/p>\n<p>The unit of measure for mass is the <strong>atomic mass unit (amu)<\/strong>. One atomic mass unit is equal to 1.66 x 10<sup>-24<\/sup> grams.<\/p>\n<p>Besides the <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-mass-and-weight\/standard-kilogram\/\">standard kilogram<\/a>, it is a second mass standard. It is the carbon-12 atom, which, by international agreement, has been assigned a mass of 12 atomic mass units (u). The relation between the two units is<\/p>\n<p>One atomic mass unit is equal:<\/p>\n<p>1u = 1.66 x 10<sup>-24<\/sup> grams.<\/p>\n<p>One unified atomic mass unit is <strong>approximately<\/strong> the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g\/mol.<\/p>\n<p>For <sup>12<\/sup>C, the atomic mass is exactly 12u since the atomic mass unit is defined from it. The isotopic mass usually differs for other isotopes and is usually within 0.1 u of the mass number. For example, <strong><sup>63<\/sup><\/strong><strong>Cu<\/strong> (29 protons and 34 neutrons) has a mass number of 63, and an isotopic mass in its <strong>nuclear ground state is 62.91367 u.<\/strong><\/p>\n<p>There are two reasons for the difference between mass number and isotopic mass, known as the <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/nuclear-energy\/mass-defect\/\">mass defect<\/a>:<\/p>\n<ol>\n<li>The <strong>neutron is<\/strong> slightly<strong> heavier<\/strong> than the <strong>proton<\/strong>, increasing the mass of nuclei with more neutrons than protons relative to the atomic mass unit scale based on <sup>12<\/sup>C with equal numbers of protons and neutrons.<\/li>\n<li>The <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/binding-energy\/nuclear-binding-energy\/\">nuclear binding energy<\/a> varies between nuclei, and a nucleus with greater binding energy has lower total energy and a <strong>lower mass<\/strong> according to <a href=\"http:\/\/sitepourvtc.com\/laws-of-conservation\/law-of-conservation-of-energy\/conservation-of-mass-energy-mass-energy-equivalence\/\">Einstein\u2019s mass-energy equivalence<\/a> relation <em>E<\/em> = <em>mc<\/em><sup>2<\/sup>. For <strong><sup>63<\/sup><\/strong><strong>Cu,<\/strong> the atomic mass is less than 63, so this must be the dominant factor.<\/li>\n<\/ol>\n<h2>Ionization Energy of Atoms<\/h2>\n<p><strong>Ionization energy<\/strong>, also called<strong> ionization potential<\/strong>, is the energy necessary to<strong> remove an electron<\/strong> from the neutral atom.<\/p>\n<p>X + energy \u2192 X<sup>+<\/sup> + e<sup>\u2212<\/sup><\/p>\n<p>where X is any atom or molecule capable of ionizing, X<sup>+<\/sup> is that atom or molecule with an electron removed (positive ion), and e<sup>\u2212<\/sup> is the removed electron.<\/p>\n<p>There is ionization energy for each successive electron removed. The electrons that circle the nucleus move in fairly well-defined orbits, and some of these electrons are more tightly bound in the atom than others. For example, only 7.38 eV is required to remove the outermost electron from a lead atom, while 88,000 eV is required to remove the innermost electron.<\/p>\n<ul>\n<li><strong>Ionization energy<\/strong> is lowest for the alkali metals, which have a single electron outside a closed shell.<\/li>\n<li><strong>Ionization energy<\/strong> increases across a row on the periodic maximum for the noble gases which have closed shells.<\/li>\n<\/ul>\n<p>For example, sodium requires only 496 kJ\/mol or 5.14 eV\/atom to ionize it. On the other hand, neon, the noble gas immediately preceding it in the periodic table, requires 2081 kJ\/mol or 21.56 eV\/atom.<\/p>\n<p>The ionization energy associated with removing the first electron is most commonly used. The <em>n<\/em>th ionization energy refers to the amount of energy required to remove an electron from the species with a charge of (<em>n<\/em>-1).<\/p>\n<p>1st ionization energy<\/p>\n<p>X \u2192 X<sup>+<\/sup> + e<sup>\u2212<\/sup><\/p>\n<p>2nd ionization energy<\/p>\n<p>X<sup>+<\/sup> \u2192 X<sup>2+<\/sup> + e<sup>\u2212<\/sup><\/p>\n<p>3rd ionization energy<\/p>\n<p>X<sup>2+<\/sup> \u2192 X<sup>3+<\/sup> + e<sup>\u2212<\/sup><\/p>\n<p>For example, only 7.38 eV is required to remove the outermost electron from a lead atom, while 88,000 eV is required to remove the innermost electron.<\/p>\n<figure id=\"attachment_16766\" aria-describedby=\"caption-attachment-16766\" style=\"width: 1014px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Ionization-energy-first-min.png\"><img loading=\"lazy\" class=\"size-large wp-image-16766\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Ionization-energy-first-min-1024x388.png\" alt=\"Ionization energy\" width=\"1024\" height=\"388\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Ionization-energy-first-min-1024x388.png 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Ionization-energy-first-min-300x114.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Ionization-energy-first-min.png 1139w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-16766\" class=\"wp-caption-text\">Source: wikipedia.org License: CC BY-SA 3.0<\/figcaption><\/figure>\n<h2>Atomic Radius of Chemical Elements<\/h2>\n<p>It must be noted that atoms lack a well-defined outer boundary. The atomic radius of a chemical element measures the distance out to which the electron cloud extends from the nucleus. However, this assumes the atom exhibits a spherical shape, which is only obeyed for atoms in a vacuum or free space. Therefore, there are various non-equivalent definitions of atomic radius.<\/p>\n<ul>\n<li><strong>Van der Waals radius. <\/strong>In principle, Vana der Waals radius is half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule.<\/li>\n<li><strong>Ionic radius. <\/strong>An ionic radius is one-half the distance between the nuclei of two ions in an ionic bond.<\/li>\n<li><strong>Covalent radius. <\/strong>A covalent\u00a0radius is the nominal radius of the atoms of an element when covalently bound to other atoms.<\/li>\n<li><strong>Metallic radius. <\/strong>A metallic radius is one-half the distance between the nuclei of two adjacent atoms in a crystalline structure when joined to other atoms by metallic bonds.<\/li>\n<\/ul>\n<p>See also: <a href=\"https:\/\/material-properties.org\/atomic-radius-of-chemical-elements\/\">Atomic Radii<\/a><\/p>\n<h2>Volume of Atom<\/h2>\n<figure id=\"attachment_16479\" aria-describedby=\"caption-attachment-16479\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/01\/atomic-nucleus-volume-min.png\"><img loading=\"lazy\" class=\"size-medium wp-image-16479\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/01\/atomic-nucleus-volume-min-300x300.png\" alt=\"\" width=\"300\" height=\"300\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/01\/atomic-nucleus-volume-min-300x300.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/01\/atomic-nucleus-volume-min-150x150.png 150w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/01\/atomic-nucleus-volume-min-66x66.png 66w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/01\/atomic-nucleus-volume-min.png 591w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-16479\" class=\"wp-caption-text\">A figurative depiction of the helium-4 atom with the electron cloud in shades of gray. Protons and neutrons are most likely found in the same space, at the central point. Source wikipedia.org License CC BY-SA 3.0<\/figcaption><\/figure>\n<p><strong>The volume of an atom<\/strong>\u00a0is about\u00a0<strong>15 orders of magnitude<\/strong>\u00a0<strong>larger\u00a0<\/strong>than the volume of a nucleus. For\u00a0<strong>uranium atom<\/strong>, the\u00a0<strong>Van der Waals radius<\/strong>\u00a0is about\u00a0<strong>186 pm = 1.86 \u00d710<sup>\u221210<\/sup>m<\/strong>. The Van der Waals radius, r<sub>w<\/sub>, of an atom is the radius of an imaginary hard-sphere representing the distance of the closest approach to another atom. Assuming a spherical shape, the<a href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-fuel\/uranium\/\">\u00a0uranium\u00a0<\/a>atom has a volume of about \u00a0<strong>26.9 \u00d710<sup>\u221230<\/sup>\u00a0m<sup>3<\/sup><\/strong>. But this \u201chuge\u201d space is occupied primarily by electrons because the <b>nucleus <\/b>occupies\u00a0only about\u00a0<strong>1721\u00d710<sup>\u221245<\/sup>\u00a0m<sup>3<\/sup><\/strong> of space. Together, these electrons weigh only a fraction (let\u2019s say 0.05%) of the entire atom.<\/p>\n<p>It may seem that the space and the matter are <strong>empty<\/strong>,\u00a0<strong>but it is not<\/strong>. Due to the <strong>quantum nature of electrons<\/strong>, the electrons are not pointing particles, and they are smeared out over the whole atom. The classical description cannot be used to describe things on the atomic scale. On the atomic scale, physicists have found that quantum mechanics describes things very well on that scale. Particle locations in quantum mechanics are not at an exact position, and they are described by a <strong>probability density function<\/strong>. Therefore the space in an atom (between electrons and an atomic nucleus) is not empty. Still, it is filled by a probability density function of electrons (usually known as \u201c<strong>electron cloud \u201c<\/strong>).<\/p>\n<h2>Antiatom<\/h2>\n<p><strong>Antimatter<\/strong> refers to material that would be made up of \u201c<strong>antiatoms<\/strong>\u201d in which <strong>antiprotons<\/strong> and <strong>antineutrons<\/strong> would form the nucleus around which <strong>positrons<\/strong> (antielectrons) would move. The term is also used for antiparticles in general.<\/p>\n<p><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/10\/Antimatter-antihydrogen-atom-min.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-19957\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/10\/Antimatter-antihydrogen-atom-min-300x213.png\" alt=\"Antimatter - antihydrogen atom\" width=\"300\" height=\"213\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/10\/Antimatter-antihydrogen-atom-min-300x214.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/10\/Antimatter-antihydrogen-atom-min.png 1015w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>Antimatter<\/strong> particles bind with one another to form antimatter, just as ordinary particles bind to form normal matter. For example, a positron and an antiproton can form an antihydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible and anti-atoms corresponding to the known chemical elements.<\/p>\n<p>Our visible Universe is almost entirely composed of matter, and very little antimatter has existed since the Big Bang. This problem is known as the <strong>baryon asymmetry<\/strong>. This asymmetry of matter and antimatter in the visible Universe is one of the great unsolved problems in physics.<\/p>\n<p><strong>In the special theory of relativity,<\/strong> certain types of <strong>matter may be created or destroyed. <\/strong>Still, the mass and energy associated with such matter <strong>remain unchanged in quantity in all of these processes<\/strong>. As a result of the conservation of lepton and baryon numbers, \u00a0antimatter (antiparticles) can be created out of energy, but only if a particle counterpart for every antiparticle is created as well.<\/p>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-antimatter\/matter-antimatter-creation-and-annihilation\/\">Matter &#8211; Antimatter Creation and Annihilation<\/a><\/p>\n<\/div>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:20px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>References:<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>Nuclear and Reactor Physics:<\/strong>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n<li>J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n<li>W. M. Stacey, Nuclear Reactor Physics, John Wiley &amp; Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n<li>Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n<li>W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n<li>Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.<\/li>\n<li>U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.<\/li>\n<li>Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.<\/li>\n<\/ol>\n<p><strong><\/strong><strong>Advanced Reactor Physics:<\/strong><\/p>\n<ol>\n<li>K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n<li>K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n<li><span style=\"font-weight: 400;\">D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.\u00a0<\/span><\/li>\n<li>E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.<\/li>\n<\/ol>\n<\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Atomic Physics<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>The physical world is composed of combinations of various subatomic or fundamental particles. These are the smallest building blocks of matter. All matter except dark matter is made of molecules, which are themselves made of atoms. The atoms are the smallest constituents of ordinary matter, which can be divided without releasing electrically charged particles. The &#8230; <a title=\"What is Atom &#8211; Properties of Atoms\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/\" aria-label=\"More on What is Atom &#8211; Properties of Atoms\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":11224,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/23305"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=23305"}],"version-history":[{"count":9,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/23305\/revisions"}],"predecessor-version":[{"id":37669,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/23305\/revisions\/37669"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/11224"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=23305"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}