Nuclear Chemistry Aim Nuke 2 – What is Radioactivity? Watch the video below for extra understanding!

Nuclear Chemistry the subfield of chemistry dealing with: radioactivity, nuclear processes, and nuclear properties. Radioactivity is based on an atom’s nuclear stability The Strong Nuclear Force (SNF) - A fundamental force that holds nucleons together Binding Energy – the “strength” of the SNF Nucleons – particles in the nucleus (protons and neutrons)

Stable nuclei When the SNF holds the nucleons together There is no break down of the nucleus Unstable nuclei or radioisotopes When the SNF cannot hold the nucleons together the nucleus breaks down or decays This results in the nucleus emitting (releasing) nuclear radiation Nuclear Radiation particles or waves of energy See Table O at right)

Unstable nuclei are due to: The ratio of protons to neutrons affects stability As nuclei increase in size A 1:1 ratio of protons to neutrons does NOT make the nucleus stable In general, for elements 1 to 83, there is at least one stable nucleus Above 83, there are only radioisotopes for each element Radioisotopes - Isotopes that are unstable due to the particular ratio of protons to neutrons

Radioactivity or Radiation The breakdown of nuclei emits different types of radiation The four main forms of decay in this class, from least penetrating to most penetrating: Alpha decay – a helium nucleus is emitted Beta decay – a high energy electron is emitted Positron decay – a positron (an anti-matter electron) is emitted Gamma decay – gamma rays (high energy electromagnetic waves) are emitted

Dangers of Radioactivity Each radiation has its own factors making it dangerous Alpha particles (helium nuclei) have a +2 charge that ionizes materials (Ionizing radiation – can alter DNA!) Beta particles are small but can ionize (a -1 charge) deep into materials a high energy electron is emitted Positrons are the same as beta, but a +1 charge Gamma rays do not have a charge, but are the most dangerous as they put large amounts of energy into tissue Radioactive particles can be separated by charged plates Why don’t gamma rays move toward a positive or negative plate? Which plate would positrons move toward?

Dangers of Radioactivity Gamma rays are similar to X-rays and can destroy tissue Shorter the wavelength on the EM Spectrum The more energy there is in the rays Think about what ultraviolet light does to you on a sunny day at the beach!

Decay modes Elements each decay and release different radiations Table N – gives the decay modes, the half life of each radioisotope, and its name Half life - the TIME it takes for HALF of the radioisotope to decay Half lives are different for different isotopes They do not change with temperature, pressure, or any other variable

Natural Transmutation the spontaneous disintegration (breakdown) of an atom’s nucleus Natural transmutation When a nucleus disintegrates on its own one element changes to another without the addition of other particles Radioactive particles (alpha, beta, or positrons) or photons of energy (gamma rays) can also be released

Decay Series Radioactive elements will decay until they become a stable atom Most above atomic #83 will decay into lead (atomic # 82) Each element decays and changes into a new element based on what changes the decay does to the nucleus

Decay Series Alpha decay - releases a helium nucleus the original nucleus loses 2 p + and 2 n o Example 238 U  234 Th + 4 He Beta decay – a neutron in the nucleus decays into a proton and an electron The proton stays in the nucleus, but increases the atomic # by 1 The electron is emitted as a beta particle Example 234 Th  234 Pa + 0 e

Decay Series - releases a helium nucleus the original nucleus loses 2 p + and 2 n o Example: 238 U  234 Th + 4 He Positron decay – a proton in the nucleus decays into a neutron and a positron, an anti-matter electron The neutron stays in the nucleus but the loss of a proton lowers the atomic # by 1 The positron is emitted Example: 19 Ne  19 F + 0 e