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Nuclear Decay SPH3U Ms. Kueh Recall: What is the general structure of an atom? What determines the identity of an element? Standard Atomic Notation: 16 8π π΄ ππ π΄ = Atomic mass = π + π π = Atomic number = π π = symbol of element Chemical Reaction - the interaction of substances to form new substances word equation: carbon + oxygen -> carbon dioxide + energy chemical equation: In a chemical reaction the elements involved do not change. All elements present in the reactants are present in the products. Isotopes All oxygen atoms have _________________ protons. Most oxygen atoms have _________________ neutrons. ______________________ - atoms of the same element that have different numbers of neutrons. 1 1π» 2 1π» 3 1π» Protium Deuterium Tritium http://atomic.lindahall.org/what-is-an-isotope.html Forces in the atom Electrostatic Force - the force of __________________ or _________________ due to electric charges Strong Nuclear Force - attraction between nucleons (particles that make up the nucleus) - helps hold together the neutrons and protons in the nucleus of an atom Radioactive Decay Key idea - some isotopes are instable. For each element, there is an ideal ratio of π: π. Transmutation β changing one element to another or one isotope to another Radioactivity (Radioactive decay) - a process by which the nucleus of an atom spontaneously disintegrates and forms different atoms Nuclear Reactions β involves a change of nuclei of atoms, sometimes resulting in completely new elements There are 3 different types of radioactive decay: Alpha Decay - a helium nucleus consisting of two protons and two neutrons (called an β particle), is spontaneously emitted from the nucleus An atom of plutonium-240 decays into uranium-236, and a helium-4 nucleus. When a substance undergoes alpha decay, the mass number (A) is reduced by four and the atomic number (Z) is reduced by two. In a nuclear reaction the parent atom (X) is the reactant atom, and the daughter atom (Y) is the product atom Example 1 When Lead-204 undergoes alpha decay, it produces a stable Isotope. Determine the element and its atomic number and mass number. Write the nuclear reaction equation for this alpha decay. Beta Decay - reaction that involves the emission or capture of an electron or a positron (called beta particles) positron - particle similar to an electron except that is has a positive charge instead of a negative charge There are 3 main types of beta decay: Beta Negative Decay - an electron is emitted from the nucleus of a parent atom When a nucleus contains too many neutrons, the strong nuclear force becomes stronger than the electrostatic force. To maintain stability, a neutron spontaneously decays into a proton and an electron, and the electron is ejected from the nucleus. The equation for this reaction is: 3 3 0 1π» β 2π»π + β1π π΄ ππ β π΄ π+1π + β10π Beta Positive Decay - a proton changes into a neutron and a positron (symbolized by +10π) 11 6πΆ π΄ ππ β β 11 5π΅ + +10π π΄ πβ1π + +10π Electron Capture - this is where an electron is absorbed by a nucleus and combines with a proton to form a neutron. 56 28ππ π΄ ππ + β10π β + β10π β 56 27πΆπ π΄ πβ1π Example 2 When bismuth-214 undergoes beta-negative decay, it produces a stable isotope. Determine the element and its atomic number and mass number. Write the nuclear reaction equation for this beta decay. Gamma Decay - after a nuclear reaction such as alpha or beta decay has occurred, the daughter nucleus is in high-energy, or excited state. As a result the nucleus spontaneously releases energy in the form of a gamma ray to return to a lower more stable energy state. gamma ray - a highly energetic form of electromagnetic radiation that is emitted as a photon π΄ β ππ β π΄ππ + 00πΎ 3 β 2π»π β 32π»π + 00πΎ The * means the nucleus is in an excited state. Example 3 When dysprosium-152 undergoes gamma decay, its nucleus changes from an excited state to a stable state. Write the nuclear reaction equation for this gamma decay. Characteristics of Radioactive Decay Alpha particles, beta particles and gamma rays all pose a danger to living tissue because they can ionize, or strip the electrons from, atoms. Types of radiation that can ionize atoms are known as ionization radiation. When this makes contact with living tissue, it can result in burns, tumours and other harmful effects. It is important to protect tissues from exposure to ionizing radiation. Alpha particles have a strong ionizing ability due to their positive charge and relatively high mass but they travel a short distance before becoming absorbed making their danger minimal. Gamma rays and Beta particles have a greater penetrating range in air and must be shielded against. Homework: Pg 322 #3, 5, 6 Pg 329 #1 β 3, 5