Chemistry unit 5 of mastering chemistry
Chemistry unit 5 of mastering chemistry Chem 113.01
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This 4 page Class Notes was uploaded by Annika Verburg on Saturday October 1, 2016. The Class Notes belongs to Chem 113.01 at Abilene Christian University taught by Dr. Aaron Robinson in Fall 2016. Since its upload, it has received 2 views. For similar materials see Introductory Chemistry in Chemistry at Abilene Christian University.
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Date Created: 10/01/16
Chapter 5-Nuclear Chemistry Natural Radioactivity Radiation and radioisotopes o Elements H through Ca have stable nuclei o Above atomic number 20, most elements have isotopes (atoms with different number of neutrons) which are unstable The nuclear forces are not enough to overcome repulsion between protons (+) To relieve this “pressure” these isotopes, called radioisotopes, emit energy in the form of radiation o Radioisotopes are identified by writing the element name (or symbol) and the mass number of the isotope Ex: iodine has a radioisotope of mass umber 131. It is called iodine-131 or I-131 o Types of radiation: Alpha particles, beta particles, positrons, and gamma rays One form of relieving unstable nuclear “pressure” is to emit what is called an alpha particle from the nucleus An alpha particle has 2 protons and 2 neutrons- essentially the nucleus of a helium atom Because there are no electrons in this particle, it has a charge of +2 (two protons) The symbol for an alpha particle is the Greek letter alpha Alpha particles are the heaviest type of radiation (mass number of 41) An atom o Another form of radiation is called a beta particle Beta particles are essentially electrons with very high energy They have a charge of -1 and a mass like an electron (very small, so we say mass of 0) The symbol for a beta particle is the Greek letter beta or else the symbol When a beta particle is emitted, it is the result of a neutron being converted to a proton in the nucleus An atom that emits a beta particle does not change its mass (no change in mass number) but does not increase its atomic number by 1: it is therefore a new element o A third form of radiation is called a positron Positrons are electrons with +1 charge (not a proton- they are still much, much smaller than protons) They have the symbol When a positron is emitted, it is the result of a proton being converted to a neutron When an atom emits a positron, it does not change its mass, but it does reduce its atomic number by 1: it is a new element Biological effects of radiation o High energy particles (radiation) can collide with other atoms and result in loss of electrons- formation of charged ions which are not stable o This is where the term ionizing radiation comes from o Cells that divide rapidly are most susceptible to ionizing radiation: bone marrow cells, skin cells, fetal cells, cancer cells Protection from ionizing radiation o Smaller forms of radiation travel faster and farther then larger forms For speed/penetration: gamma rays > beta particles > alpha particles o Shielding oneself is required for protection from ionizing radiation- the air or even your skin will block alpha particles, heavy lab coats and gloves can block the beta particles, and gamma rays must be shielded with lead or concrete Nuclear Reactions Writing nuclear equations to show radioactive decay o When an atom undergoes radioactive decay and emits radiation, we can describe this process with an equation called a nuclear equation: As we expect with an equation, both sides must be equal o Mass number on left – sum of mass numbers on right o Atomic number on left – sum of atomic numbers on right Nuclear equations showing alpha decay: o Remember with alpha decay, the nucleus loses 2 protons (atomic number decreases by 2) and the mass number decreases by 4 o This is because an alpha particle is emitted o Recall the notation: Nuclear equations showing beta decay o Remember, for beta decay, the nucleus loses no mass number unchanged) but a neutron is converted into a proton (atomic number increases by 1) o Again, balance the atomic number a mass number in the reaction (using the symbol for beta decay aids in this process) Nuclear equations showing positron emission o Remember, for positron emission, the nucleus loses no mass, but in the process for emitting a positron, one proton is converted to a neutron (the atomic number decreases by 1) o This can be remembered by the symbol for a positron Nuclear equations showing gamma ray emission o Gamma rays no charge or mass- they are energy only o Balancing these equations involves differentiating a metastable nucleus (shown by the superscript “m”) before emitting energy and the stable nucleus (without the superscript “m”) after emitting gamma rays. Producing radioisotopes o Radioisotopes can be produced from stable atoms by bombarding them with particles These particles can be protons They can be neutrons Or they can by alpha particles o As with other nuclear equations, we must balance the atomic number on each side of the equations and the mass number on each side Radiation Measurement The amount of radiation can be measured in several ways, with several units o In terms of radiation ‘events’ (called disintegrations) the units are 10 The curie (Ci) which is 3.7 x 10 disintigrations/ second and The becquered (Bq) which is 1 disintigration/ second o In terms of radiation absorbed by a gram of material (like body tissue) or “absorbed dose” the units are The rad (radiation absorbed dose) or The gray (Gy) which is joules of energy absorbed by 1 kg of body tissue o In terms of the effective biological damage a type of radiation causes, the units are in either The rem (radiation equivalent in humans) or The Sievert (Sv) These units must be multiplied by a factor, depending on the type of radiation Half-life of a radioisotope Half-life refers to the amount of time it takes for ½ of a radioisotope sample to decay o It is measured in units of time (could be seconds, days, years, etc- depending on the stability of the radioisotope) Chapter 6- Ionic and molecular compounds Ions: Transfer of electrons
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