1. Atomic structure
A section of Chemistry, 9701
Listing 10 of 359 questions
Sulfur, S, and polonium, Po, are both elements in Group VI of the Periodic Table. Sulfur has three isotopes. Explain the meaning of the term isotope. A sample of sulfur has the following isotopic composition by mass. isotope mass % by mass 95.00 0.77 4.23 Calculate the relative atomic mass, Ar, of sulfur to two decimal places. Ar = Isotopes of polonium, proton number 84, are produced by the radioactive decay of several elements including thorium, Th, proton number 90. The isotope 213Po is produced from the thorium isotope 232Th. Complete the table below to show the atomic structures of the isotopes 213Po and 232Th. number of isotope protons neutrons electrons 213Po 232Th Radiochemical reactions, such as nuclear fission and radioactive decay of isotopes, can be represented by equations in which the nucleon numbers must balance and the proton numbers must also balance. For example, the nuclear fission of uranium-235, 235 92U, by collision with a neutron, 1 0n, produces strontium-90, xenon-143 and three neutrons. 92U + 1 0n 38Sr + 143 54Xe + 3 0n In this equation, the nucleon numbers balance because: 235 + 1 = 90 + 143 + (3x1). The proton numbers also balance because: 92 + 0 = 38 + 54 + (3x0). In the first stage of the radioactive decay of 90 Th, the products are an isotope of element E and an alpha-particle, 4 2 He. By considering nucleon and proton numbers only, construct a balanced equation for the formation of the isotope of E in this reaction. 90Th + 4 2 He Show clearly the nucleon number and proton number of the isotope of E. nucleon number of the isotope of E proton number of the isotope of E Hence state the symbol of the element E.
9701_w11_qp_23
THEORY
2011
Paper 2, Variant 3
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