Element Q has three naturally occurring isotopes

CHEMISTRY · Multi-part · A Level · Chemistry · Atomic structure · Atomic structure

Problem

Element Q has three naturally occurring isotopes. Two of them are already well characterized: • Isotope Q-24: mass number 24.00 u, natural abundance 78.99\% • Isotope Q-25: mass number 25.00 u, natural abundance 10.00\% A newly discovered third isotope, Q-x, completes the natural sample. Precise measurements give the average atomic mass of element Q as 24.31 u. Using the data above, answer the following questions. Show all algebraic steps and justify your reasoning. (a) Let AxA_x represent the mass number of isotope Q-x and pxp_x represent its percent natural abundance. Write an explicit algebraic expression for the average atomic mass of element Q in terms of AxA_x and pxp_x. (b) Using the given average atomic mass, solve for pxp_x in terms of AxA_x. (c) Experiments indicate that isotope Q-x contains 13 neutrons. Determine (i) its mass number AxA_x and (ii) its percent natural abundance pxp_x. (d) Write the complete nuclear symbol for isotope Q-x, including atomic number, mass number, and chemical symbol. Explain each component of the symbol.

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