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Chapter 2: Q2.4CYL (page 84)
A sample of magnesium is found to contain 78.70% of 24Mg atoms (mass 23.98 amu), 10.13% of 25Mg atoms (mass 24.99 amu), and 11.17% of 26Mg atoms (mass 25.98 amu). Calculate the average mass of a Mg atom.
24.31 amu
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Write the empirical formula for the following compounds:
Using the periodic table, identify the heaviest member of each of the following groups:
(a) Alkali metals
(b) Chalcogens
(c) Noble gases
(d) Alkaline earth metals
Explain why the symbol for an atom of the element oxygen and the formula for a molecule of oxygen differ.
Click on the site (http://openstaxcollege.org/l/16PhetAtomMass) and select the 鈥淢ix Isotopes鈥� tab, hide the 鈥淧ercent Composition鈥� and 鈥淎verage Atomic Mass鈥� boxes, and then select the element boron.
(a) Write the symbols of the isotopes of boron that are shown as naturally occurring in significant amounts.
(b) Predict the relative amounts (percentages) of these boron isotopes found in nature. Explain the reasoning behind your choice.
(c) Add isotopes to the black box to make a mixture that matches your prediction in (b). You may drag isotopes fromtheir bins or click on 鈥淢ore鈥� and then move the sliders to the appropriate amounts.
(d) Reveal the 鈥淧ercent Composition鈥� and 鈥淎verage Atomic Mass鈥� boxes. How well does your mixture match withyour prediction? If necessary, adjust the isotope amounts to match your prediction.
(e) Select 鈥淣ature鈥檚鈥� mix of isotopes and compare it to your prediction. How well does your prediction comparewith the naturally occurring mixture? Explain. If necessary, adjust your amounts to make them match 鈥淣ature鈥檚鈥漚mounts as closely as possible.
Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.
(a) the alkali metal with 11 protons and a mass number of 23
(b) the noble gas element with 75 neutrons in its nucleus and 54 electrons in the neutral atom
(c) the isotope with 33 protons and 40 neutrons in its nucleus
(d) the alkaline earth metal with 88 electrons and 138 neutrons
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