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General Chemistry Principles, Patterns, and Applications, 2011

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The mass of an atom is a weighted average that is largely determined by the number of<br />

its protons <strong>and</strong> neutrons, whereas the number of protons <strong>and</strong> electrons determines its<br />

charge.<br />

C O N C E PTUAL P R OBLEMS<br />

1. Complete the following table for the missing elements, symbols, <strong>and</strong> numbers of electrons.<br />

Element Symbol Number of Electrons<br />

molybdenum<br />

19<br />

titanium<br />

B<br />

53<br />

Sm<br />

helium<br />

14<br />

2. Complete the following table for the missing elements, symbols, <strong>and</strong> numbers of electrons.<br />

Element Symbol Number of Electrons<br />

lanthanum<br />

Go<br />

aluminum<br />

80<br />

sodium<br />

One<br />

9<br />

Be<br />

3. Is the mass of an ion the same as the mass of its parent atom? Explain your answer.<br />

4. What isotopic st<strong>and</strong>ard is used for determining the mass of an atom?<br />

1. Give the symbol XZA for these elements, all of which exist as a single isotope.<br />

a. beryllium<br />

b. ruthenium<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

58

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