Problem: Silicon (Si) has three isotopes: 28Si, 29Si, and 30Si. Determine the number of p+, no, and e ñ in each isotope.
Plan: mass number = the sum of protons and neutrons. Find (inside textís front cover) the atomic number (Z), which equals both the number of protons and the number of electrons. A minus Z gives the number of neutrons . Solution: The atomic number of silicon is 14. Therefore, 28Si has 14 p+ , 14 eñ , and 14 no (28 - 14).
29Si has 14 p+ , 14 eñ , and 15 no (29 - 14).
30Si has 14 p+ , 14 eñ , and 16 no (30 - 14).
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Skill 2. Using atomic notation to express the subatomic makeup of an isotope
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