Hint 1 determine the number of neutrons for an

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Hint 1. Determine the number of neutrons for an example atom How many neutrons does -15 contain? Express your answer numerically as an integer. Hint 1. How to determine the number of neutrons In the isotope notation given here, -15, the number 15 represents the mass number of the isotope. The mass number is determined by the equation shown here: You can rearrange this equation to solve for the number of neutrons. Hint 2. How to determine the atomic number Each element has a unique atomic number, which is equal to the number of protons in the nucleus of an atom. The periodic table of elements is arranged by the atomic number of the elements. For a given element, look above the symbol in the periodic table to find the atomic number. For example, carbon has an atomic number of 6. ANSWER: Correct ANSWER: Correct Atomic Mass Calculations Atomic mass is a weighted average of the masses of the naturally occurring isotopes of that element. For example, consider isotopes of lithium: Isotope Abundance ( ) Mass ( ) 7.5 6.015 N N mass number = atomic number + number of neutrons 8 Help Reset The correct ranking cannot be determined. Fewest neutrons Most neutrons % amu Li 6 Li 7 Cl-37 S-36 Cl-35 S-34 S-33 S-32
92.5 7.016 The atomic mass is therefore Notice that the atomic mass is closer to 7 than it is to 6. That is because the heavier isotope is more abundant. Part A On a mission to a newly discovered planet, an astronaut finds chlorine abundances of 13.85 for and 86.15 for . What is the atomic mass of chlorine for this location? The mass of is 34.97 . The mass of is 36.97 . Express your answer in atomic mass units using four significant figures. Hint 1. Estimate the answer Based on the percent abundances, give an estimate of the atomic mass. ANSWER: Correct Li 7 (0.075 × 6.015) + (0.925 × 7.016) = 6.94 amu % Cl 35 % Cl 37 Cl 35 amu Cl 37 amu The atomic mass will be between 35 and 36 . equal to 36 . between 36 and 37 . amu amu amu
Correct Part B The astronaut then measures the abundance of silicon on the new planet, obtaining the following results: Isotope Abundance ( ) Mass ( ) 73.71 27.98 14.93 28.98 11.36 29.97 What is the atomic mass of silicon for this planet? Express your answer in atomic mass units using four significant figures. Hint 1. Estimate the answer Based on the percent abundances, give an estimate of the atomic mass. % amu Si 28 Si 29 Si 30 . .
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