Ch.2 - Atoms, Molecules, and Ions

Problem 31b,c

Chapter 2, Problem 31b,c

Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements in the front inside cover as needed: (b) the isotope of krypton with mass number 84 (c) the isotope of rhenium with mass number 187

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Identify the element symbol for krypton, which is 'Kr'.

Understand that the mass number is the total number of protons and neutrons in the nucleus of an atom.

The mass number is given as 84, which will be the superscript to the left of the element symbol.

Determine the atomic number of krypton, which is the number of protons. Krypton has an atomic number of 36.

Write the isotope notation with the mass number as the superscript and the atomic number as the subscript: \( ^{84}_{36} \text{Kr} \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This difference in neutron count results in varying mass numbers for the isotopes. For example, krypton (Kr) has several isotopes, and the mass number indicates the total number of protons and neutrons in the nucleus.

Nuclear Notation

Nuclear notation is a way of representing isotopes using the element's symbol, with the mass number as a superscript and the atomic number as a subscript. The atomic number indicates the number of protons, while the mass number represents the total number of protons and neutrons. For krypton with a mass number of 84, the notation would be written as 84Kr.

Element Symbols

Element symbols are one- or two-letter abbreviations used to represent chemical elements on the periodic table. Each element has a unique symbol, often derived from its English or Latin name. For krypton, the symbol is 'Kr', which is essential for correctly writing its nuclear notation when identifying isotopes.

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Related Practice

Textbook Question

Fill in the gaps in the following table, assuming each column represents a neutral atom.

Symbol ¹¹²Cd

Protons 38 92

Neutrons 58 49

Electrons 38 36

Mass no. 81 235

Complete the second row of the table.

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Textbook Question

Fill in the gaps in the following table, assuming each column represents a neutral atom.

Symbol ¹¹²Cd

Protons 38 92

Neutrons 58 49

Electrons 38 36

Mass no. 81 235

Complete the third row of the table.

Complete the fourth row of the table.

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Textbook Question

Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements in the front inside cover as needed: (a) the isotope of platinum that contains 118 neutrons

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Textbook Question

Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements in the front inside cover as needed: (d) the isotope of magnesium that has an equal number of protons and neutrons.

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Textbook Question

The atomic weight of boron is reported as 10.81, yet no atom of boron has the mass of 10.81 amu. Which is the best explanation?

a. The measurement of atomic mass is only reliable to two significant figures.

b. The atomic weight is an average of many individual atoms.

c. The atomic weight is an average of many isotopes of the same nuclear composition.

Textbook Question

(b) Why is the atomic weight of carbon reported as 12.011 in the table of elements and the periodic table in the front inside cover of this text?

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