Ch.2 - Atoms, Molecules, and Ions

Problem 31d

Chapter 2, Problem 31d

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.

Verified step by step guidance

insert step 1> Identify the atomic number of magnesium from the periodic table, which is 12. This means magnesium has 12 protons.

insert step 2> Since the problem states that the isotope has an equal number of protons and neutrons, the number of neutrons is also 12.

insert step 3> Calculate the mass number of the isotope by adding the number of protons and neutrons: Mass number = 12 (protons) + 12 (neutrons) = 24.

insert step 4> Write the isotope symbol for magnesium, which includes the element symbol (Mg), the mass number as a superscript, and the atomic number as a subscript.

insert step 5> The correct isotope symbol for magnesium with equal protons and neutrons is \(^{24}_{12}\text{Mg}\).

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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 chemical element that have the same number of protons but different numbers of neutrons. This means they share the same atomic number but have different atomic masses. For example, magnesium has several isotopes, including magnesium-24, which has 12 protons and 12 neutrons.

Atomic Notation

Atomic notation is a way to represent elements and their isotopes using symbols that include the element's chemical symbol, the atomic number (number of protons), and the mass number (total number of protons and neutrons). The mass number is written as a superscript and the atomic number as a subscript. For magnesium-24, it is represented as ²⁴₁₂Mg.

Protons and Neutrons

Protons and neutrons are subatomic particles found in the nucleus of an atom. Protons carry a positive charge and determine the element's identity, while neutrons are neutral and contribute to the atomic mass. The number of protons defines the atomic number, and in isotopes, the number of neutrons can vary, affecting the stability and properties of the element.

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Neutron-to-Proton Plot

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 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: (b) the isotope of krypton with mass number 84 (c) the isotope of rhenium with mass number 187

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Textbook Question

Without doing any detailed calculations (but using a periodic table to give atomic weights), rank the following samples in order of increasing numbers of atoms: 0.2 mol PCl5 molecules, 80 g Fe2O3, 3.0 3 1023 CO molecules.

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Textbook Question

(a) What isotope is used as the standard in establishing the atomic mass scale?

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Textbook Question

(b) The atomic weight of boron is reported as 10.81, yet no atom of boron has the mass of 10.81 u. Explain.