Consider the following atoms in which X represents the chemical symbol of the element:168X 169X 1810X 178X 188Xc. Which atoms have the same mass number?

Ch.4 Atoms and Elements

Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 13th Edition

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Timberlake 13th Edition

Ch.4 Atoms and Elements

Problem 81c

Chapter 4, Problem 81c

Consider the following atoms in which X represents the chemical symbol of the element:
¹⁶₈X ¹⁶₉X ¹⁸₁₀X ¹⁷₈X ¹⁸₈X
c. Which atoms have the same mass number?

Verified step by step guidance

Step 1: Understand the concept of mass number. The mass number is the sum of protons and neutrons in the nucleus of an atom. It is represented as the superscript number before the chemical symbol (e.g., ¹¹⁵X).

Step 2: Analyze the given atoms. Each atom is represented with its mass number (superscript) and atomic number (subscript). For example, ¹¹⁵₄₉X has a mass number of 115 and an atomic number of 49.

Step 3: Compare the mass numbers of the given atoms. Look for atoms that have the same superscript value, as this indicates they have the same mass number.

Step 4: Identify the atoms with the same mass number. From the image, the atoms ¹¹⁵₄₉X, ¹¹⁵₄₆X, and ¹¹⁵₅₀X all have a mass number of 115.

Step 5: Conclude that the atoms with the same mass number are isotopes of different elements, as they have the same number of nucleons but different atomic numbers.

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Key Concepts

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

Mass Number

The mass number of an atom is the total number of protons and neutrons in its nucleus. It is represented as the upper left number in the atomic notation (e.g., ¹⁶ in ¹⁶₈X). Atoms with the same mass number have the same total number of nucleons, which can indicate they are isotopes of the same element.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different mass numbers. For example, the isotopes of element X in the question include ¹⁶₈X and ¹⁸₁₀X, which have different mass numbers but belong to the same element.

Atomic Number

The atomic number of an element is the number of protons in the nucleus of an atom, which determines the element's identity. It is represented as the lower left number in the atomic notation (e.g., ₈ in ¹⁶₈X). Atoms with the same atomic number are the same element, while differing atomic numbers indicate different elements.

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