Sciences - Co-ordinated (Double) - 0654 CIE

Isotopes

Overview

You might expect every atom of an element to be identical, but many elements come in slightly different versions. These versions, called isotopes, have the same chemistry but different masses. Chlorine, for example, is a blend of two isotopes, which is why its relative atomic mass is not a whole number.

In this lesson you will learn exactly what an isotope is, why isotopes of an element behave identically in chemical reactions, and how their existence explains the average masses you see in the Periodic Table.

Objectives

Define isotopes as different atoms of the same element that have the same number of protons but different numbers of neutrons.
Interpret and use symbols for atoms, e.g. ¹²₆C, and ions, e.g. ³⁵₁₇Cl⁻.
[Supplement] State that isotopes of the same element have the same chemical properties because they have the same number of electrons and therefore the same electronic configuration.
[Supplement] Calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes.

Lesson Note

Isotopes explain why relative atomic masses are often not whole numbers, and they are the reason a single element can have atoms of different mass. The idea also underpins radioactive dating, medical scans and a great deal of modern science.

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Lesson Evaluation

Congratulations on completing the lesson on Isotopes. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

Isotopes of an element have the same number of: A. Neutrons B. Protons C. Nucleons D. Mass numbers Answer: B
Isotopes of an element differ in their number of: A. Protons B. Electrons C. Neutrons D. Shells Answer: C
Why do isotopes of an element react in the same way? A. They have the same number of neutrons B. They have the same electron arrangement C. They have the same mass D. They are radioactive Answer: B
How many neutrons are in an atom of chlorine-37? (proton number 17) A. 17 B. 18 C. 20 D. 37 Answer: C
Why is the relative atomic mass of chlorine 35.5 and not a whole number? A. Chlorine has half a neutron B. It is an average of its isotopes C. Chlorine has no isotopes D. The protons vary Answer: B