Isotopes — Reading Comprehension

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MS-PS1-1

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This middle school science passage explores the concept of isotopes, which are atoms of the same element with different numbers of neutrons. Aligned to NGSS standard MS-PS1-1, the text defines isotopes, explains how differences in neutron numbers affect atomic mass, and illustrates these ideas with examples such as carbon-12, carbon-14, and the hydrogen isotopes protium, deuterium, and tritium. Students will learn how isotopes are used in real-world applications like carbon dating and medical imaging, and how scientists use evidence to understand atomic structure. The resource features a main passage, a differentiated version for struggling readers, Spanish translations, glossary, comprehension quiz, writing prompts, and graphic organizers. Audio integration supports diverse learners. This lesson builds foundational knowledge of atomic structure and connects to broader scientific principles, preparing students for deeper study in chemistry and the physical sciences.

CONTENT PREVIEW

The discovery that atoms of the same element can have different masses changed how scientists understood matter. An atom is made of three main parts: protons, neutrons, and electrons. All atoms of an element have the same number of protons, which defines the element. However, some atoms of the same element have different numbers of neutrons. These are called isotopes. Isotopes of an element share the same chemical properties but can have different physical properties because of their mass.

Atomic Structure and Isotopes
Isotopes exist because the number of neutrons in an atom can vary without changing the element's identity. For example, all carbon atoms have six protons, but carbon-12 has six neutrons, while carbon-14 has eight neutrons. Both are isotopes of carbon. The difference in neutron number causes a difference in atomic mass, which is the total number of protons and neutrons in an atom. The atomic mass listed on the periodic table is a weighted average of all the naturally occurring isotopes of an element, based on how common each isotope is. For carbon, about 98.9% of all atoms are carbon-12, so the average atomic mass is close to 12 atomic mass units (amu).

Examples of Isotopes and Their Uses
Isotopes are not just interesting for their structure—they are useful in science and technology. Carbon-14, for example, is used in carbon dating to estimate the age of ancient fossils and artifacts. Because carbon-14 is unstable and slowly decays over thousands of years, scientists can measure how much remains in a sample to calculate its age. Another example is hydrogen, which has three isotopes: protium (one proton, no neutrons), deuterium (one proton, one neutron), and tritium (one proton, two neutrons). Deuterium is used in research and nuclear reactors, while tritium is used in medical imaging and glow-in-the-dark devices.

Interactions, Applications, and Broader Connections
Understanding isotopes helps scientists solve problems in many fields. In medicine, certain isotopes are used as tracers to follow chemical reactions inside the body. In environmental science, isotopes help track sources of pollution or understand climate change by analyzing ice cores. The study of isotopes also supports larger scientific ideas, such as the law of conservation of mass and the structure of matter. By analyzing isotopes, scientists gain clues about processes that happened millions of years ago and about the workings of atoms today.

In summary, isotopes show that atoms of the same element can have different masses without changing their chemical identity. This discovery has led to important advances in science, technology, and our understanding of the universe.

Interesting Fact: Some isotopes are stable, while others are radioactive, meaning they break down over time and release energy—a process that powers nuclear reactors and helps date ancient objects!

What defines the identity of an element?

The number of protons in its atomsThe number of neutrons in its atomsThe total mass of its atomsThe number of electrons in its atoms

What is an isotope?

An atom with a different number of protonsAn atom with a different number of neutronsAn atom with more electrons than protonsAn atom with no nucleus

How is the atomic mass of an element on the periodic table determined?

It is the mass of the most common isotope only.It is the sum of all proton numbers for the element.It is a weighted average of all naturally occurring isotopes.It is the total number of elements in nature.

In the passage, what is one use of carbon-14?

Making glow-in-the-dark devicesEstimating the age of ancient objectsProducing food energyPowering nuclear reactors

What does the word 'tracers' mean as used in the passage?

Atoms that are very largeIsotopes used to follow chemical reactionsAtoms with no neutronsAtoms that decay quickly

What does 'weighted average' mean in this context?

An average that counts only the largest isotopeAn average that considers how common each isotope isAn average with no math involvedThe same as the most massive isotope

Why do isotopes of an element have different physical properties?

Because they have a different number of neutrons, changing their massBecause they have different numbers of protonsBecause they have different numbers of electronsBecause they are different elements

If a scientist finds a sample mostly containing carbon-12, what does this mean?

Carbon-12 is the most common isotope of carbonCarbon-14 is the most common isotope of carbonThe sample is not made of carbonThe atomic mass is more than 14 amu

True or False: All isotopes of an element have the same number of protons.

TrueFalse

True or False: Deuterium and tritium are both isotopes of hydrogen.

TrueFalse