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Mendeleev's Periodic Table — Reading Comprehension

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This passage explores Dmitri Mendeleev’s creation of the periodic table in 1869, a breakthrough that shaped the course of modern chemistry. Aligned to NGSS standard MS-PS1-1, it explains how Mendeleev organized elements by atomic mass, recognized repeating patterns in their properties, and left gaps for elements not yet discovered. The passage examines how his predictions of missing elements, such as gallium and germanium, were later confirmed, validating his scientific method. Students will learn about the cause-and-effect reasoning behind the table’s development, the interaction of scientific observation and theory, and the wider impact on science and society. Glossary terms, multiple-choice questions, writing prompts, and graphic organizers help reinforce understanding. The passage is also available in Spanish and differentiated versions for diverse learners. Audio integration supports accessibility. This resource is ideal for middle school science classrooms seeking engaging, standards-based materials on the history of science and the development of scientific models.

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Mendelejevs periodiska system 1871 — "Mendeleev's periodic table 1871" by The original uploader was Den fjättrade ankan at Swedish Wikipedia. / Wikimedia Commons (Public domain).

Chemical elements are the basic building blocks of all matter. In the mid-1800s, scientists struggled to organize the growing list of known elements in a meaningful way. The challenge was to find a system that grouped elements with similar properties together and revealed patterns in their behavior. The solution to this problem changed the study of chemistry forever.

In 1869, Russian chemist Dmitri Mendeleev created the first widely recognized periodic table. Mendeleev arranged the elements in order of increasing atomic mass, which is the total mass of protons and neutrons in an atom's nucleus. He noticed that elements with similar properties appeared at regular intervals, or periods. By placing elements into rows and columns, Mendeleev revealed a repeating pattern known as periodicity. This pattern showed that certain chemical and physical properties, such as reactivity or melting point, recurred in predictable ways.

Leaving Gaps and Making Predictions

Mendeleev's genius was not just in organizing known elements, but in leaving empty spaces where he believed undiscovered elements should fit. For example, he left a gap below aluminum and predicted the existence and properties of an element he called "eka-aluminum." Years later, the element gallium was discovered, matching Mendeleev's predictions almost exactly. He also predicted the element germanium, which was found about 15 years later. These successful predictions provided strong evidence that the periodic table was more than just a chart—it was a powerful scientific model. The accuracy of his forecasts convinced other scientists of the value of his system and encouraged further searches for unknown elements.

Scientific Principles and Impact

Mendeleev’s periodic table demonstrated the importance of organizing data to uncover patterns and make predictions. His work introduced the concept of periodic law, which states that the properties of elements are a periodic function of their atomic masses (today we use atomic numbers). This idea showed that the structure of matter is not random, but follows natural laws. The periodic table became a key tool for scientists, helping them understand chemical reactivity, make new materials, and develop technologies like batteries and medicines. Mendeleev’s approach of using patterns to predict the unknown is a central part of scientific thinking and discovery.

Continuing Developments

Although Mendeleev organized his table by atomic mass, we now arrange elements by atomic number, which is the number of protons in an atom. This change, made in the early 1900s, fixed some issues with the original table and made the pattern even clearer. Today, the periodic table includes over 100 elements and continues to grow as new elements are synthesized. Mendeleev’s method of predicting and testing ideas based on observed patterns still guides scientific research. The periodic table remains a symbol of how organizing information can reveal the hidden order of the natural world.

Interesting Fact: Element 101 was named mendelevium in honor of Dmitri Mendeleev’s contributions to science.

What was Mendeleev’s main achievement in 1869?

He created the first widely recognized periodic table.He discovered the element gallium.He invented atomic theory.He developed the atomic bomb.

How did Mendeleev arrange the elements in his periodic table?

By alphabetical orderBy atomic massBy atomic numberBy color

Which of the following is an example of a property mentioned in the passage?

ShapeReactivitySizeTaste

What does the term 'periodicity' mean in the context of the periodic table?

The continuous increase in atomic sizeA repeating pattern of properties among elementsThe random order of elementsGrouping elements by color

What is the significance of the gaps Mendeleev left in his periodic table?

They showed where undiscovered elements would fit.They made the table look neat.They represented missing data.They were mistakes in his work.

What scientific principle did Mendeleev’s periodic table help demonstrate?

Atomic theoryPeriodic lawEvolutionGravity

Why was the discovery of gallium and germanium important for Mendeleev’s table?

They were new metals for industry.They matched his predictions, proving his model’s accuracy.They were used in batteries.They proved atomic mass was not important.

How is the modern periodic table different from Mendeleev’s original version?

It is organized by atomic number, not atomic mass.It uses more colors.It only includes metals.It has fewer elements.

True or False: Mendeleev’s periodic table helped scientists predict the properties of undiscovered elements.

TrueFalse

True or False: The periodic table is no longer useful for scientists today.

TrueFalse