Elements

Elements

Middle School

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Learning Objectives

• Define an element as a pure substance made of only one type of atom.

• Describe how to identify substances using their unique physical and chemical properties.

• Explain how the periodic table organizes elements by their structure and properties.

• Recognize that elements combine to form all matter in the universe.

Key Vocabulary

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Element

A pure substance that cannot be broken down into simpler substances by any chemical means.

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Atom

The basic and smallest unit of a chemical element that can exist on its own.

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Substance

A form of matter that has a consistent chemical composition and characteristic properties throughout it.

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Physical Property

A characteristic of a substance that can be observed or measured without changing its identity.

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Chemical Property

A characteristic that is observed during a reaction in which the substance's identity is changed.

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Periodic Table

A chart that systematically organizes all known chemical elements based on their atomic number and properties.

Key Vocabulary

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Group

A group is a column on the periodic table where all the elements have similar properties.

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Electrolysis

Electrolysis is the process of using electricity to break down and separate different chemical substances.

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Radioactivity

This is the emission of radiation that comes from the unstable nucleus of an atom.

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What Is an Element?

Ancient Ideas

• Ancient cultures believed everything was made from four elements: air, fire, earth, and water.

• They thought properties like hot, cold, wet, and dry combined to create all substances.

• This understanding was based on philosophy and observation rather than controlled experiments.

Modern Science

• An element is a pure substance that cannot be broken down into simpler substances.

• Chemists used experiments with heat and electricity to discover the true nature of elements.

• Elements like iron, carbon, and oxygen are the basic building blocks of all matter.

Multiple Choice

What is the modern scientific definition of an element?

• A pure substance that cannot be broken down into simpler substances

• A combination of air, fire, earth, and water

• A substance created through philosophy and observation

• A material that is either hot, cold, wet, or dry

Multiple Choice

What is the main difference between how ancient cultures and modern scientists developed their ideas about elements?

• Modern science uses experiments, while ancient ideas were based on observation.

• Modern science focuses on four main elements, while ancient ideas had many.

• Ancient ideas used heat and electricity, while modern science uses philosophy.

• Ancient ideas were about building blocks, while modern science is about properties.

Multiple Choice

A scientist uses electricity to break down a sample of water, and finds it is made of oxygen and hydrogen. What does this experiment suggest about water?

• Water is not an element because it can be broken down into simpler substances.

• Water is one of the four ancient elements because it is wet.

• Water is an element because it is a pure substance found in nature.

• Water is an element because it was tested with electricity.

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Atoms: The Building Blocks of Elements

What is an Atom?

• An atom is the smallest possible unit of an element.

• It retains all of the chemical properties of that element.

• For example, a single gold atom is the smallest unit of gold.

What is an Element?

• An element is a substance made of only one type of atom.

• A sample of pure iron contains only iron atoms.

• The differences between elements are due to differences in their atoms.

Multiple Choice

Which statement best defines an atom?

• The smallest possible unit of an element

• A substance made of two or more different atoms

• A collection of different elements mixed together

• The largest part of a chemical substance

Multiple Choice

What makes a pure substance, like iron, qualify as an element?

• It is made of only one type of atom.

• It can be easily broken down into smaller parts.

• It is a liquid at room temperature.

• It is mixed with at least one other substance.

Multiple Choice

Based on the information provided, what is the fundamental reason that the element gold has different chemical properties than the element iron?

• The atoms of gold are different from the atoms of iron.

• Gold is a more valuable element than iron.

• One element is a solid and the other is a gas.

• They are made of different combinations of the same atoms.

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Identifying Substances by Their Properties

Physical Properties

• Properties you can observe or measure without changing the substance’s chemical identity.

• Examples are color, density, melting point, boiling point, and solubility in liquids.

• These characteristics are unique for every substance and help us identify them.

Chemical Properties

• Properties that describe how a substance reacts or combines with other substances.

• Examples of these properties include the substance's reactivity and its ability to burn.

• Observing these properties involves a chemical reaction that creates a new substance.

Multiple Choice

What is the main difference between a physical property and a chemical property?

• A physical property can be observed without changing the substance's identity, while a chemical property can only be observed by changing it.

• A physical property describes how a substance reacts, while a chemical property describes its appearance.

• A physical property is a characteristic that is unique to a substance, while a chemical property is not.

• A physical property involves a chemical reaction, while a chemical property does not.

Multiple Choice

Which of the following lists contains only physical properties?

• Reactivity, density, and color

• Melting point, density, and solubility

• Ability to burn, reactivity, and color

• Solubility, reactivity, and ability to burn

Multiple Choice

A scientist needs to identify an unknown substance. Which is the best explanation for how to proceed without creating a new substance?

• Observing its reactivity with acid, because this shows how it combines with other substances.

• Measuring its boiling point and density, because these are unique properties that do not change the substance.

• Testing its ability to burn, because this is a key chemical characteristic.

• Observing its color, because this is the easiest property to see without any equipment.

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Mendeleev's Periodic Table

• In 1869, Dmitry Mendeleev arranged 63 known elements from lightest to heaviest.

• He grouped elements with similar properties into columns, creating a periodic pattern.

• He left gaps for undiscovered elements and correctly predicted their properties.

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Multiple Choice

What was the primary method Dmitry Mendeleev used to group elements on his periodic table?

• He grouped them into columns based on similar properties.

• He ordered them alphabetically by their names.

• He arranged them according to their color.

• He listed them by the date they were discovered.

Multiple Choice

What was the result of arranging the elements by increasing weight and grouping them by properties?

• That a repeating, periodic pattern appeared among the elements.

• That arranging elements by weight was not useful.

• That all possible elements had already been found.

• That an element's properties were unrelated to its weight.

Multiple Choice

What did leaving gaps in the periodic table allow Mendeleev to demonstrate?

• The organizational pattern of the table could be used to predict the existence of unknown elements.

• There were mistakes in the arrangement of the 63 known elements.

• The table was considered complete and no new elements would be added.

• Grouping elements by properties was less important than ordering them by weight.

The Modern Periodic Table

• Elements are organized by their atomic number and properties.

• The table's structure helps predict the properties of an element.

• Color-coding distinguishes different families of elements like metals and nonmetals.

Multiple Choice

What is the primary basis for organizing elements on the modern periodic table?

• By their atomic number and properties

• By the date they were discovered

• By the color of the element

• By the person who discovered them

Multiple Choice

What is the main advantage of the periodic table's structured organization?

• It makes the table more colorful and easier to read.

• It helps in predicting an element's properties based on its location.

• It tells you the exact mass of every element.

• It only shows which elements are metals.

Multiple Choice

If an element is placed in a section of the periodic table far away from the color-coded 'metal' family, what can you most likely conclude about that element?

• It is likely a nonmetal with properties different from elements in the metal family.

• It must have the same atomic number as the metals.

• It will be a metal, just like all the other elements.

• It cannot be classified without knowing its color.

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Pioneers of Element Discovery

Sir Humphry Davy

• An English chemist who pioneered using electrolysis, a process that separates substances with electricity.

• He ran electricity through chemical solutions, which led to the discovery of new elements.

• Through this method, he discovered seven elements, including potassium and sodium for the first time.

Marie Curie

• A Polish-French physicist and chemist who conducted groundbreaking research on uranium ore.

• She discovered two new elements, polonium and radium, and also coined the term radioactivity.

• Marie Curie was the first person in history to win two Nobel Prizes.

Multiple Choice

What pioneering process did Sir Humphry Davy use to discover new elements like potassium and sodium?

• The process of electrolysis

• The study of radioactivity

• The analysis of uranium ore

• The invention of the Nobel Prize

Multiple Choice

How did the scientific methods of Sir Humphry Davy and Marie Curie differ?

• Davy discovered radioactive elements, while Curie discovered stable elements.

• Davy's work earned Nobel Prizes, while Curie's did not.

• Davy used electricity to separate elements, while Curie discovered elements by studying radioactive ore.

• Davy focused on chemistry, while Curie focused only on physics.

Multiple Choice

Based on the accomplishments of Davy and Curie, which of the following would also be considered a 'pioneer of element discovery'?

• A scientist who wins a prestigious award for their research.

• A scientist who confirms the existence of a known chemical.

• A scientist who uses a novel technique to identify a previously unknown substance.

• A scientist who writes a book about the history of chemistry.

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Elements: From Stardust to Everything

• Around 90 elements occur naturally, sometimes found in pure forms like gold and iron.

• Most elements combine to form new substances, like sodium and chlorine in table salt.

• All elements on Earth, including those in us, originated from exploding stars.

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Multiple Choice

What is the origin of all the elements that make up everything on Earth?

• They were created inside exploding stars.

• They were formed in the Earth's core.

• They are created by chemical reactions on Earth.

• They are transported to Earth by comets.

Multiple Choice

Which statement best describes how elements are typically found on Earth?

• Some elements are found in pure form, while most are combined with other elements.

• All elements are found in their pure form in nature.

• Elements can only be found combined into new substances.

• There are only two elements: sodium and chlorine.

Multiple Choice

Given that all elements on Earth originated from the same source, what can be concluded about the materials that make up the human body?

• The elements that make up our bodies originated in exploding stars.

• Our bodies are made of elements that are not found anywhere else on Earth.

• Our bodies are mostly made of pure elements like gold and iron.

• The human body is able to create its own unique elements.

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Common Misconceptions

Misconception	Correction
An element is the same as a substance.	An element is a pure substance made of only one type of atom.
A substance's properties change if you have more of it.	Characteristic properties like density and boiling point do not change with the amount.
The periodic table is just a random list of elements.	The periodic table groups elements with similar, predictable physical and chemical properties.

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Summary

• An element is a pure substance made of only one type of atom.

• Substances are identified by their unique physical and chemical properties.

• The periodic table groups elements based on their repeating properties.

• Scientists discovered new elements using methods like electrolysis and radioactivity.

• All matter on Earth is made from about 90 naturally occurring elements.

• Most substances are combinations of elements, creating new materials.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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