types of matter

history of elements

The idea of elements is not new. It dates back about 2500 years to ancient Greece. The ancient Greek philosopher Aristotle thought that all matter consists of just four elements. He identified the elements as earth, air, water, and fire. He thought that different kinds of matter contain only these four elements but in different combinations. Aristotles ideas about elements were accepted for the next 2000 years. Then, scientists started discovering the many unique substances we call elements today. You can read when and how each of the elements was discovered at the link below. Scientists soon realized that there are far more than just four elements. Eventually, they discovered a total of 92 naturally occurring elements.

properties of elements

Each element has a unique set of properties that make it different from all other elements. As a result, elements can be identified by their properties. For example, the elements iron and nickel are both metals that are good conductors of heat and electricity. However, iron is attracted by a magnet, whereas nickel is not. How could you use this property to separate iron objects from nickel objects?

elements

An element is a pure substance. It cannot be separated into any other substances. There are more than 90 different elements that occur in nature. Some are much more common than others. Hydrogen is the most common element in the universe. Oxygen is the most common element in Earths crust. Figure 3.7 shows other examples of elements. Still others are described in the video below. MEDIA Click image to the left or use the URL below. URL:

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molecules and crystals

The smallest particle of a compound that still has the compounds properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure 3.10). You can learn more about molecules at this link: Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure 3.11). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. You can actually watch crystals forming in this video: .

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properties of compounds

A compound has different properties than the substances it contains. For example, hydrogen and oxygen are gases at room temperature. But when they combine chemically, they form liquid water. Another example is table salt, or sodium chloride. It contains sodium and chlorine. Sodium is a silvery solid that reacts explosively with water, and chlorine is a poisonous gas (see Figure 3.9). But together, sodium and chlorine form a harmless, unreactive compound that you can safely sprinkle on food.

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compounds

There are millions of different substances in the world. Thats because elements can combine in many different ways to form new substances. In fact, most elements are found in compounds. A compound is a unique substance that forms when two or more elements combine chemically. An example is water, which forms when hydrogen and oxygen combine chemically. A compound always has the same components in the same proportions. It also has the same composition throughout. You can learn more about compounds and how they form by watching this video: MEDIA Click image to the left or use the URL below. URL:

elements and atoms

The smallest particle of an element that still has the elements properties is an atom. All the atoms of an element are alike, and they are different from the atoms of all other elements. For example, atoms of gold are the same whether they are found in a gold nugget or a gold ring (see Figure 3.8). All gold atoms have the same structure and properties.

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particle size in mixtures

Mixtures have different properties depending on the size of their particles. Three types of mixtures based on particle size are described below. Figure 3.13 shows examples of each type. You can watch videos about the three types of mixtures at these links: MEDIA Click image to the left or use the URL below. URL: MEDIA Click image to the left or use the URL below. URL: A solution is a homogeneous mixture with tiny particles. An example is salt water. The particles of a solution are too small to reflect light. As a result, you cannot see them. Thats why salt water looks the same as pure water. The particles of solutions are also too small to settle or be filtered out of the mixture. A suspension is a heterogeneous mixture with large particles. An example is muddy water. The particles of a suspension are big enough to reflect light, so you can see them. They are also big enough to settle or be filtered out. Anything that you have to shake before using, such as salad dressing, is usually a suspension. A colloid is a homogeneous mixture with medium-sized particles. Examples include homogenized milk and gelatin. The particles of a colloid are large enough to reflect light, so you can see them. But they are too small to settle or filter out of the mixture.

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homogeneous and heterogeneous mixtures

Some mixtures are homogeneous. This means they have the same composition throughout. An example is salt water in the ocean. Ocean water everywhere is about 3.5 percent salt. Some mixtures are heterogeneous. This means they vary in their composition. An example is trail mix. No two samples of trail mix, even from the same package, are likely to be exactly the same. One sample might have more raisins, another might have more nuts.

mixtures

Not all combined substances are compounds. Some are mixtures. A mixture is a combination of two or more substances in any proportion. The substances in a mixture may be elements or compounds. The substances dont combine chemically to form a new substance, as they do in a compound. Instead, they keep their original properties and just intermix. Examples of mixtures include salt and water in the ocean and gases in the atmosphere. Other examples are pictured in Figure 3.12.

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separating mixtures

The components of a mixture keep their own identity when they combine. Therefore, they usually can be easily separated again. Their different physical properties are used to separate them. For example, oil is less dense than water, so a mixture of oil and water can be separated by letting it stand until the oil floats to the top. Other ways of separating mixtures are shown in Figure 3.14 and in the videos below. (2:30) MEDIA Click image to the left or use the URL below. URL: (2:41) MEDIA Click image to the left or use the URL below. URL:

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instructional diagrams

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questions

homogeneous mixture in which particles are too small to be seen

a. colloid

b. compound

c. element

d. mixture

-->  e. solution

f. suspension

g. crystal

The most common element in Earths crust is

a. water.

b. iron.

c. hydrogen.

-->  d. oxygen.

combination of two or more substances in any proportions

a. colloid

b. compound

c. element

-->  d. mixture

e. solution

f. suspension

g. crystal

The smallest particle of an element that still has the elements properties is a(n)

a. crystal.

b. compound.

-->  c. atom.

d. molecule.

homogeneous mixture in which particles are big enough to reflect light

-->  a. colloid

b. compound

c. element

d. mixture

e. solution

f. suspension

g. crystal

Aristotle thought there were four elements, including

a. air.

b. earth.

c. water.

-->  d. all of the above.

Whenever elements combine physically, they form

-->  a. mixtures.

b. solutions.

c. compounds.

d. suspensions.

heterogeneous mixture

a. colloid

b. compound

c. element

d. mixture

e. solution

-->  f. suspension

g. crystal

unique substance that forms when two or more elements combine chemically

a. colloid

-->  b. compound

c. element

d. mixture

e. solution

f. suspension

g. crystal

Which of the following is the best example of a heterogeneous mixture?

-->  a. raisin bran

b. milk

c. orange juice

d. water

rigid, lattice-like framework of many ions bonded together

a. colloid

b. compound

c. element

d. mixture

e. solution

f. suspension

-->  g. crystal

pure substance that cannot be separated into any other substances

a. colloid

b. compound

-->  c. element

d. mixture

e. solution

f. suspension

g. crystal

I am lighter than air and used to fill balloons. Which element am I?

a. neon

b. carbon

c. oxygen

-->  d. helium

Iron and nickel are both

a. elements.

b. metals.

c. compounds.

-->  d. two of the above.

Which statement is false about the atoms of a given element?

a. They are all alike.

-->  b. They are the same as the atoms of all other elements.

c. They have properties of the given element.

d. They all have the same structure.

Atoms of the same element are all alike.

-->  a. true

b. false

John Dalton made all the following contributions to our knowledge of atoms except

a. doing research to show atoms exist.

b. introducing modern ideas about atoms.

c. developing a theory of the atom.

-->  d. arguing that atoms do not exist.

Each compound has a unique set of properties.

-->  a. true

b. false

Which drink is an example of a compound?

a. lemonade

b. ice tea

c. vanilla milkshake

-->  d. water

An example of a heterogeneous mixture is

a. salt water.

b. gelatin.

c. milk.

-->  d. trail mix.

Atoms can be seen with a hand lens.

a. true

-->  b. false

Which mixture has the largest particles?

-->  a. muddy water

b. salt water

c. milk

d. lemonade

There are millions of different elements in the universe.

a. true

-->  b. false

A crystal consists of molecules that are bonded together.

a. true

-->  b. false

Each element has a unique set of properties.

-->  a. true

b. false

The idea of elements was first introduced by John Dalton.

a. true

-->  b. false

Most elements are found in compounds.

-->  a. true

b. false

A compound has the same properties as the substances it contains.

a. true

-->  b. false

A molecule consists of two or more atoms.

-->  a. true

b. false

Table salt is an example of a compound that forms molecules.

a. true

-->  b. false

The substances in a mixture may be elements or compounds.

-->  a. true

b. false

A package of mixed seeds is a homogeneous mixture.

a. true

-->  b. false

Mixtures are classified on the basis of particle size.

-->  a. true

b. false

Components of mixtures rarely can be separated.

a. true

-->  b. false

diagram questions

No diagram questions associated with this lesson