compounds

structure of compounds

Compounds like sodium chloride form structures called crystals. A crystal is a rigid framework of many ions locked together in a repeating pattern. Ions are electrically charged forms of atoms. You can see a crystal of sodium chloride in the Figure 1.3. It is made up of many sodium and chloride ions. Sodium and chlorine combine to form sodium chloride, or table salt. A sodium chloride crystal consists of many sodium ions (blue) and chloride ions (green) arranged in a rigid framework. Click image to the left or use the URL below. URL: Compounds such as carbon dioxide and water form molecules instead of crystals. A molecule is the smallest particle of a compound that still has the compounds properties. It consists of two or more atoms bonded together. You saw models of carbon dioxide and water molecules above.

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properties of compounds

The properties of compounds are different from the properties of the elements that form themsometimes very different. Thats because elements in a compound combine and become an entirely different substance with its own unique properties. Do you put salt on your food? Table salt is the compound sodium chloride. It contains sodium and chlorine. As shown in the Figure 1.2, sodium is a solid that reacts explosively with water, and chlorine is a poisonous gas. But together in table salt, sodium and chlorine form a harmless unreactive compound that you can safely eat. Q: The compound sodium chloride is very different from the elements sodium and chlorine that combine to form it. What are some properties of sodium chloride? A: Sodium chloride is an odorless white solid that is harmless unless consumed in large quantities. In fact, it is a necessary component of the human diet.

what is a compound

A compound is a unique substance that forms when two or more elements combine chemically. For example, the compound carbon dioxide forms when one atom of carbon (grey in the model above) combines with two atoms of oxygen (red in the model). Another example of a compound is water. It forms when two hydrogen atoms combine with one oxygen atom. Click image to the left or use the URL below. URL: Q: How could a water molecule be represented? A: It could be represented by a model like the one for carbon dioxide in the opening image. You can see a sample Figure 1.1. A model of water. Two things are true of all compounds: A compound always has the same elements in the same proportions. For example, carbon dioxide always has two atoms of oxygen for each atom of carbon, and water always has two atoms of hydrogen for each atom of oxygen. A compound always has the same composition throughout. For example, all the carbon dioxide in the atmosphere and all the water in the ocean have these same proportions of elements. Q: How do you think the properties of compounds compare with the properties of the elements that form them? A: You might expect the properties of a compound to be similar to the properties of the elements that make up the compound. But you would be wrong.

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instructional diagrams

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questions

which of the following is a compound?

a) air

b) oxygen

-->  c) carbon dioxide

d) two of the above

a compound always has the same elements in the same proportions.

-->  a. true

b. false

the properties of compounds are the same as the properties of the elements that form them.

a. true

-->  b. false

which of the following substances is a compound that forms ionic crystals?

a) water

-->  b) sodium chloride

c) carbon dioxide

d) none of the above

which of the following gases is a compound that forms molecules?

a) air

-->  b) carbon dioxide

c) oxygen

d) nitrogen

a molecule consists of two or more atoms bonded together.

-->  a. true

b. false

diagram questions

No diagram questions associated with this lesson