2.3 Elements and Compounds

Physical methods that are used to separate mixtures cannot be used to break a compound into simpler substances.

Boil liquid water and you get water vapor, not the oxygen and hydrogen that water contains. Dissolve a sugar cube in water and you still have sucrose, not oxygen, carbon, and hydrogen. This does not mean that sucrose or water cannot be broken down into simpler substances. But methods must involve a chemical change.

There is a key difference between elements and compounds.

Compounds can be broken down into simpler substances by chemical means, but elements cannot.

The symbols used today for elements

Each element is represented by a one- or two-letter chemical symbol. First letters of chemical symbols are capitalized. When a second letter is used, it is lowercase.

No matter what you do to a silvery liquid, it doesn't seem to change. Is it more likely to be a substance or a mixture?

It is most likely a substance. If it was a mixture, it would likely have separated when manipulated chemically or physically.

In general, the properties of compounds are quite different from those of their component elements.

Sugar is a sweet-tasting white solid, but carbon is a tasteless black solid. The product of this chemical change is water, a liquid that can stop materials from burning.

Can the substances that are produced when sugar is broken down when heated also be broken down?

There is no chemical process that will break down carbon into simpler substances because carbon is an element.

chemical change

a change that produces matter with a different composition than the original matter.

element

element is the simplest form of matter that has a unique set of properties. Oxygen and hydrogen are two of the more than 100 known elements.

Substances can be classified as

elements or compounds.

vertical column

group

compound

is a substance that contains two or more elements chemically combined in a fixed proportion.

horizontal row of the periodic table

period

If the composition of a material is fixed, the material is a _________. If the composition of a material may vary, the material is a ______

substance mixture