15.1 Classification of Matter

Review

• Chemistry: the study of matter and how it changes

• Matter: anything that has mass and occupies space

Classifying Matter

• Element: a substance that cannot be broken down into simpler substances

• Atom: the smallest particle that has the properties of an element

Atoms of the same element are exactly alike!

• Compound: a substance made of atoms of more than one element chemically bound together

Every compound is unique and is different from the elements that it contains.

Salt is also known as sodium chloride because it contains atoms of both sodium and chlorine. Both very hazardous and toxic elements by themselves, but together make a compound that is found in almost every meal.

Compounds to have atoms of different elements….only one type of atom bound together is a molecule

Example: gases such as Oxygen ( O2), Hydrogen (H2), and Chlorine (Cl2)

• Molecule: the smallest unit of a substance that exhibits all of the properties characteristic of that substance

Example: A glass of water contains millions of water molecules.

Chemical formulas are used to represent compounds and molecules.

1 molecule

Compound

1 molecule

• Chemical formula: the chemical symbols and numbers indicating the atoms contained in the basic unit of a substance

Chemical formula for caffeine is 3 C8H10N4O2

The numbers written below and to the right of the element’s symbol identifies how many atoms of that element are present.

Carbon = 8 atoms

Hydrogen = 10 atoms

Nitrogen = 4 atoms

Oxygen = 2 atoms

The number to the far left of the formula represents how many molecules of that compound are present.

There are 3 caffeine molecules represented by the formula above.

• Pure substance: any matter that has a fixed composition and definite properties

Pure substances have a set chemical formula. A pure substance only can be broken down by breaking bonds, but then it is no longer that substance. If we separate the Na from Cl in NaCl (salt), we do not have salt anymore.

Many products that we buy claim to be “pure”, such as honey or juices. However, they are made of several different types of sugars, acids, vitamins, minerals, water,…..etc.

• Mixture: a combination of more than one pure substance

Mixtures can be separated without breaking bonds. (ie sifting, boiling, sorting, …)

If you have a mixture of rocks and sand…you can just pick out the rocks.

Mixtures can be classified as:

Heterogeneous: substances that are not uniformly mixed

Homogeneous: substances that are uniformly mixed

Solutions (liquid mixtures)

• Miscible: describes two or more liquids that are able to dissolve into each other in various proportions

• Immiscible: describes two or more liquids that do not mix into each other.

• Colloid- a type of mixture with particles larger than those in solutions but not heavy enough to settle out– Tyndall effect-scattering of light by colloidal

particles

Suspension- heterogeneous mixture containing a liquid in which particles settle out

PracticeGive an example for each of the following!

Matter Element Mixture Compound Chemical formula Pure substance Heterogeneous mixture Homogeneous mixture Miscible solution Immiscible solution