Substances, Compounds & Mixtures

Substances, Compounds & Mixtures How everything is put together.

Substances • Matter that has the same composition and properties throughout is called a substance. • When different elements combine, other substances are formed.

Substances • Contains only one particle • Can exist in 3 states of matter • Can be elements or compounds Picture from http://www.ilpi.com/msds/ref/gifs/statesofmatter.gif

Compounds • A compound is a substance whose smallest unit is made up of atoms of more than one element bonded together. • Compounds often have properties that are different from the elements that make them up. • Every compound has a unique set of properties. • Examples: Water, salt, sugar

Compounds Have Formulas • Elements combine in a definite ratio to form a compound. • H20 is the chemical formula for water, and H2O2 is the formula for hydrogen peroxide. • The formula tells you which elements make up a compound as well as how many atoms of each element are present.

How to read a formula H20 This is a subscript. It tells us how many atoms of that element exist in one unit of that compound. Hydrogen is made of 2 H (hydrogen) atoms and 1 O (oxygen) atom. No subscript is used when only one atom of an element is present.

For Example • Water: H2O 2 atoms of hydrogen and 1 atom of oxygen. As long as the ratio stays the same (in this case 2:1) it is still water (H12O6) • Carbon Dioxide: CO2 Will still be carbon dioxide at C6O12

For Example • If the ratio changes, the compound changes. • By adding one more oxygen atom water (H2O) becomes hydrogen peroxide (H202). Very different. • Taking away one oxygen atom from carbon dioxide (CO2) makes carbon monoxide (CO). Also, very different.

Common Compounds • Salt: sodium chloride= NaCl (sodium and chloride) • Water: H2O (hydrogen and oxygen) • Carbon Dioxide: CO2 (carbon and oxygen) • Sugar: C12H22O11 (carbon, hydrogen, and oxygen) • Baking Soda: sodium bicarbinate= NaHCO3 (sodium, hydrogen, carbon, and oxygen)

Let’s try it… • Raise your hand if you know which elements are present in each of the following compounds. How many atoms of each are present? • Sulfuric Acid H2SO4 • Calcium Carbonate CaCO3 (Found in shells, eggshells, antacid)

Mixtures • When two or more substances (elements or compounds) come together but don’t combine to make a new substance, a mixture results.

The separate substances in a mixture retain their identity because no chemical change occurs.

Mixtures combine physically in no specific proportions. They just mix.

Solids, liquids and gases can be combined to create a mixture.

Mixture Types • Mixtures may be: • Homogeneous • Heterogeneous

Homogeneous Mixtures • Homogeneous Mixtures • Have the same uniform appearance and composition throughout • You cannot see the separate parts. • Solutions are homogenous mixtures

What is a solution? • A solution is a mixture of two or more substances. • At least two substances must be mixed in order to have a solution • A solution has two parts: • The substance in the smallest amount, and the one that DISSOLVES is called the SOLUTE • The substance in the larger amount is called the SOLVENT - it does the dissolving • IN most common instances water is the solvent.

Examples of homogenous mixtures (solutions) • Salt water • Clean Air • Vinegar • Your blood

Heterogeneous Mixtures: • A heterogeneous mixture consists of visibly different substances or phases. • Two or more parts can be seen.

Examples: • Pizza • Sandwich • Chex Mix • Salad

Suspensions • A SUSPENSION is a heterogeneous mixture of large particles • These particles are visible and will settle out on standing • Examples of suspensions are: fine sand or silt in water or Italian salad dressing

Compounds vs. Mixtures Mixtures Compounds Not chemically combined Combine chemically forming molecules Can combine in any proportion Combine in set proportions Separated chemically Separated physically Examples: salt baking soda oxygen Examples: pizza salad salt water your blood

Substances, Compounds & Mixtures