Set up Cornell Notes on pages 73, Set up Cornell Notes on pages 73, 75, 77 & 79 75, 77 & 79 Summary section (about 1/3 of the

page) on page 79

Elements, Compounds &

Mixtures

www.middleschoolscience.com 2008

• A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. • In the animation above, two oxygen atoms (O + O = O2) make one oxygen molecule .

Pure Pure SubstancesSubstances

DNA—deoxyribonucleic acid•DNA is a very large molecule in

the shape of a double helix.•The rungs of the ladder are called

bases—adenine, thymine, guanine & cytosine.

•The sides of the ladder are made of phosphate and sugar molecules.

•Components of the DNA molecule are carbon, hydrogen, nitrogen, oxygen, and phosphorous.

•Each substance in a mixture keeps its individual properties.

•Each substance in a mixture is not always in the same ratio to the other substances.

•Making a mixture is a PHYSICAL CHANGE, not a chemical change.

•Mixtures will either be▫Homogeneous (you cannot see the different parts) OR

▫Heterogeneous (you can see the different parts)

• Solutions are groups of molecules that are mixed up in a completely even distribution.•Solutions are types of mixtures.

• Uniform Distribution.• Example: Sugar and Water

Images are from http://www.chem4kids.com

• The substance to be dissolved.

• The one doing the dissolving.

Images are from http://www.chem4kids.com

• They are substances held together by physical forces, not chemical.•Can be separated physically.

• The substances are not uniformly mixed.

• Example: Sand in a glass of water.Images are from http://www.chem4kids.com

• Are heterogeneous mixtures consisting of parts that are visible to the naked eye.

Example: the ingredients in salad dressing

• Substances will settle over time.

• Particle sizes are in between the size of particles found in solutions and suspensions .

• Can be mixed and remain evenly distributed without settling out.