Pure Substances Elements/Compounds

Chemistry: Chemistry: is the study of the properties of matter and how matter changes. Click the thinking man for a quick video

Element: Element: a substance that cannot be broken down into any other substances by chemical or physical means. You would not confuse a doghouse with an airport terminal or a gas station. These buildings are constructed differently, with different materials such as bricks, wood, glass, stone, concrete, and steal. Using these same materials, people have built many different structures.

Element: Continued Just like different buildings are made from a few kinds of materials, all the different kinds of matter in the universe are made from about 100 different substances called elements. Ex: copper in pennies, aluminum in foil, tungsten in light bulbs.

Compounds: Most elements are not found in their pure form in nature. They are mostly found as parts of compounds. Compound: Is a substance made of 2 or more elements chemically combined in a specific ratio or proportion. Ex: CO₂ You breath it out of you lungs It’s made of 1 Carbon (C) & 2 Oxygen (O)

Compound: Continued Ratio: compares numbers, it tells you how much you have of 1 item in comparison to how much you have of another. Ex: a recipe for cookies may call for 2 cups of flour for every 1 cup of sugar. You could write this ratio as: 2 to 1 or 2:1

Compound: Continued The elements in a compound are present in specific ratios. If 2 compounds contain the same elements in different ratios, they are different compounds. Both Methane and Ethane have Carbon (C) and Hydrogen (H), however, they both have different ratios of the two elements which makes them different compounds.

Compound: Continued + + = Sugar C₆H₁₂O₆ is a compound that contains the following: (C) Carbon- by its self is a black powder (H) Hydrogen is a colorless gas (O) Oxygen is a colorless gas When elements combine the resulting compound (like sugar) has different properties, than the elements that make it. + + =

Pure Substance: Pure Substance: element or compound that cannot be broken down into simpler components and maintain the properties of the original substance. Ex: helium, aluminum, water, & salt

Pure Substance Each pure substance has physical and chemical properties that can be used to identify it.

If you have water and then pull out the two hydrogen and pull out the oxygen, those elements, individually, do NOT have the same properties as water. Does not have the same properties as water when it is by itself. Does not have the same properties as water when it is by itself.

Mixtures Mixture: 2 or more pure substances, elements, compounds or both – that are in the same place but not chemically combined. Example: soil  the parts can be in varying ratios. The different parts of a mixture keep their individual properties and can be easily seen. Solution: this is a well-mixed mixture where individual substances can’t be seen easily. Ex: salt water You can’t see the salt in the water, but if you tasted it you would. You could also separate this solution by letting it dry in the sun.

Changes in Matter: There are 2 changes in Matter. Physical Chemical Click the question mark to watch a clip of the difference between a physical change and a chemical change.

Physical Change: A change that alters the form or appearance of a material but does not make the material into another substance. Ex: H₂O or water You can change ice into a liquid by leaving an ice cube out, or boil it to make it gas. It is still made of the same elements 2 hydrogen (H), and 1 Oxygen (O).

Chemical Change: Chemical Change: A change in matter that produces a new substance. The new substances are made of the same elements as the original substance, but now are in different combinations, and now have new properties. Ex: Salt or Sodium Chloride is made of the following: Hydrochloric Acid (HCl): it is poisonous, and will burn you Sodium (Na): it will blow up in the presents of oxygen But when chemically combined these two substance form something edible.

Chemical Change: Continued Hydrochloric Acid (HCl): Sodium (Na):

Chemical Change: Continued Chemical reaction: The process in which substances undergo chemical changes that result in the formation of new substance. Ex: Car rusting, wood burning, You can’t get the original elements back! The key characteristics of a chemical reaction is the production of new materials that are chemically different from the starting material.

Evidence for Chemical Reactions: Color change: leaves changing in the fall Gas production: bubbles on a cut after using peroxide. Change in temperature: hand warmers getting hot Precipitation: when 2 clear liquids are mixed it will form a solid. Change in properties: Baking a cake it is a liquid when you put it in the oven, then becomes light and fluffy.

Atoms & Molecules: Atom: The smallest particle of an element. Or in other words 1 element Ex: Carbon C Just how small is an atom? Watch this video of a book and think about how small the top of the rooster’s head is at the very end.

Atoms & Molecules: Molecule: is a particle made of 2 or more atoms bonded together. Some molecules are made of atoms that are alike like Oxygen (0₂) gas you breath. Most are made of more than 1 type of atom. Water molecules have 2 hydrogens (H) atoms combined with 1 oxygen (O) atom to make H₂O. All compounds are molecules.

Simple & Complex Molecules: Simple Molecules: Complex Molecule: composed of many interconnected parts or subunits, can contain hundreds or thousands of bonds. Also known as polymers. Ex: Sodium Chloride, diamonds. Simple Molecule: contains 1 or few bonds, they are small. Also known as monomers. Ex: Ammonia, and Methanol

Simple Molecules: Ammonia: NH₃ Methanol: CH₄O

Complex Molecules Diamond Sodium Chloride