Warmup 10/27/15 God designed the universe so that everything we see is made of atoms and combinations of atoms. So look at the periodic table: How many combinations do you think we can make by just combining elements in pairs? (Use some estimation skills for this!) Objective Tonight’s Homework To learn how elements can combine None

Notes on Compounds A compound is a combination of two or more elements. We can’t just combine any elements though. There are rules for how they combine. We’re going to look at a few examples But first, a basic rule on how to recognize what’s an element and what’s a compound. Elements are usually reactive and want to combine with other things. Compounds don’t react so much and are fairly stable.

Notes on Compounds Example: Salt Physical properties: - A white solid at room temperature - Crystals shaped like cubes - Crystals are hard but brittle (break easily) - High melting temperature (800 o C) - Solid does not conduct electricity - Easily dissolves in water - Salt solutions are excellent conductors of electricity

Notes on Compounds Table salt is made of Sodium and Chlorine and has the chemical formula “NaCl” In chemical formulas we just stick the letters for each element next to each other. Sodium + Chlorine  Na + Cl  NaCl Sodium Chloride is a very stable compound. This means it does not react much with other substances. For example, it could sit in a salt shaker for hundreds of years and still remain salt.

Notes on Compounds When we make a compound, it’s often very different from the elements that go into it. Let’s look at the elements that make up salt. Sodium: - Sodium is a shiny, silvery-white, soft, solid element. -Sodium melts at 98 o C - Sodium is highly reactive and reacts violently with water.

Notes on Compounds Chlorine: -Chlorine is a pale green, poisonous gas with a choking odor. -Chlorine gas was used in WWI for chemical warfare because it kills living cells. -Slightly soluble in water so is used as a disinfectant -One of the most reactive elements.

Notes on Compounds It’s important to note here that sodium and chlorine both have their own properties and that when we combine them, we get something with new properties. These properties don’t have to be similar at all to the elements it’s made of. It's also important to note that while sodium and chlorine are reactive, we put them together and get something that isn't reactive. Elements are reactive, compounds aren't!

Mythbusters Let’s watch some mythbusters to illustrate these concepts.

Exit Question What is salt made of? a) Sodium and Chlorine b) Salt c) Ions and Isotopes d) Little white rocks e) No one knows f) None of the above