Chemistry Building Blocks 4/30/2012

BR: Identify element based on symbol For each element symbol (letter or letters), determine what element it is O N H C

Elements Elements are pure substances that cannot be separated into simpler substances by either physical or chemical changes.

Legos! Each Lego block represents one atom. Remove the Legos from the bag and sort by color. Each color is a different element. To create compounds, you will need to connect the Legos to each other (representing chemical bonds). To create mixtures, you will need to group Legos together without connecting them. The number to the right of each letter tells you how many of each element you need. If there is no number, that means just one atom of that element.

Atoms, Molecules, and Compounds TERMDEFINITIONLEGO EQUIVALENT AtomThe smallest unit of an element that has the properties of that element MoleculeComposed of two ore more atoms that are joined by chemical bonds (can be the same element or different elements) CompoundPure substance composed of two or more different elements joined by chemical bonds

Construct & illustrate... Make an oxygen atom Make an oxygen molecule (O 2 ) Make a carbon dioxide molecule (CO 2 ) Make a water molecule (H 2 O) Make a nitrogen molecule (N 2 ) Which of these are compounds? Which are pure elements (either atoms or molecules of just one element)?

Compounds Made of elements in a specific ratio that is always the same [H 2 O (water) is VERY different from H 2 O 2 (hydrogen peroxide)] Can only be separated by chemical changes, not physical changes Have their own physical & chemical properties that can be different from what they're made of... EX. H 2 O is water, which is a liquid at room temperature although H and O are both gases at room temperature

HW: Elements, Compounds, & Mixtures Assignment

BR 5/1 Identify whether each substance or combination of substances is a pure element, a compound, or a mixture of elements or compounds. Write down the chemical formulas in addition to your response. O 2 O 2 & He CO 2 C 2 H 6 O and H 2 O O 2, H 2 O, N 2, and CO 2

Illustrating elements, compounds, & mixtures Identify which image represents each item in the BR.

Mixtures A mixture is a combination of two or more pure substances that are not chemically combined. Substances are held together by physical forces, not chemical ones No chemical change takes place when you make a mixture Each part of the mixture keeps the same properties it had before it was mixed Mixtures can be separated physically

Mixtures Homogeneous mixtures are when molecules are mixed up in an even distribution (so if you take two samples from separate parts of the mixture, they should be identical) EX: sugar water, lemonade, Kool-Aid, soda, air

Mixtures Heterogeneous mixtures are when molecules are not mixed up in an even distribution EX: snow globe, muddy water

Demo: 4 Mixtures Each person will measure 10 mL of distilled water using a graduated cylinder and put it in a separate cup. Volunteer 1 will then measure in 1 tsp of table salt and mix with a stirring rod. Volunteer 2 will then measure in 2 tsp of table salt and mix with a stirring rod. Volunteer 3 will then measure in 3 tsp of table salt and mix with a stirring rod. Volunteer 4 will then measure in 4 tsp of table salt and mix with a stirring rod.

Observations... What are the differences you observe between each of our mixtures? Did the salt fully dissolve in each sample, or is there still solid salt in any sample? Which mixtures are homogeneous and which are heterogeneous based on your visual observations? Properties of each solution: need 4 new volunteers...

Demo Part 2: Measuring Conductivity Each person will use a 1.5 V battery and a multimeter to measure the conductivity of their solution (I will show how to connect the circuit). What do you observe about each sample? Which sample conducts the most electricity (highest number)? What is the relationship between salt concentration (amount per mL of water) and conductivity?