Elements and Compounds

1. Elements and Compounds • Chapter 4B 

2. What is an Element? • Definition: A pure substance that can not be broken down into simpler pure substances via chemical reactions. • Examples: See element box • The 94 Elements Project: Copper • http://www.94elements.com/

3. What is a Compound? • Definition: A pure substance which can be broken down into elements via chemical reactions. • Examples: See compound box

4. Naming and Symbolizing Elements and Compounds • Chemical Symbols for Elements – One or Two letter code • Helpful to memorize 1st 20 plus Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Ag, I, Au, Hg • Chemical Formulas for Compounds – Show how many of each type of atom is bonded together to form a molecule. • Examples: H2O H2O2 CuO HNO3

5. Compounds vs. Mixtures • Compound Mixture • Properties of Compounds are different from those of components – Na + Cl = NaCl • Definite Composition • Cannot be separated by Physical Processes • Properties of a mixture are a combination of the properties of the components - ethanol + water • Variable Composition • CAN be separated by physical means

6. Atoms and Molecules • Atoms = smallest particle unique to an element. • Molecule = group of atoms chemically connected or bonded together. Acquires distinct properties. • Diatomic molecules = Two atoms of same type. • Homoatomic molecule = one kind of atom • Heteroatomic molecule = two or more different kinds of molecules. • Molecules = Represented by chemical formulas

7. Try It! • Write chemical formulas for molecules composed of • One iron atom and one oxygen atom • One carbon atom and four hydrogens • One hydrogen, one carbon, and one nitrogen atom.

8. Natural Abundances • Universe: • 91% Hydrogen • 9% Helium • Earth’s Crust • 60.1 % Oxygen 2.9% Hydrogen • 20.1 % Silicon 2.6% Calcium • 6.1 % Aluminum 2.4 % Magnesium • 2.2 % Iron 2.1 % Sodium • 1.5% All others

9. Natural Abundances • Human Body • 63 % Hydrogen • 25.5 % Oxygen • 9.5 % Carbon • 1.4 % Nitrogen