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

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 H2O 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 % Hydrogen
20.1 % Silicon % Calcium
6.1 % Aluminum % Magnesium
2.2 % Iron % Sodium
1.5% All others

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