Download 1. Name: Chapter 4 Elements and Compounds

Elements and
Compounds
Chapter 4B

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/
What is a Compound?
 Definition: A pure substance which can be broken
down into elements via chemical reactions.
 Examples: See compound box
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
Compounds vs. Mixtures
Compound
Mixture
 Properties of Compounds are
different from those of
components –
+ Cl = NaCl
Na
 Properties of a mixture are a
combination of the properties of
the components ethanol +
water
 Definite Composition
 Variable Composition
 Cannot be separated by
 CAN be separated by physical
Physical Processes
means
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
Try It!
 Write chemical formulas for molecules
composed of
1. One iron atom and one oxygen atom
2. One carbon atom and four hydrogens
3. One hydrogen, one carbon, and one
nitrogen atom.
Natural Abundances
 Universe:
 91% Hydrogen
 9% Helium
 Earth’s Crust
 60.1 % Oxygen
 20.1 % Silicon
 6.1 % Aluminum
 2.2 % Iron
 1.5% All others
2.9% Hydrogen
2.6% Calcium
2.4 % Magnesium
2.1 % Sodium
Natural Abundances
 Human Body
 63 % Hydrogen
 25.5 % Oxygen
 9.5 % Carbon
 1.4 % Nitrogen