How is
Chemistry
defined?
Notes: Introduction to Chemistry Ch. 1.1-1.3
Def: The science of materials of the universe and the changes
they undergo
*Most of the phenomena that occur in the world around us
involve chemical changes
Examples:
-Burning wood
-Turning on a car
-Baking
-Rusting
-Photosynthesis
What are
these
materials
made of?
Matter – Anything with mass that occupies space
-All matter is composed of elements
-Each element is uniquely composed of different atoms
-i.e. H atoms have 1 proton and 1 electron
C atoms have 6 protons and 6 electrons
O atoms have 8 protons and 8 electrons
-Molecules– different combinations of atoms
-i.e. 2H atoms + 1O atom = 1H2O molecule
Law of
Pure compounds always have the same elemental proportions.
Constant
-i.e. Water (H2O) always has 2:1 Hydrogen:Oxygen ratio
Composition
States of
Matter
Solids: Have definite shape and volume
Liquids: Have definite volume; take the shape of their container
Gases: Take on both the shape and volume of their container
Substances
and Mixtures
Substances (aka pure substances)
-Entirely composed of a single element or compound
-i.e. Helium gas, purified water (H2O)
Mixtures
-Homogeneous (solutions): mixture is completely uniform
-i.e. steel, brass, kool aid, store-bought milk
-Heterogeneous: mixture is not uniform / inconsistent
-i.e. rock (ore), pond water, fresh milk
Physical vs.
Chemical
Properties
Physical Properties: measured without changing composition of
the substance
-i.e. color, density, melting point, boiling point
Chemical Properties: describe how substance will react
-i.e. electronegativity, flammability
Physical
Changes vs.
Chemical
Changes
Practice:
Physical Changes: Appearances change, but chemical
composition stays the same. All state changes (solid, liquid,
gas) are physical.
-i.e. Ice, Water and Water Vapor are all H2O
Chemical Changes: Substances transformed chemically into
other substances
-i.e. Hydrogen gas burns in oxygen to create water
-2H2 + O2  2H20
Element, Molecule or Compound?
-Au
-CO2
-CH4
-N2
Physical or Chemical?
-A tree is cut down and turned into lumber
-The statue of liberty turning green
-Copper is drawn into small wires for electronics
-Plants converting sunlight into usable, stored energy