Sometimes I pretend to be normal, but then it gets boring, so I go back to
being me.
Is it possible to vary the
ratios of the components?
NO
PURE SUBSTANCE
Only one kind of atom?
YES
MIXTURE
Does it appear uniform throughout?
YES
YES
ELEMENT
NO
MOLECULE
NO
HOMOGENEOUS
HETEROGENEOUS
PHASE
SOLID
LIQUID
GAS
MACROSCOPIC VIEW
MOLECULAR/ATOMIC VIEW
DEFINITE VOLUME
AND SHAPE
ATOMS/MOLECULES ARE
PACKED TIGHTLY TOGETHER
SO THAT THEY CAN’T MOVE
AROUND EACH OTHER
DEFINITE VOLUME
BUT NO DEFINITE
SHAPE, FILLS
CONTAINER IT IS IN
FROM BOTTOM TO
TOPE
ATOMS/MOLECULES ARE
PACKED TOGETHER, BUT NOT
AS TIGHTLY AS IN SOLID.
THERE A FEW GAPS HERE AND
THERE SO MOLECULES CAN
ROLL OVER EACH OTHER
(FLOW)
NO DEFINITE SHAPE
MOLECULES ARE FAR APART
OR VOLUME. USES UP AND MOVING RAPIDLY
ENTIRE 3DIMENSIIONAL SPACE
OF CONTAINER
A PHASE CHANGE IS A PHYSICAL
CHANGE.
FOR EXAMPLE, MELTING, BOILING,
FREEZING, CONDENSATION.
YOU ARE NOT CHANGING CHEMICAL
COMPOSITION – NO CHEMICAL BONDS
ARE BROKEN AND NO CHEMICAL BONDS
ARE FORMED.
WE USE CHEMICAL SYMBOLS TO
REPRESENT ATOMS OF DIFFERENT
ELEMENTS. FOR EXAMPLE,
H FOR HYDROGEN
Na FOR SODIUM
Cl FOR CHLORINE
WE USE COMBINATIONS OF SYMBOLS,
FORMULAS, TO REPRESENT MOLECULES.
A MOLECULE IS THE SMALLEST UNIT OF A
COMPOUND – IT IS TWO OR MORE ATOMS
CHEMICALY COMBINED (HELD TOGETHER BY
CHEMICAL BONDS).
EXAMPLES OF FORMULAS:
H2O – WATER – THIS TELLS US THAT FOR
EVERY MOLECULE OF WATER, WE HAVE
TWO ATOMS OF HYDROGEN AND ONE OF
OXYGEN.
THE SUBSCRIPT AFTER THE SYMBOL TELLS
US HOW MANY ATOMS OF THAT ELEMENT
ARE PRESENT IN THE MOLECULE.
OTHER EXAMPLES:
CH4
METHANE (NATURAL GAS)
C6H12O6 GLUCOSE (BLOOD SUGAR)
NaCl
C10H14N2
SODIUM CHLORIDE (TABLE SALT)
NICOTINE
THERE ARE OTHER WAYS OF REPRESENTING
MOLECULES. THESE ARE SIMPLE FORMULAS
AND DO NOT TELL US HOW THE ATOMS ARE
JOINED.
IF YOU PUT A NUMBER IN FRONT OF A
FORMULA, THAT TELLS YOU HOW MANY
MOLECULES YOU HAVE. FOR EXAMPLE:
2H2O
- TWO MOLECULES OF WATER
THE TWO WOULD MULTIPLY EVERYTHING
IN THE FORMULA BY TWO.
YOU WOULD HAVE A TOTAL OF 4
HYDROGENS AND 2 OXYGENS.
THERE ARE SEVERAL DIFFERENT KINDS OF
FORMULAS.
STRUCTURAL FORMULAS SHOW HOW THE
ATOMS ARE ARRANGED.
WATER
STRUCTURAL
FORMULA
WATER SPACE FILLING MODEL,
SHOWING ELECTRON CLOUDS
CHEMISTS USE FORMULAS IN
EQUATIONS TO SHOW CHEMICAL
REACTIONS:
CH4 + 2O2  2H2O + CO2
THE EQUATION TELLS US THAT ONE
MOLECULE OF METHANE WILL REACT
WITH 2 MOLECULES OF OXYGEN TO
YIELD 2 MOLECULES OF WATER AND
ONE MOLECULE OF CARBON DIOXIDE.
THE NUMBERS OF ATOMS OF EACH TYPE
WILL BE THE SAME OF BOTH SIDES OF
THE EQUATION.