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?

PURE SUBSTANCEMIXTURE

Only one kind of atom?

Does it appear uniform throughout?

ELEMENT

MOLECULE

HOMOGENEOUS

HETEROGENEOUS

NOYES

YESNO

YESNO

PHASE MACROSCOPIC VIEW MOLECULAR/ATOMIC VIEW

SOLID

DEFINITE VOLUME AND SHAPE

ATOMS/MOLECULES ARE PACKED TIGHTLY TOGETHER SO THAT THEY CAN’T MOVE AROUND EACH OTHER

LIQUID

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)

GAS

NO DEFINITE SHAPE OR VOLUME. USES UP ENTIRE 3-DIMENSIIONAL SPACE OF CONTAINER

MOLECULES ARE FAR APART AND MOVING RAPIDLY

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 SODIUM CHLORIDE (TABLE SALT)

C10H14N2 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.