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 SUBSTANCE MIXTURE Only one kind of atom? Does it appear uniform throughout? ELEMENT MOLECULE HOMOGENEOUS HETEROGENEOUS NO YES NO YES NO

PHASEMACROSCOPIC VIEWMOLECULAR/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: H 2 O – 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: CH 4 METHANE (NATURAL GAS) C 6 H 12 O 6 GLUCOSE (BLOOD SUGAR) NaCl SODIUM CHLORIDE (TABLE SALT) C 10 H 14 N 2 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: 2H 2 O - 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: CH 4 + 2O 2  2H 2 O + CO 2 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.