Chemistry principles, law of definite proportions and law of multiple proportions

2. ELEMENT
 An element is a pure substance that cannot
be separated in to simpler substances by
physical or chemical means

3. ELEMENTS
 The 91 elements abundance of the
elementsOn earth, 91 elements occur
naturally
 There are also several elements that do not
exist naturally but have been developed by
scientists

4. ELEMENTS
 On earth, 91 naturally ocurring elements are
not equally abundant.
 Hydrogen is estimated to makeup
approximately 75% os the mass of the
universe.
 Oxygen and Silicon together comprise almost
75% of the mass of Earth’s crust.

5. ELEMENTS
 Oxygen , Carbon and Hydrogen account for
more than 90% of the human body.
 Francium, it is estimated that there is
probably less than 20 gram in all the Earth’s
crust (the mass of your pencil or pen!)

6. •To separate a
compound into its
elements often
requires external
energy such as
heat or electricity
•Example: Hoffman apparatus
COMPOUNDS

7. •A compound is a combination of two or more
different that are combined chemically
COMPOUNDS

8. •TheThe
properties of aproperties of a
compound arecompound are
different fromdifferent from
those of itsthose of its
componentcomponent
elements.elements.
COMPOUNDS

9. Law of Definite Proportions
 An important characteristic of compounds isAn important characteristic of compounds is
that the elements comprising them combinethat the elements comprising them combine
in definite proportions b y massin definite proportions b y mass
 Regardless of the amount, a compound isRegardless of the amount, a compound is
always composed of the same elements inalways composed of the same elements in
the same proportion by massthe same proportion by mass

10. Law of Definite Proportions

11. Law of Definite Proportions

12. Law of Definite Proportions

13. Law of Multiple Proportions
•Compounds composed of differentCompounds composed of different
elements are obviously differentelements are obviously different
compounds.compounds.
•Can compounds that are composed of theCan compounds that are composed of the
same elements differ fromsame elements differ from each other?each other?

14. Law of Multiple Proportions
States that whenStates that when different compoundsdifferent compounds
are formed by a combination of theare formed by a combination of the
same elements, different masses ofsame elements, different masses of
one element combine with the sameone element combine with the same
relative mass of the other element in arelative mass of the other element in a
ratio of small whole numbersratio of small whole numbers..

15. Law of Multiple Proportions
•Ratios compare the relativeRatios compare the relative amounts ofamounts of
any items or substances.any items or substances.
•The comparison can be expressed usingThe comparison can be expressed using
numbers separated by a colon or as anumbers separated by a colon or as a
fraction.fraction.
•With regard to the law of multipleWith regard to the law of multiple
proportions, ratios express theproportions, ratios express the
relationship of elements in a compoundrelationship of elements in a compound

16. Law of Multiple Proportions
•The two distinct compounds water (HThe two distinct compounds water (H22O)O)
and hydrogen peroxide (Hand hydrogen peroxide (H22OO22) illustrate the) illustrate the
law of multiple proportions.law of multiple proportions.
•Each compound contains the sameEach compound contains the same
elements (hydrogen and oxygen).elements (hydrogen and oxygen).
•Water is composed of two parts hydrogenWater is composed of two parts hydrogen
(the element that is present in the same(the element that is present in the same
amount in both compounds) to one partamount in both compounds) to one part
oxygen (the element that is present inoxygen (the element that is present in
different amounts in both compounds).different amounts in both compounds).

17. Law of Multiple Proportions
•Hydrogen peroxide is composed of twoHydrogen peroxide is composed of two
parts hydrogen and two parts oxygen.parts hydrogen and two parts oxygen.
•Hydrogen peroxide differs from water inHydrogen peroxide differs from water in
that it has twice as much oxygen.that it has twice as much oxygen.
•When we compare the mass of oxygenWhen we compare the mass of oxygen
in hydrogen peroxide to the mass ofin hydrogen peroxide to the mass of
oxygen in water, we get the ratio 2:1oxygen in water, we get the ratio 2:1

19. Law of Multiple Proportions
As the law of multiple proportions states, theAs the law of multiple proportions states, the
different masses of copper that combine withdifferent masses of copper that combine with
a fixed mass of chlorine in the two differenta fixed mass of chlorine in the two different
copper compounds, shown in Figure 3-22,copper compounds, shown in Figure 3-22,
can be expressed as a small whole-numbercan be expressed as a small whole-number
ratio, in this case 2:1.ratio, in this case 2:1.