Is there a basic substance that

everything else is made of?

585 B.C.

THALES of Miletus "Thales assures that water is the principle of

all things; and that God is that Mind which shaped and created all things from water.“- Cicero

Source of all things is WATER

570-526 B.C.ANAXIMENESSource of all things must be AIR or VAPOR

490-430 B.C.EMPEDOCLESMatter is made up of four elements EARTH, WATER, AIR and FIRE

500-428 B.C.ANAXAGORASNature is built up of an infinite number of

minute particles invisible to the eye.

460-370 B.C.DEMOCRITUS1. All matter is composed of

“atomos”, which are bits of matter too small to be seen.

2. There is a void, which is empty space between atoms.

3. Atomos are completely solid.

4. Atomos are homogeneous, with no internal structure.

5. Atomos are different in their sizes and their shapes

384-322 B.C.ARISTOTLERejected the idea of atomism of matterThere is no limit to subdividing matter

The ATOMIC THEORYJohn Dalton 1766-1844

DALTON’s Atomic TheoryATOMExpress idea of indivisibilityTiny indestructible sphere with massDo not change during chemical reactionAtoms of a given element have the exactly

same properties, but atoms of different elements have different properties.

DALTON’s Atomic TheoryEach element is composed of extremely small

particles called atom.

All atoms of a given element are identical; the atoms of different elements are different and have different properties, including different masses.

Atoms of an element are not changed into different types of atoms by chemical reaction; atoms are neither created nor destroyed in a chemical reaction.

Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Each element is composed of extremely small particles called atom.

All atoms of a given element are identical; the atoms of different elements are different and have different properties, including different masses.

Atoms of an element are not changed into different types of atoms by chemical reaction; atoms are neither created nor destroyed in a chemical reaction.

Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number /ratio and kind of atoms.

Exercise

1. When copper was exposed to air and heated, it was found out that the black compound formed has a copper-to-oxygen ratio of 4:1.the experiment was repeated several times and gave the same results. Explain this finding based on Dalton’s atomic theory.

2. A sample of calcium carbonate was mixed with a certain volume of hydrochloric acid, enough to completely react with the calcium carbonate. The container was tightly sealed and the total mass before and after the reaction was found constant. Explain this observation based on Dalton’s atomic theory.

3. It was found that there are two oxides of copper. One is black with a copper-to-oxygen mass ratio of 4:1 and melting point of 1326 C. the other is red with copper-to-oxygen ratio of 8:1 and melting point of 1235 C. explain these observations based on Dalton’s assumptions.

Laws of Chemical Combination

What makes compounds different?

Law of Constant Composition1799 Joseph Prousta chemical compound contains the same

elements in exactly the same proportions (ratios) by mass regardless of the size of the sample or source of the compound

For example, water always consists of oxygen and hydrogen atoms, and it is always 89 percent oxygen by mass and 11 percent hydrogen by mass

Does mass change during a chemical reaction?

Law of Conservation of MassLavoisier heated a measured amount of

mercury to form the red oxide of mercury. He measured the amount of oxygen removed from the jar and the amount of red oxide formed. When the reaction was reversed, he found the original amounts of mercury and oxygen.

Law of Conservation of Mass1744 Antoine Lavoisiermatter can not be created or destroyed in

ordinary chemical or physical changes. the mass of the reactants (starting materials)

equals the mass of the products

2Mg (s) + O2 (g) → 2MgO (s)

48.6 g 32.0 g 80.6 g

Example

10 grams of CaCO3 on heating gave 4.4g of CO2 and 5.6 of CaO. Show that these observations are in agreement with the law of conservation

Law of Multiple Proportions1803 John Dalton

States that when two elements combine to form more than one compound, the masses of one element which combine with a fixed mass of the other element are in ratios of small whole numbers

Example:Carbon monoxide (CO): 12 parts by mass of

carbon combines with 16 parts by mass of oxygen.

Carbon dioxide (CO2): 12 parts by mass of carbon combines with 32 parts by mass of oxygen.

Ratio of the masses of oxygen that combines with a fixed mass of carbon (12 parts) 16: 32 or 1: 2

Water has an oxygen-to-hydrogen mass ratio of 7.9:1.

Hydrogen peroxide, another compound consisting of oxygen and hydrogen, has an oxygen-to-hydrogen mass ratio of 15.8:1.

Ratio of the masses of oxygen that combines with a fixed mass of hydrogen is 7.9: 15.8 or 1: 2

Exercise