Atoms – Building Atoms – Building Blocks of Matter Blocks of Matter

Notes - Chapter 3 Notes - Chapter 3   

FIRST CHEMICAL REACTION

Who are these men?Who are these men?

In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

The Atom: From Idea to The Atom: From Idea to TheoryTheory

400 BC Democritus VS Aristotle400 BC Democritus VS Aristotle

DemocritusDemocritus,, an ancient Greek and student of an ancient Greek and student of Aristotle, proposed the 1st atomic theory. Aristotle, proposed the 1st atomic theory. He said that the world is composed of 2 He said that the world is composed of 2 things: void (empty space) and matter. No things: void (empty space) and matter. No one supported him and he had NO one supported him and he had NO experimental evidence to support his idea.experimental evidence to support his idea.

Greek ModelGreek Model

Greek philosopherGreek philosopher Idea of ‘atomos’Idea of ‘atomos’

– Atomos = ‘Atomos = ‘indivisibleindivisible’’– ‘‘Atom’ is derived Atom’ is derived

No experiments to support No experiments to support ideaideaDemocritus’s model of atom

No protons, electrons, or neutrons

Solid and INDESTRUCTABLE

Democritus

“To understand the very large,

we must understand the very small.”

Aristotle - Four Element TheoryAristotle - Four Element Theory

Thought all matter was Thought all matter was composed of 4 composed of 4 elements:elements:– Earth (cool, heavy)Earth (cool, heavy)– Water (wet)Water (wet)– Fire (hot)Fire (hot)– Air (light)Air (light)– Ether (close to heaven)Ether (close to heaven)

‘MATTER’

FIRE

EARTHAIR

WATER

Hot

WetCold

Dry

Relation of the four elements and the four qualities

Blend these “elements” in different proportions to get all substances

1790’s - Basic laws that 1790’s - Basic laws that were established:were established:

Chemist discovered, via improved Chemist discovered, via improved balances, that when a chemical reaction balances, that when a chemical reaction occurred in a closed space that the occurred in a closed space that the mass of the material before the change mass of the material before the change equaled the mass of the marital after equaled the mass of the marital after the change. Now known as the the change. Now known as the Law of Law of Conservation of Mass.Conservation of Mass.

Discovered by Antoine Laurent Lavoisier (1743-94) about 1785.

TheThe Law of Conservation of MassLaw of Conservation of Mass states states that matter can not be created or destroyed that matter can not be created or destroyed in any chemical reactionin any chemical reaction

The atoms in the reactants are rearranged The atoms in the reactants are rearranged to form different substances, but none of the to form different substances, but none of the atoms disappear, and no new atoms are atoms disappear, and no new atoms are formedformed

Law of Conservation of MassLaw of Conservation of Mass

Notice the mass before the chemical Notice the mass before the chemical reaction is the same as the mass after the reaction is the same as the mass after the reaction has occurred. reaction has occurred.

Ex. Of Law of Conservation of MassEx. Of Law of Conservation of Mass

When 245 grams of potassium chlorate are heated, the When 245 grams of potassium chlorate are heated, the potassium chlorate breaks down into 78 grams of potassium chlorate breaks down into 78 grams of potassium, 71 grams of chlorine and some oxygen gas. potassium, 71 grams of chlorine and some oxygen gas. Find out the mass of oxygen gas formedFind out the mass of oxygen gas formed

Potassium chlorate = potassium + chlorine + oxygenPotassium chlorate = potassium + chlorine + oxygen 245g 78g 71g ?245g 78g 71g ?

245= 78 + 71 + x245= 78 + 71 + x 245= 149 + x245= 149 + x X= 245 – 149X= 245 – 149 X = 96X = 96

Another realization was that substances Another realization was that substances always contained their elements in the same always contained their elements in the same proportions by mass. For example: for any proportions by mass. For example: for any sample of sodium chloride, the mass of the sample of sodium chloride, the mass of the sample is always 39.34% Na and 60.66% sample is always 39.34% Na and 60.66% Cl. Now known as the Cl. Now known as the Law of Definite Proportions.

It was also known that the same elements can It was also known that the same elements can combined to form more than one compound. combined to form more than one compound. Example: carbon monoxide (CO) and Example: carbon monoxide (CO) and carbon dioxide (COcarbon dioxide (CO22). This is the ). This is the Law of Law of

Multiple ProportionsMultiple Proportions..

Legos are Similar to AtomsLegos are Similar to Atoms

Lego's can be taken apart and built into many different things.

H

H

O

O

O

O

H

H

H

H

H

HH2

H2

O2

H2O

H2O

+

Atoms can be rearranged into different substances.

Dalton’s ModelDalton’s Model

In the early 1800s, In the early 1800s, the English Chemist the English Chemist John John Dalton Dalton performed a performed a number of number of experiments that experiments that eventually led to the eventually led to the acceptance of the acceptance of the idea of atoms.idea of atoms.

JOHN DALTON (1766 - 1844) REVIVES ATOMIC THEORY OF MATTER

Dalton’s TheoryDalton’s Theory

He deduced that all He deduced that all elementselements are composed of are composed of atoms. Atoms are atoms. Atoms are indivisible and indivisible and indestructible particles.indestructible particles.

Atoms of the Atoms of the samesame element element are exactly alike.are exactly alike.

Atoms of Atoms of differentdifferent elements elements are are differentdifferent..

CompoundsCompounds are formed by are formed by the joining of atoms of two the joining of atoms of two or more elements.or more elements.

..

This theory This theory became one became one of the of the foundations of foundations of modern modern chemistry.chemistry.