Atoms – Building Blocks of Matter Notes - Chapter 3 Atoms – Building Blocks of Matter Notes - Chapter 3

FIRST CHEMICAL REACTION

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 Theory The Atom: From Idea to Theory 400 BC Democritus VS Aristotle 400 BC Democritus VS Aristotle Democritus, an ancient Greek and student of Aristotle, proposed the 1st atomic theory. He said that the world is composed of 2 things: void (empty space) and matter. No one supported him and he had NO experimental evidence to support his idea.

Greek Model  Greek philosopher  Idea of ‘atomos’ –Atomos = ‘indivisible’ –‘Atom’ is derived  No experiments to support idea Democritus’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 Theory  Thought all matter was composed of 4 elements: –Earth (cool, heavy) –Water (wet) –Fire (hot) –Air (light) –Ether (close to heaven) ‘MATTER’ FIRE EARTHAIR WATER Hot Wet Cold 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 were established: 1790’s - Basic laws that were established: Chemist discovered, via improved balances, that when a chemical reaction occurred in a closed space that the mass of the material before the change equaled the mass of the marital after the change. Now known as the Law of Conservation of Mass. Discovered by Antoine Laurent Lavoisier ( ) about 1785.

 The Law of Conservation of Mass states that matter can not be created or destroyed in any chemical reaction  The atoms in the reactants are rearranged to form different substances, but none of the atoms disappear, and no new atoms are formed

Law of Conservation of Mass  Notice the mass before the chemical reaction is the same as the mass after the reaction has occurred.

Ex. Of Law of Conservation of Mass  When 245 grams of potassium chlorate are heated, the potassium chlorate breaks down into 78 grams of potassium, 71 grams of chlorine and some oxygen gas. Find out the mass of oxygen gas formed  Potassium chlorate = potassium + chlorine + oxygen  245g 78g 71g ?  245= x  245= x  X= 245 – 149  X = 96

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

It was also known that the same elements can combined to form more than one compound. Example: carbon monoxide (CO) and carbon dioxide (CO 2 ). This is the Law of Multiple Proportions.

Legos 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 H H2H2 H2H2 O2O2 H 2 O H2OH2O + Atoms can be rearranged into different substances.

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

JOHN DALTON ( ) REVIVES ATOMIC THEORY OF MATTER

Dalton’s Theory  He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles.  Atoms of the same element are exactly alike.  Atoms of different elements are different.  Compounds are formed by the joining of atoms of two or more elements.

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