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Intro to atoms

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Patricia Adams

on 10 October 2017

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Transcript of Intro to atoms

Atomic Theory
What does it say?
It simply states that ATOMS are the building blocks of all MATTER!
*Remember* a compound is a pure substance composed of atoms of two or more elements that are chemically combined!
Observations about compounds and the way that compounds react led to the development of three laws!
Law of Definite Proportions
Law of Multiple Proportions
Law of Conservation of Mass
Law of Definite Proportions
States that two samples of a given compound are made of the SAME elements in exactly the SAME proportions by mass regardless of the SIZES or sources of the samples.
Every sample of Ethylene glycol is composed of three elements:
51.56% Oxygen
38.70% Carbon
9.74% Hydrogen

Law of Conservation of Mass
Mass cannot be created or destroyed, but can only change from one form to another.
Law of Multiple Proportions
States that if TWO or more different compounds are composed of the same two elements, the RATIO of the masses of the second element (which combines with a given mass of the first element) is always a ratio of SMALL NUMBERS.
Who is John Dalton?
John Dalton, an English chemist, meteorologist, and physicist, used the Greek concept of the atom and the three laws we just learned to develop an atomic theory, in 1808.
Dalton's theory contains five principles!!!

1. All MATTER is composed of extremely small PARTICLES called ATOMS, which cannot be subdivided, created, or destroyed.
2. Atoms of a given element are identical in their physical and chemical properties (SIZE, MASS, and other PROPERTIES).
3. Atoms of different elements differ in their physical and chemical properties (SIZE, MASS, and other PROPERTIES).
4. Atoms of different elements combine in SIMPLE, WHOLE-NUMBER RATIOS to form compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged but never CREATED, DESTROYED, or SUBDIVIDED.
You will learn later that data gathered since Dalton's time shows that the not all of these principles are true in ALL cases.
The first appearance of the atomic theory was in 400 BC. DEMOCRITUS, a philosopher, went against the accepted view of the time (namely Aristotle) and developed the theory of "ATOMOS" or indivisible.
The development of
the Atomic Theory

This holds true no matter how much Ethylene we are talking about: 1 liter or 5 liters or more
Compound 1 = 42.9% Carbon and 57.1% Oxygen
Compound 2 = 27.3% Carbon and 72.7% Oxygen

57.1g Oxygen / 42.9g C = 1.33g Oxygen per g C
72.7g Oxygen / 27.3g C = 2.66g Oxygen per g C

Compound 2 / Compound 1 = 2.66 / 1.33 = 2
Masses of Oxygen that combine with Carbon are in a 2:1 ratio.
LEQ: How has the atomic model
changed as scientists learned
more about the structure of
the atom?
Try the problem in your notes:

Phosphorus forms two compounds with Chlorine. IN the first compound 1.000g of Phosphorus is combined with 3.433g of Chlorine. In the second, 2.500g Phosphorus is combined with 14.306g Cl. Are these results consistent with the Law of Multiple Proportions?
You need to memorize these principles (will see in all sorts of places, like the District EOC) :(
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