The History of the AtomThe History of the AtomPart 1 – The concept of the AtomPart 1 – The concept of the Atom

A long time ago, in a galaxy A long time ago, in a galaxy country far, far awaycountry far, far awayThere were two There were two philosophersphilosophers

One was One was DemocritusDemocritus Lived in Lived in Ancient GreeceAncient Greece on on

the island of the island of SicilySicily First to use the term First to use the term atomatom

((atomosatomos meaning indivisible) meaning indivisible) Described the atom by Described the atom by

mathematicsmathematics of the day (His of the day (His peer was peer was PythagorasPythagoras))

Atom was described as the Atom was described as the smallestsmallest part of a material part of a material

There were There were rock atoms, hair rock atoms, hair atoms, etc.atoms, etc.

Democritus’s atom would have Democritus’s atom would have looked like this:looked like this:

SolidSolid and and IndestructibleIndestructible

No No electronselectrons No No nucleusnucleus No No protonsprotons No No neutronsneutrons No No ExperimentsExperiments to to

support his ideassupport his ideas

The other was The other was AristotleAristotle

He lived in the heart of He lived in the heart of Greece (Athens)Greece (Athens)

Defined matter as composed Defined matter as composed of of hot, cold, wet and dryhot, cold, wet and dry

These properties related to These properties related to fire, air, water, and earthfire, air, water, and earth

Everything differed by the Everything differed by the percentagespercentages of each that of each that composed the objectcomposed the object

And the winner was:And the winner was:

AristotleAristotle And set chemistry And set chemistry

back about back about 20002000 yearsyears

Chemistry didn’t make Chemistry didn’t make a come back until the a come back until the RenaissanceRenaissance

Antoine LavoisierAntoine Lavoisier FrenchmanFrenchman in the late 1700s in the late 1700s Was working with Was working with gasesgases He discovered that the amount He discovered that the amount

of mass that one of mass that one startedstarted with with was equal to the amount of was equal to the amount of mass that one mass that one ended withended with – – Law of Law of conservationconservation of of massmass..

Also discovered that Also discovered that oxygenoxygen caused things to burncaused things to burn

Some call him the Some call him the Father of Father of ChemistryChemistry

Joseph ProustJoseph Proust Another Another FrenchmanFrenchman a few a few

years after Lavoisieryears after Lavoisier Proposed Law of Proposed Law of Definite Definite

ProportionsProportions Roughly stated: a chemical Roughly stated: a chemical

could have only could have only oneone ratio of ratio of atoms within it.atoms within it.

In other words, a compound In other words, a compound will always have the will always have the samesame elements in the elements in the samesame ratio ratio

Water has to be Water has to be HH22OO and and not not HOHO or or HOHO22

John DaltonJohn Dalton Took his own Took his own experimentsexperiments

and those of others to and those of others to write a write a paperpaper, which later , which later became known as the became known as the Modern Atomic TheoryModern Atomic Theory

It gave a It gave a compilationcompilation of the of the information at the time and information at the time and allowed other scientist to allowed other scientist to testtest his ideas. his ideas.

Dalton's Atomic TheoryDalton's Atomic Theory1)1) All matter is composed of All matter is composed of extremely smallextremely small

particles called atoms, which cannot be particles called atoms, which cannot be subdivided, created,subdivided, created, or or destroyeddestroyed..

2)2) Atoms of a given element are Atoms of a given element are identicalidentical in their in their physicalphysical and and chemicalchemical properties. properties.

3)3) Atoms of Atoms of differentdifferent elements differ in their elements differ in their physicalphysical and and chemicalchemical properties. properties.

4)4) Atoms of Atoms of differentdifferent elements combine in elements combine in simplesimple, , whole-number ratioswhole-number ratios to form to form compoundscompounds

5)5) In chemical reactions, atoms are In chemical reactions, atoms are combinedcombined, , separatedseparated, or , or rearrangedrearranged but are never but are never created, destroyed,created, destroyed, or or changed.changed.

An Analogy for Dalton’s atomAn Analogy for Dalton’s atom

A small atomic fireball

An atom is small, spherical and the same throughout.

Dalton also gave us the Law of Dalton also gave us the Law of Multiple ProportionsMultiple Proportions

Elements could combine in Elements could combine in differentdifferent ratios ratios to produce to produce differentdifferent compounds compounds

For Example, nitrogen and oxygen can For Example, nitrogen and oxygen can form form NN22O, NO, NOO, NO, NO22,, NN22OO33, N, N22OO44,, and and NN22OO55..

His ideas weren’t His ideas weren’t 100%100% correct, but they gave correct, but they gave scientist a good startscientist a good start

Definite and Multiple Definite and Multiple Proportions – The Math Proportions – The Math

InvolvedInvolvedTypes of problems that can be Types of problems that can be

asked at this point in time.asked at this point in time.

Type One – The Easy TypeType One – The Easy Type

Table salt is composed of sodium and Table salt is composed of sodium and chlorine. Chlorine comprises 60.66% of chlorine. Chlorine comprises 60.66% of the compound, what percentage is the compound, what percentage is sodium?sodium?

39.34%39.34% C, H, and O combine to make CC, H, and O combine to make C22HH66OO22. .

Hydrogen is 9.74% and carbon is 38.70%. Hydrogen is 9.74% and carbon is 38.70%. What percent is oxygen?What percent is oxygen?

51.56%51.56%

Type 2 – You will need a periodic Type 2 – You will need a periodic table for this typetable for this type

The formula of ethylene glycol is CThe formula of ethylene glycol is C22HH66OO22, , what percentage by weight do you have of what percentage by weight do you have of each of the elements?each of the elements?

Step 1 – Calculate the mass of CStep 1 – Calculate the mass of C22HH66OO22, by , by adding the adding the massmass of each of each elementelement:: C = 12.01 g x 2C = 12.01 g x 2 H = 1.01 g x 6H = 1.01 g x 6 O = 16.00 g x 2O = 16.00 g x 2

= 24.02 g= 24.02 g= 6.06 g= 6.06 g= 32.00 g= 32.00 g

62.08 g62.08 g

Type 2 – You will need a periodic Type 2 – You will need a periodic table for this typetable for this type

Step 2 – Divide each elemental mass by Step 2 – Divide each elemental mass by the mass of the compoundthe mass of the compound C = 12.01 g x 2C = 12.01 g x 2 H = 1.01 g x 6H = 1.01 g x 6 O = 16.00 g x 2O = 16.00 g x 2

Step 3 – Multiply by 100Step 3 – Multiply by 100 C = 38.69%; H = 9.76%; O = 51.55%C = 38.69%; H = 9.76%; O = 51.55%

= 24.02 g= 24.02 g= 6.06 g= 6.06 g= 32.00 g= 32.00 g

62.08 g62.08 g 62.08 g62.08 g 62.08 g62.08 g

62.08 g62.08 g

= 0.3869 = 0.3869

= 0.0976 = 0.0976 = 0.5155 = 0.5155

Let’s try this one togetherLet’s try this one together

What percentage by weight do you What percentage by weight do you have of each of the elements if have of each of the elements if you have the formula Alyou have the formula Al22OO33??

Now try the rest of the Now try the rest of the problems with you groupsproblems with you groups

AnswersAnswers1.1. 42.9% C and 57.1% O42.9% C and 57.1% O

2.2. 77.7% Fe and 22.3% O77.7% Fe and 22.3% O

3.3. 2.7% H and 97.3% C2.7% H and 97.3% Cll

4.4. 52.2% C, 13.0 % H, and 34.8% O52.2% C, 13.0 % H, and 34.8% O

5.5. 32.4% Na, 22.6% S, and 45.0% O32.4% Na, 22.6% S, and 45.0% O