Unit 3Unit 3

Atomic TheoryAtomic Theory

Chapter 3Chapter 3

Early BeliefsEarly Beliefs

Ancient Greek, Hindu, and Japanese Ancient Greek, Hindu, and Japanese systems contained 5 elementssystems contained 5 elements

1) Earth1) Earth

2) Air or Wind2) Air or Wind

3) Water3) Water

4) Fire & 4) Fire &

5) Void, Ether, or Heaven5) Void, Ether, or Heaven

Early Beliefs (cont’d)Early Beliefs (cont’d)

Substances (like gold) were combinations Substances (like gold) were combinations of the elements.of the elements.

You can continue to split a substance in You can continue to split a substance in half until you broke it down into the half until you broke it down into the elements.elements.

Elements could be divided in half infinitely.Elements could be divided in half infinitely.

The Ancient GreeksThe Ancient Greeks

Democritus Democritus ((and his teacher Leucippusand his teacher Leucippus)) had an idea that was different: Matter is…had an idea that was different: Matter is… Composed of indivisible parts.Composed of indivisible parts. The parts are called atomos.The parts are called atomos. Properties of matter are due to the size, Properties of matter are due to the size,

shape, and weight of the atomos.shape, and weight of the atomos.

His idea was not popular and was His idea was not popular and was abandoned for over 2,000 years.abandoned for over 2,000 years.

Democritus Democritus (460-370 BCE)(460-370 BCE)

By convention there is By convention there is sweet, by convention sweet, by convention there is bitterness, by there is bitterness, by convention hot and cold, convention hot and cold, by convention color; but by convention color; but in reality there are only in reality there are only atoms and the void.atoms and the void.

Current Research Indicates that Current Research Indicates that your your colorcolor perception is dependent perception is dependent upon the upon the orderorder in which you in which you learned your learned your colorscolors!! Goto: http://bit.ly/1belMUl

Crazy AncientsCrazy Ancients

Since they had no microscopes or precise Since they had no microscopes or precise measuring devices,measuring devices, All experimental work was done crudely.All experimental work was done crudely. Conclusions were mostly derived from Conclusions were mostly derived from

pure thought.pure thought.

This led to some crazy ideas…This led to some crazy ideas…

Like Alchemy.Like Alchemy.

AlchemyAlchemy

Since substances were made up of the Since substances were made up of the same 4 or 5 elements, they could be same 4 or 5 elements, they could be transmuted into other substances by transmuted into other substances by changing the ratios of elements in them.changing the ratios of elements in them.

The race began to change lead into gold.The race began to change lead into gold.

FfffffailureFfffffailure

For eons, alchemists tried and failed, they For eons, alchemists tried and failed, they could never transmute lead into gold.could never transmute lead into gold.

Did have some successes (making colors, Did have some successes (making colors, fire, etc)fire, etc)

It was more of an art.It was more of an art.

And they kept trade secrets.And they kept trade secrets.

The Death of AlchemyThe Death of Alchemy

Many alchemists died…Many alchemists died…

because they swindled a lot of powerful because they swindled a lot of powerful (and rich) people.(and rich) people.

For years, alchemy was a taboo.For years, alchemy was a taboo.

Eventually, a different class of people Eventually, a different class of people emerged.emerged.

They built on the lessons of alchemy.They built on the lessons of alchemy.

Fast ForwardFast Forward

Scientists and the scientific method Scientists and the scientific method emerged.emerged.

In the late 1700’s and early 1800’s, In the late 1700’s and early 1800’s,

Scientists began to notice that certain Scientists began to notice that certain substances combined substances combined

With other substances in specific amounts.With other substances in specific amounts.

Law Abiding ElementsLaw Abiding Elements

The Law of Definite Proportions was declared:The Law of Definite Proportions was declared:

A chemical compound always contains the A chemical compound always contains the same elements in exactly the same same elements in exactly the same proportions by weightproportions by weight

Two samples of same the compound will Two samples of same the compound will always have the exact same percent always have the exact same percent composition of elementscomposition of elements

It is intensive (doesn’t matter how much you It is intensive (doesn’t matter how much you have, the percentage will always be the same!)have, the percentage will always be the same!)

Proportional LegalityProportional Legality

Another law was needed to describe Another law was needed to describe different things made of the same different things made of the same elements…elements…The Law of Multiple Proportions states:The Law of Multiple Proportions states:When two elements combine to form two When two elements combine to form two or more compounds, the mass of one or more compounds, the mass of one element that combines with a given mass element that combines with a given mass of the other is in the ratio of small whole of the other is in the ratio of small whole numbers.numbers.

Huh?!?Huh?!?

In English, the Law of Multiple Proportions:In English, the Law of Multiple Proportions:

When two or more compounds are made When two or more compounds are made up of the same elements, their percent up of the same elements, their percent compositions will always be different.compositions will always be different.

ExampleExample

Water is made up of Water is made up of 88.81% oxygen and 88.81% oxygen and 11.19% hydrogen.11.19% hydrogen.

26.5 g water = 23.5 g O & 3.0 g H26.5 g water = 23.5 g O & 3.0 g H

Hydrogen peroxide is Hydrogen peroxide is 94.07% O and 94.07% O and 5.93% H.5.93% H.

26.5 g H26.5 g H22OO22 = 24.9 g O & 1.6 g H = 24.9 g O & 1.6 g H

Percent CompositionPercent Composition

The make-up of a compound can be The make-up of a compound can be expressed by a percentage of each expressed by a percentage of each element.element.

To calculate percent composition, you To calculate percent composition, you need to know how much of each element it need to know how much of each element it takes to make the compound.takes to make the compound.

Total Weight of ElementTotal Weight of Element

Total Weight of Total Weight of CompoundCompound

PercentPercent

100100==

ExampleExample

If you combine 15.7 g of sodium metal If you combine 15.7 g of sodium metal (Na) with 24.2 g chlorine gas (Cl), you will (Na) with 24.2 g chlorine gas (Cl), you will produce 39.9 g sodium chloride (salt).produce 39.9 g sodium chloride (salt).

What is the % comp for each element?What is the % comp for each element?

%Na = 15.7 / 39.9 * 100 = 39.3%%Na = 15.7 / 39.9 * 100 = 39.3%

%Cl = 24.2 / 39.9 * 100 = 60.7%%Cl = 24.2 / 39.9 * 100 = 60.7%

Total = 39.9 / 39.9 * 100 = 100%Total = 39.9 / 39.9 * 100 = 100%

Total Percent MUST always equal 100%

What goes in…must come outWhat goes in…must come out

Early scientists began to notice that the Early scientists began to notice that the combined weight of the reactants combined weight of the reactants

Is always the same as the combined Is always the same as the combined weight of the products.weight of the products.

We cannot destroy (or create) matter.We cannot destroy (or create) matter.

Conservative MatterConservative Matter

The Law of Conservation of Mass:The Law of Conservation of Mass:

Matter can neither be created nor Matter can neither be created nor destroyed (in a chemical reaction), but destroyed (in a chemical reaction), but only changed from one form to another.only changed from one form to another.

When we react substances, they must When we react substances, they must always be accounted for in the products.always be accounted for in the products.

Conserve This!!!Conserve This!!!

30.0 g iron reacts with 12.9 g oxygen to 30.0 g iron reacts with 12.9 g oxygen to form 42.9 g rust – at 100% yield.form 42.9 g rust – at 100% yield. 30.0 g + 12.9 g = 42.9 g30.0 g + 12.9 g = 42.9 g Rust is 69.9% Fe and 30.1% ORust is 69.9% Fe and 30.1% O

In order to obey the law, 30.0 g iron and In order to obey the law, 30.0 g iron and 12.9 g oxygen 12.9 g oxygen mustmust form 42.9 g of form 42.9 g of something – regardless of yield.something – regardless of yield.

42.9 g go in, 42.9 g must come out.42.9 g go in, 42.9 g must come out.

John Dalton (1766-1844)John Dalton (1766-1844)

English chemist / physicist / English chemist / physicist / meteorologistmeteorologistMany areas of influenceMany areas of influence Colorblindness (he was Colorblindness (he was

colorblind)colorblind) The behavior of gases,The behavior of gases, Interactions of light & heat, Interactions of light & heat,

andand The behavior of chemicals.The behavior of chemicals.

ColorblindnessColorblindness

Before Dalton, no official description of itBefore Dalton, no official description of it

More Blindness…More Blindness…

Dalton’s WorkDalton’s Work

He was very persistent and stubborn.He was very persistent and stubborn.

Accepted his own very crude results over Accepted his own very crude results over better data of others becausebetter data of others because

He’d been fooled before by erroneous He’d been fooled before by erroneous data from others.data from others.

Returning to DemocritusReturning to Democritus

In 1803, Dalton published his “Atomic In 1803, Dalton published his “Atomic Theory”.Theory”.

1) All matter is composed of extremely 1) All matter is composed of extremely small particles called atoms, which cannot small particles called atoms, which cannot be subdivided, created, or destroyed.be subdivided, created, or destroyed.

2) Atoms of a given element are identical 2) Atoms of a given element are identical in their physical and chemical properties.in their physical and chemical properties.

Atomic Theory (cont’d)Atomic Theory (cont’d)

3) Atoms of different elements differ in 3) Atoms of different elements differ in their physical and chemical properties.their physical and chemical properties.

4) Atoms of different elements combine in 4) Atoms of different elements combine in simple, whole number ratios to form simple, whole number ratios to form compounds.compounds.

5) In chemical reactions, atoms are 5) In chemical reactions, atoms are combined, separated, or rearranged but combined, separated, or rearranged but never created, destroyed, or changed.never created, destroyed, or changed.

Atoms ShmatomsAtoms Shmatoms

He was unable to prove He was unable to prove the existence of atoms.the existence of atoms.

Dalton’s work came out Dalton’s work came out in 1803.in 1803.

It wasn’t until 1905 that It wasn’t until 1905 that the existence of atoms the existence of atoms was proven by Albert was proven by Albert Einstein.Einstein.

My paper on My paper on Brownian Brownian MotionMotion proved the existence proved the existence of atoms…it was confusing, of atoms…it was confusing, but not nearly as confusing but not nearly as confusing

as my paper on as my paper on Special Special RelativityRelativity that came out in that came out in

the same year…the same year…

SummarySummary

Law of Definite ProportionsLaw of Definite Proportions Compounds will always have the same Compounds will always have the same

percent composition.percent composition.

Law of Multiple ProportionsLaw of Multiple Proportions Different Compounds made up of the same Different Compounds made up of the same

elements will always have different percent elements will always have different percent compositions.compositions.

Summary (cont’d)Summary (cont’d)

Law of Conservation of MassLaw of Conservation of Mass Total mass of Reactants must equal total Total mass of Reactants must equal total

mass of products.mass of products.

Dalton’s Atomic TheoryDalton’s Atomic Theory1. Matter is composed of atoms.1. Matter is composed of atoms.

2. Atoms of element are identical.2. Atoms of element are identical.

3. Properties of different elements are different.3. Properties of different elements are different.

4. Atoms combine in whole numbers.4. Atoms combine in whole numbers.

5. Cannot create or destroy atoms.5. Cannot create or destroy atoms.