Dev Elopement of Atomic Theory

8/14/2019 Dev Elopement of Atomic Theory

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TheThe

DevelopmenDevelopmen

t of Atomict of Atomic

TheoryTheory


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TheoryTheory

Unit 1 ExamUnit 1 Exam

ResultsResults


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Remember our Atomic HistoryRemember our Atomic History

Time LineTime Line

450 BCE - Democritus

First posed idea that

matter is made of

indivisible particles called

atoms

Started with the Greeksthen

nothing for a long


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long,


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long time


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until


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1780s Antoine

Lavoisier

proposed the law of

conservation of mass:

matter is neither

created nor destroyed

1790s Joseph Louis

Proustfound that a compound

always has the same

composition regardless of

where it is found

1770s Ben

FranklinExperimented with

electricity and

labeled the charges

+ and -


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1800s John Dalton

Combined Democritus,

Lavoisier and Prousts

theories into a unified

atomic theory of matter

1890s Henri Becquerel, Marie

and Pierre Curie

Discovered radioactivity and

proved that the atom is not the

smallest unit of matter


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1910s Robert Millikan

Measured the charge on the

electron using the oil can

experiment.

1890s JJ Thomson

Discovered that cathoderays were actually

electrons, the negative

particles Franklin saw


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1910s Henry Moseley

Found that each element hasa unique number of positive

charges (protons) and

therefore atomic number

1900s Ernest Rutherford

shot a particles at a thin goldfoil to discover that most of

the mass of an atom (the

nucleus) takes up very little

space


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Law of Conservation ofLaw of Conservation of

MassMass


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Law of DefiniteLaw of Definite

ProportionsProportions Discovered by a Frenchman, Joseph Proust (1754 1826). Sometimes known as Prousts Law. Each compound has a specific ratio of elements

It is a ratio by mass. Water is always 8 grams of oxygen for each 1 gram

of hydrogen
http://en.wikipedia.org/wiki/Image:Proust_joseph.jpg


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The Law of Multiple ProportionsThe Law of Multiple Proportions


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Say What?Say What?

Water is 8 grams of oxygen per 1 gram ofhydrogen.

Hydrogen Peroxide is 16 grams of oxygen per

gram of 1 hydrogen. The ratio of Oxygen to hydrogen is 16 to 8 or

a 2 to 1 ratio

True because you have to add a whole atom,

you cant add a piece of an atom.


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Daltons AtomicDaltons Atomic

TheoryTheory

Thus, armed with the Law of Conservation of Mass,

The Law of Definite & Multiple ProportionsDaltonoutlined five fundamental postulates about atoms:

1. All matter consists of tiny, indivisible particles,

which Dalton called atoms that cannot be broken downor destroyed.

2. All atoms of a particular element are exactly alike,

but atoms of different elements are different.3. All atoms of different elements are unchangeable and

have different physical and chemical properties.

l iD lt At i


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4. Atoms of elements combine to form"compound atoms" (i.e., molecules) of

compounds in simple whole-number ratios.

5. In chemical reactions, atoms are neither

created nor destroyed, but are only

rearranged.

Daltons AtomicDaltons Atomic

TheoryTheory

Hurray!

Were Saved!

Oh, thank

youDalton!


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Random ThoughtsRandom Thoughts

Using similar reasoning techniques for othercompounds, Dalton prepared the first table of

atomic masses (sometimes called atomic weights

by chemists since masses are obtained by

weighing).

His work paved the way for other scientists such

as Joseph Gay-Lussac (1778 1850) and Amadeo

Avogadro (1776 1856) to continue research thatwill be presented in class when we reach the Gas

Laws Unit.


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Percent CompositionPercent Composition

The percentage by mass of each element in

a compound.

If a sample of water contains 2 grams ofhydrogen to 16 grams of oxygen, the

percent composition of oxygen will always

be approximately 89%, or 16 gramsoxygen/18 grams total. Hydrogen would

account for about 11%.


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The End!The End!

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Dev Elopement of Atomic Theory