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Modelo Atómico deBohr.

FUNDAMENTAL CONCEPTS OF

QUANTUM PHYSICS

F!ic" III. #P $ %'

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Early Models of the Atom

It was known that atoms

were electrically neutral, but

that they could become

charged, implying that there

were positive and negative

charges and that some of

them could be removed.One popular atomic model

was the “plumpudding!

model"

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Early Models of the Atom

#his model had the atom consisting of a bulk

positive charge, with negative electrons buried

throughout.

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Early Models of the Atom

$utherford did an e%periment that showed that

the positively charged nucleus must be

e%tremely small compared to the rest of theatom. &e scattered alpha particles ' helium

nuclei ' from a metal foil and observed the

scattering angle. &e found that some of the

angles were far larger than the plumpudding

model would allow.

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Early Models of the Atom

#he only way to

account for the

large angles was to

assume that all thepositive charge

was contained

within a tiny

volume ' now we

know that the

radius of the

nucleus is ()(****

that of the atom.

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+.(* Early Models of the Atom

#herefore, $utherford-s

model of the atom is mostly

empty space"

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+.(( Atomic pectra" /ey to the tructure

of the Atom

A very thin gas heated in

a discharge tube emits

light only at

characteristic

fre0uencies.

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Atomic pectra" /ey to the tructure of the

Atom

An atomic spectrum is a line spectrum ' only certain

fre0uencies appear. If white light passes through such a

gas, it absorbs at those same fre0uencies.

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Atomic pectra" /ey to the tructure of the

Atom

#he wavelengths of electrons emitted from

hydrogen have a regular pattern"

1+23

#his is called the 4almer series.  R is the

$ydberg constant"

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Atomic pectra" /ey to the tructure of the

Atom

Other series include the 5yman series"

And the 6aschen series"

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Atomic pectra" /ey to the tructure of the

Atom

A portion of the complete spectrum of hydrogen

is shown here. #he lines cannot be e%plained by

the $utherford theory.

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#he 4ohr Atom

4ohr proposed that the possible energy states for atomic

electrons were 0uanti7ed ' only certain values were

possible. #hen the spectrum could be e%plained as

transitions from one level to another.

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#he 4ohr Atom

4ohr found that the angular momentum

was 0uanti7ed"

1+((3

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#he 4ohr Atom

An electron is held in orbit by the 8oulomb force"

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#he 4ohr Atom

9sing the 8oulomb force, we can calculate the

radii of the orbits"

1+(+3

1+(:3

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#he 4ohr Atom

#he lowest

energy level iscalled the ground

state; the others

are e%cited

states.

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#he 4ohr Atom

#he correspondence principle applies here as

well ' when the differences between 0uantumlevels are small compared to the energies, they

should be imperceptible.