Atomic spectra (English)

4-2: The Atomic Spectra

The lights from discharge tubes

or arcs across

various kinds of electrodes

with a high voltage potential

being applied

represent line spectra

which consist

of a numbers of bright sharp lines

characteristic of the gases

involved in the tube

or the matters of the electrodes.

Some examples are shown

in the pictures

below.

Examples of Atomic Spectra

The sun light has

a continuous spectrum,

in which there are

some absorption lines

named the Fraunhofer lines

of which detailed explanations

are omitted here.

The spectra of hydrogen

and mercury

show some characteristic lines,

but the pictures here

are not so good

to look them clearly.

[Balmer's Formula]

The group of lines

of the hydrogen spectrum

named the Balmer series

which are observed

in the part from visible to

ultraviolet region

is shown in

the following picture.

(Other series

than the Balmer one,

e.g. the Lymann, Paschen

and Brackett series,

are found in the hydrogen

spectrum as well.)

A line spectra of hydrogen atom

(the Balmer series)

A high school teacher,

J. J. Balmer

(Switzerland, 1825 - 98)

discovered in 1885 that

the wavelengths of the spectral lines, , , and ,

in the Balmer series

shown

in the above picture

are respectively written

and these are represented

by a simple formula

This is called

Balmer's formula.

It has been confirmed

that the other lines

in the Balmer series

than the above , ,

and

also obey Balmer's

formula mentioned above.

[Rydberg's Formula]

In 1890,

Rydberg (Sweden)

found a very simple formula

which

can represent

the wavelengths ,

not only in the

hydrogen spectrum

but also in the spectra

of alkali atoms.

This is

Rydberg's formula

where m

and n are integers,

and a and b

are different

for each series of spectra

but constant within a series.

The constant R

is called the

Rydberg constant

whose value was obtained

from the experimental data

for hydrogen as

Balmer's formula

is one of the special cases in

Rydberg's formula.

Putting

a = b = 0 and

m = 2

in Rydberg's formula,

we can obtain

which is equivalent

to Balmer's formula.

We cannot explain these Balmer's and Rydberg's formulae with the classical theory.

At this point people

necessitated

making a big jump

to a new revolutionary theory.

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