Poetry of Physics and the Physics of Poetry

166 The Poetry of Physics and The Physics of Poetry

electrons floated in a spherical blob of positive charge with a radius of
approximately 10-8 cm. They, therefore, expected that the alpha particle
would pass through the atom without scattering very much because the
electrons were too light to affect the alpha particles very much and
because the positive charge was spread out over the whole atom. The
alpha particle was expected to be only nominally scattered from its
original path.

The Structure of the Atom 159

electrons were too light to affect the alpha particles very much and

because the positive charge was spread out over the whole atom. The

alpha particle was expected to be only nominally scattered from its

original path.

Fig. 17.3

Imagine what a surprise it must have been for Rutherford and his co -

workers when they discovered that a number of alpha particles suffered

considerable deflections and, in fact, some alpha particles had actually

been scattered completely into the backwards direction, i.e., scattered

back into the direction from which they originally came. The observed

scattering of the alpha particles could only have been caused by the

positive charge of the nucleus since the electrons do not have enough

mass to scatter the alpha rays very effectively. But, if the positive charge

of the nucleus were responsible for the large angle scattering of the alpha

particles, then, the positive charge had to be concentrated into a

considerably smaller space as is illustrated in Fig. 17.1. In fact,

Rutherford showed that the positive charge had to be concentrated in a

nucleus with a radius of less than 10-12 cm. The picture of the atom

completely changed overnight. The miniature solar system atom came

back into favour. The atom now consisted of a nucleus, which contains

all of the positive charge in a sphere less than 10-12 cm in radius. (It is

now known that the radii of nuclei vary from 1 to 7 x 10-13 cm.) The

electron circles the nucleus with an orbit whose radius is of the order of

10 -8 cm. Most of the atom therefore consists of empty space. This was

the only picture of the atom consistent with the result of Rutherford's

experiment.

Fig. 17.3

Imagine what a surprise it must have been for Rutherford and his co-
workers when they discovered that a number of alpha particles suffered
considerable deflections and, in fact, some alpha particles had actually
been scattered completely into the backwards direction, i.e., scattered
back into the direction from which they originally came. The observed
scattering of the alpha particles could only have been caused by the
positive charge of the nucleus since the electrons do not have enough
mass to scatter the alpha rays very effectively. But, if the positive charge
of the nucleus were responsible for the large angle scattering of the alpha
particles, then, the positive charge had to be concentrated into a
considerably smaller space as is illustrated in Fig. 17.1. In fact,
Rutherford showed that the positive charge had to be concentrated in a
nucleus with a radius of less than 10-12 cm. The picture of the atom
completely changed overnight. The miniature solar system atom came
back into favour. The atom now consisted of a nucleus, which contains
all of the positive charge in a sphere less than 10-12 cm in radius. (It is
now known that the radii of nuclei vary from 1 to 7 × 10-13 cm.) The
electron circles the nucleus with an orbit whose radius is of the order of