Rutherford Bohar atomic model

2. • This model of the atom, based on the work of
Rutherford and Bohr, shows electrons circulating
about the nucleus like planets circulating about the
Sun. It can be a useful model for some purposes, but it
does not represent even approximately the structure
of real atoms.

3. • Our goal in this chapter is to understand some of the details of atomic
structure that can be learned from experimental studies of atoms. In
particular, we discuss two types of experiments that are important in
the development of our theory of atomic structure:
• the scattering of charged particles by atoms, which tells us about the
distribution of electric charge in atoms,
• the emission or absorption of radiation by atoms, which tells us about
their excited states.

4. • We use the information obtained from these experiments to develop
an atomic model, which helps us understand and explain the
properties of atoms. A model is usually an oversimplified picture of a
more complex system, which provides some insight into its operation
but may not be sufficiently detailed to explain all of its properties.

5. • Atoms are very small, about 0.1nm (0.1 × 10 −9 m) in radius. Thus any
effort to “see” an atom using visible light (λ = 500nm) is hopeless
owing to diffraction effects. We can make a crude estimate of the
maximum size

6. • Atoms are stable—they do not spontaneously break apart into
smaller pieces or collapse; therefore the internal forces that hold the
atom together must be in equilibrium. This immediately tells us that
the forces that pull the parts of an atom together must be opposed in
someway; otherwise atoms would collapse.

7. • Atoms contain negatively charged electrons, but are electrically
neutral. If we disturb an atom or collection of atoms with sufficient
force, electrons are emitted. We learn this fact from studying the
Compton effect and the photoelectric effect. We also learned that
even though electrons are emitted from the nuclei of atoms in certain
radioactive decay processes, they don’t “exist” in those nuclei but are
manufactured there by some process. Electrons were excluded from
the nucleus based on the uncertainty principle, which forbids emitted
electrons of the energies observed in the laboratory from existing in
the nucleus. The uncertainty principle places no such restriction on
the existence of electrons in a volume as large as an

8. • Atoms emit and absorb electromagnetic radiation. This radiation may
take many forms—visible light (λ ∼ 500 nm), X rays (λ ∼ 1 nm),
ultraviolet rays (λ ∼ 10nm),infrared rays (λ ∼ 0.1 μm),and so forth. In
fact it is from observation of these emitted and absorbed radiations,
which can be measured with great precision

9. • The Thomson model of
the atom. Z electrons are
imbedded in a uniform
sphere of positive charge
Ze and radius R.

19. • Let’s assume that a projectile of positive charge ze is incident on an
atom of radius R that we represent according to the Thomson model
as a uniform sphere of positive charge Ze. The force on the projectile
when it is a distance r from the center of the atom can be computed
using Gauss’s law