2. Greek philosopher Democritus
proposed that all matter, “ the stuff”
that makes us the world around us, is
actually composed of tiny, invisible
particles.
10. The atom is mostly
empty space. Its mass
is concentrated in the
nucleus. (Nuclear
Model)
The protons and
neutrons are particles
inside the nucleus.
He proposed the atomic
model which is called
nuclear atom.
The nucleus is tiny and
densely packed
compared with the
atom as a whole.
11. a Danish physicist
who developed the
Bohr model of the
atom and the
principles of corre
spondence and
complementarity.
He and Werner He
isenberg developed
the “Copenhagen
interpretation” of
quantum theory.
12. Bohr model shows the atom as a
small, positively charged nucleus
surrounded by orbiting electrons.
He discovered that electrons travel
in separate orbits around the nucleus
and that the number of electrons in
the outer orbit determines the
properties of an element.
13. The chemical element bohrium (Bh),
No. 107 on the Periodic Table of the
Elements, is named for him.
The atom is like a solar system. Its
mass is concentrated in the nucleus
in circular orbits.
Each electron carries discrete
amount of energy and does lose any
energy as long as it stays in its given
orbit.
14. Electron that has
received enough
energy can jump to a
higher energy orbit.
Upon return to a
lower energy orbit,
energy is emitted in
the form of light.
The energy of the
light emitted is
equal to the energy
of the two orbits
involved in the
transition.
15. Wilhelm Roentgen
materials used as anodes in vacuum
tubes gave off highly penetrating
radiations, which is like light in some
properties are what we know as x-rays.
X-rays pass through paper, wood, light
metals like aluminum and even human
flesh.
X-rays can be completely stopped by a
thin layer of metals such as platinum,
gold, or lead and by any human bones.
16. At the end of 1895, Wilhelm Röntgen
discovered X rays. Becquerel learned
that the X rays issued from the area
of a glass vacuum tube made
fluorescent when struck by a beam of
cathode rays.
He undertook to investigate whether
there was some fundamental connection
between this invisible radiation and
visible light such that all luminescent
materials, however stimulated, would
also yield X rays.
17. To test this hypothesis, he placed
phosphorescent crystals upon a photographic
plate that had been wrapped in opaque paper
so that only a penetrating radiation could
reach the emulsion.
He exposed his experimental arrangement to
sunlight for several hours, thereby exciting
the crystals in the customary manner. Upon
development, the photographic plate revealed
silhouettes of the mineral samples, and, in
subsequent experiments, the image of a coin
or metal cutout interposed between the
crystal and paper wrapping.
18.
19. Marie and Pierre Curie
Marie described the
behaviour of uranium
and thorium as
radioactivity.
Also, she was the first
to study radioactivity/
20. Marie Curie discovered two new
elements: radium and polonium. We
now know these are inevitable by
products of uranium.
Science tells us, for example, that all
material things are made up of tiny
atoms. The atoms found in most
substances are remarkably stable,
but in the case of radioactive
materials, the atoms are unstable.
Editor's Notes
Radioactivity is the process in which unstable atomic nuclei spontaneously decompose to form nuclei with a higher stability by the release of energetic sub atomic particles.
Becquerel reported this discovery to the Académie des Sciences at its session on February 24, 1896, noting that certain salts of uranium were particularly active.
