10
R. N. Mohapatra
(a) Everything is composed of atoms, which are the indivisible building blocks
of matter and cannot be destroyed;
(b) All atoms of an element are identical;
(c) The atoms of different elements vary in size and mass;
(d) Compounds are produced through different whole-number combinations
of atoms;
(e) A chemical reaction results in the rearrangement of atoms in the reactant
and product compounds.
All of the above conjectures were eventually verified.
Rutherford’s model made clear what was going on inside the atom, and combined with Thompson’s 1897 discovery of the electron, the picture emerged
that the center of the atom had all the mass and was called the nucleus. The
electrons in their incredible lightness were simply floating around the nucleus.
How they were floating inside the atom came only to be understood with
the proposal of Niels Bohr, who was trying to understand the observed light
emanating from hydrogen atoms. This eventually led to the foundation of a
new field called quantum mechanics, which has far reaching conceptual as well
as technical implications (e.g., from laser scanners in the grocery stores to an
MRI machine in the hospital, to name just two).
Born in Copenhagen in 1885, Bohr was interested in physics from his
very early days. He received his Ph.D. in 1911, in Denmark, working on the
electron theory of metals. Electrons were the fascination of the physicists in
those days since their discovery by J. J. Thompson. After getting his Ph.D.,
Bohr went to work in the group of J. J. Thompson in 1912. Thompson was
not very impressed by Bohr. So Bohr went to join the group of Thompson’s
former colleague Ernest Rutherford in Manchester. Rutherford’s findings had
overturned the “plum pudding” model of Thompson for the atom and he
had already received his Nobel Prize in chemistry in 1908. While Rutherford’s
theory that the central part of an atom was the nucleus and had almost the
entire weight of the atom and the electrons were swarming around it only
to make it electrically neutral, there was a puzzle that was brewing with the
model. In Rutherford’s model, all electrons would eventually spiral towards
the nucleus of positive charges under the attractive electric force and emit light
which would be a continuous band of colors (or frequencies; each color goes
with a frequency of the vibration of the electromagnetic wave).
Scientists had, however, found that light emitted by atoms, such as hydrogen, did not have continuous frequency (or color) as predicted by Rutherford
model. Rather, it was found that only when objects are hot do they give out
light in all mixed colors or continuous colors. But at colder temperatures, they
R. N. Mohapatra
(a) Everything is composed of atoms, which are the indivisible building blocks
of matter and cannot be destroyed;
(b) All atoms of an element are identical;
(c) The atoms of different elements vary in size and mass;
(d) Compounds are produced through different whole-number combinations
of atoms;
(e) A chemical reaction results in the rearrangement of atoms in the reactant
and product compounds.
All of the above conjectures were eventually verified.
Rutherford’s model made clear what was going on inside the atom, and combined with Thompson’s 1897 discovery of the electron, the picture emerged
that the center of the atom had all the mass and was called the nucleus. The
electrons in their incredible lightness were simply floating around the nucleus.
How they were floating inside the atom came only to be understood with
the proposal of Niels Bohr, who was trying to understand the observed light
emanating from hydrogen atoms. This eventually led to the foundation of a
new field called quantum mechanics, which has far reaching conceptual as well
as technical implications (e.g., from laser scanners in the grocery stores to an
MRI machine in the hospital, to name just two).
Born in Copenhagen in 1885, Bohr was interested in physics from his
very early days. He received his Ph.D. in 1911, in Denmark, working on the
electron theory of metals. Electrons were the fascination of the physicists in
those days since their discovery by J. J. Thompson. After getting his Ph.D.,
Bohr went to work in the group of J. J. Thompson in 1912. Thompson was
not very impressed by Bohr. So Bohr went to join the group of Thompson’s
former colleague Ernest Rutherford in Manchester. Rutherford’s findings had
overturned the “plum pudding” model of Thompson for the atom and he
had already received his Nobel Prize in chemistry in 1908. While Rutherford’s
theory that the central part of an atom was the nucleus and had almost the
entire weight of the atom and the electrons were swarming around it only
to make it electrically neutral, there was a puzzle that was brewing with the
model. In Rutherford’s model, all electrons would eventually spiral towards
the nucleus of positive charges under the attractive electric force and emit light
which would be a continuous band of colors (or frequencies; each color goes
with a frequency of the vibration of the electromagnetic wave).
Scientists had, however, found that light emitted by atoms, such as hydrogen, did not have continuous frequency (or color) as predicted by Rutherford
model. Rather, it was found that only when objects are hot do they give out
light in all mixed colors or continuous colors. But at colder temperatures, they