|Section 1.3 Page
||Empedocles' and Democritus' atomic models are
not scientific models because they were not based on observations obtained
through experimental. Rather, their models were based on though experiments.
||Dalton's atomic model consists of the following
|• Matter consists of definite particles called
• Each element is made up of its own type of atom.
• Atoms of different elements have different properties.
• Atoms of two or more elements can combine in constant ratios to form new substances.
• Atoms cannot be created, destroyed, or subdivided in a chemical change.
||a) Ernest Rutherford
|b) Ernest Rutherford
|c) John Dalton
|d) Ernest Rutherford
||a) The raisins represent the negatively charged
electrons in the atom.
|b) The bun represents the atom's positively
||a) Democritus' model is the result of a thought
experiment. His model only described the atom as an divisible particle.
Dalton's model is a more detailed description of the atom that includes
some of its physical properties. Dalton's model provided empirical
support to Democritus' idea.
|b) the model of the atom was slow to evolve
for three reasons. First, the technology available for probing the
atom was limited. Second, until several hundred years ago, there were
few people of independent means who were also interested in science as a
hobby, and even fewer who were specifically interests in probing the atom.
third, it took many years for the scientific method to evolve. The
alchemists, who lived during the Middle Ages, were the first group of people
to record methodical observations with the purpose of answering a question.
||a) nucleus: the positively charged
centre of the atom
|b) proton: a positively charged subatomic
particle found in the nucleus of the atom
|c) electron: a negatively charged subatomic
particle found in orbit around the nucleus of the atom
|d) neutron: a subatomic particle with no
charge found in the nucleus of the atom
||a) Scientific knowledge is tentative because
current models and theories are subject to change as new technology allows
us to gather more information. The atomic model is an excellent example
of the tentative nature of science. The atom has evolved from Democritus'
model of an indivisible particle to the current model of a positively charged
centre containing protons and neutrons, with electrons in the space surrounding
it. electron behaviour is currently describe using quantum mechanics.
|b) As new technology is developed, scientists
can further probe the atom. Shortly after cathode ray tubes were invented,
J.J. Thomson proposed that atoms contain negatively charged particles. Without
the cathode ray tube, electrons may not have been discovered.
|c) Each new generation of scientists' builds
on the work of previous generation of scientists. For example, Chadwick
built on Rutherford's model and proposed the presence of neutrons in the
nucleus, in addition to protons.