Download Historical Development of atomic theory

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First Day: chemistry – Introduction to chemistry
Chemistry is the study of MATTER, including the composition (what
atoms are present), structure (how those atoms are arranged –angles
between them) and behavior (the “reactivity”).
Matter is anything that has mass and volume.
 Mass = the amount of “matter”/atoms in an object.
 Volume = the amount of space taken up
The atom’s composition and structure determine behavior.
Atoms give matter mass and volume…therefore, atoms (while small,
have mass & volume)
Microscopic…………………………………………………….Macroscopic
Atoms
molecules
mixtures
Properties of the substances
Physical & chemical
Elements - The smallest part of matter that cannot be further
subdivided without changing its identity.
Elements are made of atoms. (atoms are the fundamental parts of
elements)
1. Historical Development of the Atom:
2. Historical journey of atomic theory:
Democratis – philosopher, viewed matter like a beach; believed
matter could be made of an “ultra structure” like the
sand particles that cumulatively add up to the
beach… atoms are the smallest part of matter.
Democratis called the particle “atomos”, meaning
indivisible.
Dalton’s Atomic Theory: (explore the left margin menu at the website)
1. Atoms of the same element are identical; atoms of different
elements are different.
2. Atoms are solid, indivisible particles
3. Atoms can combine in whole number ratios to form compounds
4. The compounds can be separated using chemical reactions,
which may cause the atoms to separate or recombine.
JJ Thomson – Cathode ray tube = discovery of electrons
Proposed the plum pudding model
JJ Thomson: atoms are made of a cloud of positive and negative charges distributed
among each other, like plums in pudding (“plum pudding model”)
Rutherford:
** click on the tutorial to the right of the Rutherford icon
The atom is made of an area of a dense, positive charge, called the nucleus. Surrounding
the nucleus is a cloud of negatively charged electrons, spread out, creating mostly empty
space.
The GOLD FOIL EXPERIMENT!! Animation
Observations/Conclusion
1. More than 99% alpha particle go straight through the gold foil. (=atom is mostly empty
space.)
2. HOWEVER, deflections DO OCCUR…so something is changing the direction of the alpha
particles. (like charges repel…(+) alpha particles are repelled by a (+) area = dense,
positive nucleus)
BOHR’S Theory of the atom:
Bohr Model of the atom:
Bohr Model: the electron orbiting the nucleus moves only in certain orbits, having in each a
certain "quantized" energy.
Modern Atomic structure:
Source: http://www.jlab.org/news/releases/2004/04atom.html
Nucleus
“made of positive protons and neutral neutrons”…
“scientists were already describing the nucleus as a conglomeration of indivisible, ball-like
protons and neutrons”
nuclear physicists still use a slightly modified version of this seven-decades-old view of the
nucleus for interpreting data from today’s cutting edge experiments.
the first tool for describing the nucleus in terms of the most basic building blocks of everyday
matter: quarks and gluons.
Quarks were first theorized forty years ago, followed by gluons about half a decade later.
Three quarks and a host of gluons, so-called because they glue quarks together, are found in
each proton and neutron. The nucleus, in turn, is comprised of one or more protons and may
also contain neutrons.
The paper, “Quark Structure and Nuclear Effective Forces,” was published in the September
24 issue of Physical Review Letters.
Think of protons and neutrons (collectively called nucleons) as squirmy bags containing quarks and
gluons. A bag’s shape at any one moment in time depends on its environment. Bags found inside a
nucleus are going to look and act differently from those that roam free. That’s partly because the quarks
inside the squirmy bags are interacting with the quarks inside other bags in the nucleus by exchanging
particles called mesons. Each time a meson is exchanged, the structure of these squirmy bags, or
nucleons, is changed.
“So we don’t see the nucleon as a free proton or neutron with a definite shape, we see it as a cluster of
quarks whose structure is just delicately altered by being placed in the nucleus,” Thomas explains. These
quark-quark interactions via the exchange of mesons generate the forces between nucleons that keeps
the nucleus intact. Thomas and Guichon took this model of interactions, called the Quark-Meson
Coupling Model, and calculated the forces between the nucleons due to the quark-quark interactions.
…deeper, modern theories..
Source:
http://www.phys.ufl.edu/~acosta/phy3101/quarks/img008.gif
FUN WAY TO ASSESS YOUR UNDERSTANDING OF ATOMIC STRUCTURE AND THE HISTORICAL
DEVELOPMENT OF OUR CURRENT THEORY.
Enjoy!