Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Atomic Theories
In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which
states that matter is composed of discrete units called atoms
...

English chemist John Dalton (1766-1844) is the scientist credited for proposing the atomic
theory
...

The first was the law of conservation of mass, formulated by Antoine Lavoisier in 1789, which
states that the total mass in a chemical reaction remains constant (that is, the reactants have
the same mass as the products)
...
First proven
by the French chemist Joseph Louis Proust in 1799, this law states that if a compound is broken
down into its constituent elements, then the masses of the constituents will always have the
same proportions, regardless of the quantity or source of the original substance
...
Dalton's theory can
be called modern because it contained statements about atoms that could be tested
experimentally
...
He said:
1
...

3
...

5
...

All atoms of a given element are identical
...

In chemical reactions, atoms combine with or separate from other atoms
...


(By the term combined atoms, Dalton meant the particles that we now call molecules
...
In 1897,
English physicist J
...
Thomson (1856–1940) discovered that atoms are not indivisible
...
One of those parts
is a tiny particle carrying a negative electrical charge, the electron
...
The name comes from a comparison of the atom with
a traditional English plum pudding, in which plums are embedded in pudding, as shown in the
accompanying figure of the evolution of atomic theory
...

Like the Dalton model before it, Thomson's plum-pudding atom was soon put to the test
...
In the period between 1906 and 1908, English chemist and
physicist Ernest Rutherford (1871–1937) studied the effects of bombarding thin gold foil

with alpha particles
...

First, most of the alpha particles traveled right through the foil without being deflected at all
...
Second, a
few of the alpha particles were deflected at very sharp angles
...

According to Rutherford, the conclusion to be drawn from this result was that the positive
charge in an atom must all be packed together in one small region of the atom
...

One part of Rutherford's model—the nucleus—has turned out to be correct
...
The solution to
this dilemma was proposed in a new and brilliant atomic theory in 1913
...
Let's call those places "permitted orbits," something like the orbits that
planets travel in their journey around the Sun
...
The test, of course, was to see if
the Bohr model could survive experiments designed specifically to test it
...
Within a
very short period of time, other scientists were able to report that the Bohr model met all the
tests they were able to devise for it
...

One final problem remained
...
This balance is the only way to be sure that an atom is electrically neutral, which we
know to be the case for all atoms
...
The reason for mass differences, Chadwick
found, was that the nuclei of atoms contain a particle with no electric charge
...
Chadwick's discovery resulted in a model of the atom that is fairly easy to
understand
...
Outside the nucleus are electrons traveling in discrete orbits

---