Transcript Atomic theory

Atomic
Theory
Atomic Theory
As early as 400 BC, Greek
philosophers proposed the atomic
theory.
In 1808, John Dalton, an English
chemist and physicist, published an
atomic theory.
1. Each element is composed of
extremely small particles called
atoms.
Atomic Theory continued
2. All atoms of a given element are
identical
3. Atoms of different elements have
different properties, including mass
and chemical reactivity.
4. Atoms are not changed by chemical
reactions, but merely rearranged
into different compounds.
Atomic Theory continued
5. Compounds are formed when
atoms of more than one element
combine.
6. A compound is defined by the
number, type (element), and
proportion of the constituent
atoms.
Over time, new models have been
created and the theory has been
expanded and updated.
Atom Models
• In a famous experiment using alpha
particles and gold foil, Ernest
Rutherford discovered that the atom
was mostly empty space.
• Niels Bohr developed a model of the
atom in which electrons move around
the nucleus in fixed orbits and have a
set amount of energy. We often use
this model when learning about
atoms.
Current Model of the Atoms
Erwin Schrodinger, and Austrian
physicist, developed the quantum
mechanical model of the atom. We
call it the electron cloud model
because it cannot be described in
words or pictures. The cloud
represents the probability of
electron position.
The Neutron
In 1932, James Chadwick discovered
the neutron which explain the missing
mass in an atoms nucleus.
Many new technological
developments have come about as a
result of these discoveries. The late
20th century has become known as the
“atomic age”.