Download Atomic Structure

Atomic Structure
Early Models of the Atom
• Democritus (460 – 370 BCE)
• Among first to suggest existence of atoms
• Believed atoms were indivisible and
indestructible
• John Dalton (1766-1844)
• Used experimental methods to observe atoms
• Studied the ratios in which elements combine
in chemical reactions
• Formulated an atomic theory
Dalton’s Atomic Theory
I.
All elements are composed of tiny indivisible particles
called atoms
II. Atoms of the same element are identical. The atoms
of any one element are different from those of any
other element.
III. Atoms of different elements can physically mix
together or can chemically combine in simple whole
number ratios to form compounds
IV. Chemical reactions occur when atoms are separated,
joined, or rearranged. Atoms of one element are
never changed into atoms of another.
Checkpoint:
What happens to atoms in chemical reactions
according to Dalton?
JJ Thomson (1856-1940)
• Discovered the electron
as a negatively charged
subatomic particle
• Performed experiments
that involved passing
electric current through
gases at low pressure (a
cathode ray tube) and
used a magnet to show
particles with a charge
Thomson Model
• Negative electrons embedded in a sphere of
positive charge
• “plum-pudding”
Ernest Rutherford (1871-1937)
• Student of Thomson
• Conducted the famous “goldfoil experiment”
• Discovered the nucleus as a
dense center to the atom
• Electrons move around the
nucleus
Niels Bohr (1885-1962)
• Student of Rutherford
• Electrons moved in fixed
circular paths around the
nucleus
• Each path was dependent upon
the energy of the electron (the
energy needed to move one
electron from one energy level
to the next is called a
“quantum”)
Erwin Shrödinger (1887-1961)
• Focused his attention on the
energy of electrons
• Found electrons do not travel in
fixed paths, but are randomly
moving in certain areas around
the nucleus
• The quantum-mechanical model
(electron-cloud model) is the
current one we use today.
– Predicts how likely an atom can be
found in a certain location of the
electron-cloud
Today’s model
• Electron-Cloud model/quantum-mechanical
model
• Nucleus: dense center with protons and
neutrons
• Electrons: moving randomly and rapidly
around the nucleus in no fixed path but rather
in probable areas.
Left Page Activity
• On a left page, you are going to create a
timeline of the atom. Make sure to include
the author of the model, a description, and a
picture of each.