Notes: Atomic Theory (Ch3, Sec 1 & 2)
An Ancient _________________ Philosopher
Democritus
1.
About ____________
2. Thought that _____________ was composed of ___________
indivisible particles (atomos = ___________________)
3. He called them ______________.
John Dalton’s model
In the 1700’s, improved _________________ and experimentation allowed scientists to
come up with some ____________ laws…
Law of conservation of mass (_______________):
1)Mass(matter) is NOT created or destroyed in ordinary chemical and physical ____________.
Ex. 2H2 +
20g +
O2 2H2O
X
Ex. 2Na + 2H20 2NaOH + H2
30g
35g +
X
 65g + 40g
2)Law of _________________Proportions
A chemical ________________ contains the ___________ proportions by mass no matter the
size or source or the sample. Always the same ____________.
In the year _____________
John Dalton __________________these laws
using experimental _____________ of other scientists.
Dalton proposed an atomic ______________ that included ________ _______________:
1. All _____________ is composed of tiny particles called
___________.
2. Atoms of the ____________ element are ______________;
atoms of different elements are _______________.
3. Atoms cannot be __________________, created, or destroyed
4. Atoms of different elements combine in simple ______________
______________ ratios to form a compound
5. In a chemical ________________, atoms are ______________,
separated, or rearranged, but not __________________.
Two of Dalton’s ___________ were proven ___________:
# 2: atoms of the ______ element _____ be different (____________)
# 3: atoms are __________________.
A “picture” of Dalton’s ____________
(called the___________________ Ball)
Today we define the atom as the _________________ particle of an
_________________ that retains the _________________ of that element.
The subatomic particles are:
proton - ___________________ charged; in the _______________
neutron - ________________; in the ________________
electron - ________________ charged;_________________the nucleus
JJ Thompson discoverer of the __________________in __________.
(______________________ ______________)
Studied the results of running _________________ currents
through small amounts of _________ in a sealed glass tube - cathode _______ tube (______).
He noticed a ____________ of particles he called a _________________ ray that:
1.cast a ______________ if an object was placed in their ___________
2. had enough ___________ to move a small paddle _____________
3. were deflected by a _________________ field the same way as a wire
carrying _______________ current (electric current was known to have
a ________________ charge)
4. were deflected ___________ from a ___________________ charged
object (like charges _____________).
From these experiments, Thomson concluded:
5. cathode rays are __________________.
6. cathode rays always have the ___________ charge to mass
__________.
Later these cathode rays were named __________________ (the ____________ subatomic
particle discovered)
A “picture” of Thomson’s model: (called the plum _______________ model)
Because these guys learned about electrons, two other assumptions could be made:
1. Since atoms are electrically neutral, they must contain a
_______________charge to balance the negative electrons.
2. Because electrons have such low mass, there must be
_____________ __________________ to make up for the mass.
Ernest Rutherford _____________, discovered the________________.
Bombarded gold foil with alpha particles (positive He)
He expected the alpha particles (Helium particles) to go ______________
the foil, but some of the alpha particles _________________ back.
Rutherford concluded that atoms contain a ____________, dense
____________________ -charged area and the ________________ move
around this _________________ like planets around the sun.
Neils Bohr________
Electrons circle the nucleus in allowed paths or ___________.
Electrons absorb _______________ to get to farther orbits and _________ ______ energy
when returning to original orbits.
Electron Cloud Model (Current Model)
Erwin Schrodinger ___________
Quantum mechanics electrons can on exist in specified energy states.
Electron cloud model
_____________: 3-d region around the nucleus where e- are likely to be found.
James Chadwick _________
Discovered neutrons - ___________ particles in
the nucleus that accounted for the additional mass of an atom.
(neutrons & protons make up the mass of an atom)