Download Atomic Theory, cont*d

Atomic Theory, cont’d
Chemistry 10/7/14
Drill
Write the complete symbol for these atoms. Also,
determine if they are ions, isotopes, or both!
40 protons, 51 neutrons, 38 electrons
5 protons, 5 neutrons, 5 electrons
9 protons, 11 neutrons, 10 electrons
HW: pg. 4 Atomic Structure
Objectives
IWBAT
Find or calculate atomic mass, atomic number, number
of protons, neutrons, and electrons, charge, etc. for
any atom
Trace the development of Atomic Theory from
Democritus to the present day.
NOTE: Quiz#3 on Atomic Structure on Friday, 10/10
Rutherford’s Gold-Foil
Experiment - 1911
Rutherford and
Radioactivity
Ernest Rutherford used
alpha particles to
investigate the gold atom
in 1908.
We will learn more about
alpha particles next week.
He conducted a famous
experiment that proved
that atoms are not solid
spheres as proposed by
Dalton, or “plumpuddings,” as Thompson
said.
The Alpha Particles
Experiment
In his experiment Rutherford used a very thin
sheet of gold as a target, and he shot a beam of
alpha particles at the gold.
alpha particles (-particles) are helium nuclei
without electrons, and are a form of
radioactivity
Nearly all of the alpha particles passed through
the thin sheet of gold.
Rutherford also noticed that a few particles
were deflected from their straight- line path,
some by 90 degrees or more.
Conclusion
The beams were bouncing off the positively charged
core of the atoms.
Rutherford originally called this a proton, because it
was positively charged.
Later, it was renamed the nucleus. The nucleus of the
atom has almost all the mass of the atom.
Therefore, most of an atom is empty space.
Bohr Model
(the one you all know)
Niels Bohr - 1913
Bohr said electrons were in set orbits, like rungs of a
ladder.
You can only be on one orbit (rung) or the next, not in
the middle -- they are quantized
Electrons can only move from one to the other by
emitting or absorbing a particular wavelength of
light (a photon with a certain energy), similar to the
metal in the photoelectric effect.
Atomic Excitation
Picture by
Schrödinger's/ Modern
model of the atom
Particle-Wave Nature of
Matter
Light has a particle nature
(Einstein-1905):
photon – quantum of energy that
behaves in some ways like a particle
Matter has a wave nature (De
Broglie-1924):
Electrons scatter like X-rays
Electron microscopes use this
property to see very small things.
Heisenberg’s Uncertainty Principle
The position and
speed of a moving
object cannot BOTH
be known exactly at
the same time.
Heisenberg, Cont.
Why?
The act of observing changes an object.
To see things, we must bounce light off of
them.
To observe an electron, we have to bounce
light off of it.
The light would move the electron so much
that we would not be able to tell where it was,
or how fast it was going.
Think of hot tea and a cold thermometer.
A new idea!
Orbitals:
A region around the nucleus of the atom
where an electron of a given energy is likely to
be found.
We don’t know exactly where electrons really
are, just where they are likely to be.
Also called an electron cloud or probability
region.
So, what’s an orbital??
Orbit  Orbital
ex. Electron is
like a bee around
a beehive.
Closure
What is another metaphor you could use for
the Plum Pudding model?
How many electrons would Fe3+ have?