Download 9/28-29 Atomic Structure Rev, Mole, Avg. Atomic Mass

Average Atomic Mass
Moles
Start Atomic History
Chemistry 9/28/15
Drill
Pick up the half-sheet for the drill.
Put your HW out on the desk to be checked.
HW:
Average Atomic Mass Calculation
Formula Mass and Mole Conversion Practice Problems
Objectives
IWBAT
Calculate the formula mass or molar mass for any
compound.
Convert between moles, grams, and particles for any
element or compound
Trace the development of Atomic Theory from
Democritus to the present day.
HW Review
Atomic Structure WS
3-3 Practice Problems WS
State the number of moles
in 58.4 grams of Carbon.
12.01 g C = 1 mol C
58.4 g C = ? mol C
58.4 g C x 1 mol C = 4.86 mol C
12.01 g C
The Mole
If you have 10.0 g of water, how many
molecules in that amount?
10.0 g H2O
x
1 mol
x
18.02 g H2O
=
6.022 x 1023 molecules
1 mol
3.34 x 1023 molecules of H2O
The Mole
If you have 25.0 g of copper (II) sulfate, CuSO4,
how many formula units are in that mass?
25.0 g CuSO4
x
1 mol
159.61 g
CuSO4
=
x
6.022 x 1023 formula units
1 mol
9.43 x 1022 formula units of CuSO4
Mole Practice
Mass and Mole,
Mole and Avogadro’s Number
Complete the practice at your desk. Ask Ms. Bloedorn for
help if you have questions
Average Atomic Mass
Go back to the Atomic Structure notes from last
week. Let’s finish the bottom!
4A
Quiz Review
Ms. Bloedorn will hand back your Unit 2 Quizzes—
take a look, ask questions, return to her.
Let’s take a turn…
To HISTORY!
Dalton’s Atomic Model - 1805
Atoms are indivisible units of matter that are
unique for each element, and combine to
make various compounds.
A lump of gold is made of tiny gold pieces (atoms).
Carbon dioxide is made of tiny carbon and oxygen
pieces (atoms) combined together.
These atoms cannot be broken down further.
Was there any science involved in this model?
YES! John Dalton did many scientific
experiments, especially with gases, to formulate
his ideas.
Dalton’s Atomic Theory of Matter
Four Postulates:
All matter is composed of extremely small
particles called atoms.
Atoms of the same element are identical,
and atoms of different elements are
different from those of any other element.
Atoms are neither created nor destroyed in
any chemical reaction.
Atoms combine in definite proportions
(the same proportion) to form compounds.
Ex. CO vs. CO2
J. J. Thomson – 1898
Thomson took advantage of new technology
– the cathode ray tube.
Cathode “rays”/particles – negatively
charged, very light (but they do have mass—
Milliken’s Oil Drop Experiment), came from
atoms.
Thomson’s Discovery
Thomson knew
atoms were usually
neutrally charged.
So, he realized that
if he could remove
a negative particle,
there must be a
positively charged
part also.
Thomson’s Conclusions
Thomson’s model of the atom is
heterogeneous and solid, but NOT indivisible.
Electrons can be removed, so it can be divided.
The Plum Pudding Model – Solid sphere of
positive charge with electrons spread
through it like raisins or plums in a plum
pudding.
Robert Millikan – 1910
Millikan, using a set-up seen in your diagrams,
calculated the charge of the electron using oil drops.
This also PROVED that there were such things as
subatomic particles—some people still had doubts.
It also introduced the idea of a quantized charge.
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 [email protected]
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.
Exit Ticket
An atom has 12 protons, 11 neutrons, and 10 electrons.
Write the full symbol and full name for this atom.
Calculate the average atomic mass of this element,
using the data. Show your work:
Mass number (amu)
Natural abundance (%)
10
19.9
11
80.1
How many moles are in 6.022 x 1025
molecules?