Happy Mole Day!
Mole day is celebrated every October 23rd
between 6:02 in the morning and 6:02 in the
evening.
Scientists celebrate mole day because the
mole is the SI base unit for the amount of a
substance.
The number of particles in 1 mole of any
substance is 6.022 X 1023, which is Avogadro’s
number.
We will learn more about the mole in section
3.4 as we begin counting atoms…
Just How Big is a Mole?
Avogadro's number of pennies placed side by
side would stretch for more than 1 million light
years!
This amount of pennies would also be good
enough to repay the debt of United States of
America 86 million times!
Mole Day Riddles…
What do you call a 10th grade chemistry student?
A sophmole
What does Avogadro put in his hot chocolate?
Marsh-mole-ows!
Why did Avogadro stop going to a chiropractor on
October 24th?
He was only tense to the 23rd.
Wednesday, Oct. 23rd: “A” Day
Thursday, Oct. 24th: “B” Day
Agenda
Happy Mole Day!
Homework Questions? (pg 78: #1-8)
Sec. 3.1 Quiz: “Substances are Made of Atoms”
Begin Sec. 3.2: “Structure of Atoms”
KWL Activity
J.J. Thomson, cathode rays, electrons, Ernest
Rutherford , gold foil experiment, nucleus, protons,
neutrons, Coulomb’s law
Homework: Concept Review and KWL
Ch. 2 Tests
“Matter and Energy”
Class
Average Score
(out of 60)
Average
Percentage
2A
48.52
80.87 %
4A
51.93
86.55 %
1B
52.00
86.67 %
3B
53.32
88.87 %
Sec. 3.1 Quiz
“Substances are Made of Atoms”
I thought the quiz for
this section was a little tricky,
so we’re going to go through
some of it together as a
review…
You’re welcome! 
Atomic Structure KWL Activity
KWL stands for:
“K”: What I KNOW or think I know
“W”: What I WANT to know
“L”: What I LEARNED
Take a few minutes to write down at least 5 each
in the “K” and “W” sections of the KWL graphic
organizer before we begin Section 3.2: “Structure
of Atoms
Keep this handy because you’ll complete the “L”
section as we work through the chapter…
Sec. 3.2: “Structure of Atoms”
Scientists discovered that atoms CAN be
broken down into smaller parts called
subatomic particles.
The 3 types of subatomic particles that are
most important in chemistry are:
Electrons
Protons
Neutrons
Electrons Were Discovered by Using
Cathode Rays
J.J. Thomson was studying electricity, not atomic
structure, when he discovered electrons.
He pumped the air out of a sealed glass tube
and attached electrodes to each end.
Anode: positive electrode
Cathode: negative electrode
A glowing beam came out of the cathode.
He called the beam a “cathode ray”.
The glass tube is known as a cathode ray tube
(CRT)
An Electron has a Negative Charge
Thomson reasoned that the ray was negatively
charged since it was coming from the cathode.
He placed a magnet by the tube and saw the
ray deflected.
He placed a small paddle wheel in the path of
the ray and saw the wheel turn, showing that
something with mass was hitting the wheel.
Thomson concluded that the ray was made of
negatively charged particles that have mass.
Thomson called these particles electrons.
J.J. Thomson Discovered Electrons
Electron: a subatomic particle that has a
negative charge.
There Must be Other Subatomic
Particles Too…
Scientists began to look for more subatomic
particles for 2 reasons:
1. Since electrons have a negative charge but
atoms have no charge, there must be other
subatomic particles that have a positive
charge to balance out the electron’s negative
charge.
2. The mass of an atom is much larger than the
mass of an electron, so there must be other
subatomic particles in the atom.
Thomson’s Plum Pudding Model
J.J. Thomson proposed that electrons were
embedded in a ball of positive charge.
Thomson called this model the “plum pudding
model”.
Ernest Rutherford’s Gold Foil
Experiment
Rutherford Discovered the Nucleus
Rutherford directed a beam of positively
charged alpha particles at a thin foil of gold.
Most of the particles passed straight through
the foil, but a few were deflected, some even
backwards.
Only a very concentrated positive charge in a
tiny space within the gold atom could possibly
repel the fast-moving alpha particles enough
to reverse their direction.
The mass of this tiny, positively charged region
must be larger than the mass of the alpha
particle or it would simply have been knocked
out of the way.
Rutherford Discovered the Nucleus
Rutherford hypothesized that atoms are
mostly empty space except for the dense
center, or nucleus.
Nucleus: an atom’s central region, which is
made up of protons and neutrons.
The nucleus has all of the positive
charge, nearly all of the mass, but
only a very small fraction of the
volume of the atom.
Protons are in the Nucleus
The positively charged particles in the nucleus
were called protons.
Proton: a subatomic particle that has a
positive charge and that is found in the
nucleus of an atom; the number of protons of
the nucleus is the atomic number, which
determines the identity of an element.
A proton’s mass is about 2,000 times that of
an electron!!
There Must be Something Else…
Because an atom’s mass is greater than the sum
of its protons and electrons, scientists began
looking for another subatomic particle…
Protons + Electrons = Mass of Atom
James Chadwick Discovered
Neutrons
Neutron: a subatomic particle that has no
charge and that is found in the nucleus of an
atom.
A neutron has about the same mass as a
proton.
Coulomb’s Law
Coulomb’s law: the closer two charges are,
the greater the force between them. (Think of
magnets)
Also, the larger the two charges are, the greater
the force between them.
Why is the Nucleus Stable?
If the nucleus is made up of positively charged
protons and neutrons with no charge, why
doesn’t the force of repulsion push the
protons apart and make the nucleus unstable?
THE STRONG FORCE!
The Strong Force
A fundamental force of nature, the strong
force, overcomes the repulsive forces between
positively charged protons in the nucleus.
All atoms that have more than 1 proton also
have neutrons to help stabilize the nucleus.
Homework
Not only have we covered a lot today, we didn’t
finish this section, so there’s NO HOMEWORK for
today!
However, please use this time
to work on the concept review
and/or your KWL
We’ll finish section 3.2 next time…