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Chapter 1
Activity 4: Are Atoms Divisible?
(1st Verse)
They’re tiny and they’re teeny,
Much smaller than a beany,
They never can be seeny,
The Atoms Family.
(Chorus)
(2nd Verse)
Together they make gases,
And liquids like molasses,
And all the solid masses,
The Atoms Family
(Chorus)
(3rd Verse)
(Chorus)
(Chorus)
They are so small.
(snap, snap)
They’re round like a ball.
(snap, snap)
They make up the air.
They’re everywhere.
Can’t see them at all.
(snap, snap)
Neutrons can be found,
Where protons hang around;
Electrons, they surround
The Atoms Family.
(Chorus)
(4th verse)
The periodic table,
It isn’t just a fable;
You’ll read it when your able;
The Atoms Family
(Chorus)
Ancient Greece
1. Greek philosopher
Democritus
2. He thought atoms were uncuttable
3. Therefore: Atoms are indivisible
particles
Atomos—Greek meaning ‘indivisible
470-380 B.C.
John Dalton—late 18th century
1. What are atoms?
Dalton’s Atomic Model:
Hard, indivisible sphere
1766-1834
2. Do Carbon atoms differ from
Oxygen atoms?
Yes
HAS THIS EVER
HAPPENED TO YOU?
Are there things inside the atom?
YES!
Subatomic particles- particles
that are smaller than the atom
+
e p n0
Discovery of electron (e-)
Discovered the electron in 1897.
J.J. Thomson
1856-1940
• Identified a glowing beam of
particles that traveled through a
chamber of gas when exposed to
an electrical current.
Cathode ray tube
-This beam (cathode ray) was attracted to
positive charges and repelled by negative
charges.
-Thomson concluded the beam must be
composed of negatively charged
particles. These came to be known as
electrons.
Thomson’s Atomic Model
“Plum Pudding” Model
POSITIVE
CHARGE
Negative electron plums are
floating around in a sphere of
positive pudding.
ELECTRONS
EMBEDDED
WITHIN
Discovery of the Nucleus
1871-1937
Ernest Rutherford
Rutherford’s Au foil Experiment
-Discovered the Nucleus
(through the Gold Foil Experiment)
“+” charge
-Discovered that the atom is
mostly empty space
-Alpha particle: a positively
charged particle, consisting of
two protons and two neutrons
(helium nucleus).
Rutherford’s experiment
Rutherford’s Nuclear Atom
Negative electrons
surround nucleus
amidst lots of empty
space.
Positive
Nucleus
Discovery of the proton
Eugen Goldstein
In 1886, Goldstein
observed rays in a
cathode ray tube
that traveled
oppositely than the
electrons previously
discovered.
James Chadwick
1. Discovered the neutron in 1932
2. This subatomic particle is heavy enough to
split a nucleus
3. Led the way to the creation of the atomic
bomb
Ch 1:
Activity 4
Protons
Located in nucleus
Determine which element (DNA)
# of protons = atomic number

equal to # of electrons in a neutral atom
LETS HAVE SOME PRACTICE
Element
Symbol
Element
Name
Mass Number
(Protons+Neutrons)
Atomic
Number
(Protons)
Atomic
Number
(Protons)
6
C
Carbon
12
12
6
Mass Number
(Proton+Neutrons)
C
Mass Number
Almost all the mass of an atom comes
from protons & neutrons
# Protons + # Neutrons = mass
number
REVIEW TIME
Atomic # = # of protons (P)
# protons = # electrons in an atom
Mass # = number of protons and neutrons
(P + N)
So,to get the # of neutrons we must Subtract
Atomic # from the Mass # = # Neutrons
12
6
C
6 neutrons
Practice
Determine the # of protons,neutrons, & electrons
Protons
Neutrons
Electrons
He
2
2
2
B
5
6
5
Mg
12
12
12
Zn
30
35
30
Subatomic Particles
Electron: enegative charge
-31 kg
 9.11 x 10

Proton: p+
positive charge
-27 kg
 1.67 x 10

Neutron: n0
no charge
-27 kg
 1.67 x 10

What did Battleship teach us?
Battleship simulated Rutherford’s Gold Foil Experiment.
Rutherford
Alpha Particles
Battleship
Your missiles
Nucleus
Pattern Drawn
Atom is mostly empty
space
All of the empty boxes
Atoms vs Ions
ATOMS
IONS
Protons = Electrons
Protons ≠ Electrons
Cations= More Protons
Positive Charge
Anions= More Electrons
Negative Charge
IONS
cation (+)
anion (-)
Li+1
Cl-1
3 Protons
2 Electrons
17 Protons
18 Electrons
Can’t Change the
Number of Protons
Ions
An ion is an atom with a
positive (+) or negative (-)
charge
Atoms that gain electrons
have - charges
Atoms that lose electrons
have + charges
Isotopes
Atoms of an element can
have different numbers of
neutrons – these are
isotopes
The number of protons is
always the same, but
since more neutrons add
more mass, the mass
number can be different
Isotopes
Protons = Protons
BUT……#Neutrons are Different
So
Mass # is Different
Atom
Protons
Neutrons
Electrons
Mass #
Carbon-12
6
6
6
12
Carbon-13
6
7
6
13
Carbon-14
6
8
6
14
Isotopes
How Big Is An Atom?
The Scale of the Universe
http://htwins.net/scale2/
Practice
•
The atomic number of an atom is always
equal to the total number of:
a. Neutrons in the nucleus
b. Protons in the nucleus
c. Neutrons plus protons in the nucleus
d. Protons plus electrons in the atom
Practice
•
If the number of electrons and protons are
not equal:
a. an atom exists
b. an isotope exists
c. an ion exists
d. None of the above
Practice
•
An atom that has lost electrons has what
type of charge?
POSITIVE
•
Once it has lost electrons it is no longer
an atom. What is it called?
CATION
Practice
•
An atom of 42Ca contains:
a. 20 protons and 22 neutrons
b. 20 protons and 42 neutrons
c. 20 electrons and 42 neutrons
d. 20 electrons and 22 protons
Practice
•
Atoms that have the same atomic number
but different mass numbers are called?
isotopes
Practice
•
Look at the picture below and then fill in the
chart:
Atom
Protons
Neutrons
Electrons
Mass #
Lithium-6
3
3
3
6
Lithium-7
3
4
3
7
Lithium-8
3
5
3
8
Practice
•
The nucleus of an Fe-56 atom contains:
a. 26 protons, 30 neutrons and 26 electrons
b. 26 protons, 26 neutrons and 30 electrons
c. 26 protons and 56 neutrons
d. 26 protons and 30 neutrons
Practice
•
What did Rutherford’s Gold Foil experiment
discover?
a. electron
b. neutron
c. nucleus
d. proton
Practice
•
A 52Cr3+ ion contains:
a. 24 protons, 52 neutrons, 21 electrons
b. 24 protons, 28 neutrons, 24 electrons
c. 24 protons, 28 neutrons, 27 electrons
d. 24 protons, 28 neutrons, 21 electrons
Practice
•
What is the total number of electrons in
an atom with an atomic number of 30
and a mass number of 65?
a. 30
b. 65
c. 35
d. 95
Practice
•
Who discovered the electron and how?
a. Democritus, atomic theories
b. Dalton, cathode ray tube
c. Rutherford, gold foil experiment
d. Thomson, cathode ray tube