Monte Meyerink
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Describe the evidence for the existence of electrons,
protons, neutrons, and describe the properties of these
subatomic particles.
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Discuss atoms of different elements in terms of their
numbers of electrons, protons, and neutrons, and
define the terms atomic number and mass number.
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Experiments by scientists in the mid 19th century led
to a change in John Dalton’s atomic theory, which
stated that atoms were indivisible and indestructible.
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They discovered that atoms could be broken down
into pieces called subatomic particles.
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The three most important subatomic particles are the
electron, proton, and neutron.
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Electrons were discovered by J.J Thomson’s use of
cathode (electricity) rays.
◦ Rays had a negative charge since they originated from the
negatively charged cathode
◦ Rays consisted of tiny particles that were hitting the paddles
of the wheel.
◦ A cathode ray consisted of particles that have a very small
mass and charge of -1. We call these particles electrons (e-).
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Electrons exist on the edge of atoms in different shell
levels.
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Scientists began searching for the positively charged
area of an atom.
Ernest Rutherford used the gold foil experiment to
determine that there was a space in the atom that was
very dense, concentrated, and positively charged.
This region of the atom is called the nucleus.
◦ Contains nearly all of an atom’s mass, but a small fraction of
an atom’s volume.
◦ Located at the center of the atom.
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A proton (p+ or p) is a
positively charged particle
(charge of +1).
The charge of a proton was
calculated to be equal in
magnitude but opposite in
sign to the charge of an
electron.
The proton’s mass is 2000
times the mass of an
electron.
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Since protons and electrons
together did not account for
the entire mass of the atom,
scientist searched for another
subatomic particle.
This particle had to be neutral
to keep the atom stable.
James Chadwick projected
alpha particles at elements to
discover neutrons (n).
Neutrons have a charge of 0
and almost have the exact
same mass as protons.

Where are the protons, neutrons, and electrons
located in an atom?
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What are the charges of each subatomic particle?
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What are the relative masses of each particle in
regards to the total mass of the atom?
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Atomic Number: the number of protons that an atom
has.
◦ Hydrogen has an atomic number of one since it only has one
proton.
Carbon
Mercury
Plutonium
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Mass Number: the total number of particles in the
nucleus (protons + neutrons).
◦ Helium has a mass number of 2, one proton and one
neutron.
Lead
Gold
Bromine

Describe the evidence for the existence of electrons,
protons, neutrons, and describe the properties of these
subatomic particles.

Discuss atoms of different elements in terms of their
numbers of electrons, protons, and neutrons, and
define the terms atomic number and mass number.