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Atoms
Miss Sauer’s 7th Grade Science
Bill Nye: Atoms
• https://www.youtube.com/watch?v=96JYhfd7-50
Atoms
• All matter is made up of atoms. Atoms are matter. Atoms are the building blocks of
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matter.
Atoms are mostly empty space.
All liquids, solids, gases, & plasmas are made up of these tiny particles.
Atoms are extremely small. Atoms are so small that in just one drop of water, there
are about six sextillion atoms (6,000,000,000,000,000,000,000).
Atoms are the smallest particle into which an element can be divided and still be the
same substance.
Many scientists and philosophers have investigated and worked with ideas.
Atoms
• Atoms are composed of electrons, protons, and neutrons.
• The nucleus of an atom is made up of protons and neutrons.
• Electrons are the least massive particle of the atom and travel around the
nucleus.
• Protons are positively charged.
• Neutrons have a neutral charge (no electric charge).
• Electrons are negatively charged.
Democritus
• Greek philosopher who named the atom in 440 BC.
• Said all atoms are small, hard particles made of a single material formed into
different shapes & sizes.
• He believed the atom was indivisible.
• In Greek, atomos means indivisible.
Democritus – Atom Drawing
Aristotle
• Lived from 384 to 322 BC.
• Believed you would never end up with an indivisible particle.
• (no such thing as a smallest particle)
Aristotle – Atom Drawing
John Dalton
• Late 1700’s
• All substances are made of atoms. Atoms are small particles that cannot be created,
divided, or destroyed.
• His atomic theory stated that all atoms of the same element are alike. All atoms of
different elements are different. (If it’s not on the periodic table, it’s not an element)
• Atoms join with other atoms to make a new substance (we call this molecules).
Atoms together are called molecules.
• He performed experiments, which Democritus did not do.
• We believe most of this today, except today we know about subatomic particles.
John Dalton – Atom Drawing
J.J. Thomson
• 1897
• Discovered there are small particles inside an atom using a Cathode Ray Tube; proved
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electrons exist.
He called the negatively charged particles electrons.
Created a model known as the Plum Pudding Model (his model of the atom resembled
plum pudding).
First subatomic particle discovered (the electron).
Discovered the electrons.
Negatives have to equal the positives.
Repeated the experiment to make sure it was right (same results each time).
J.J. Thomson – Atom Drawing
Cathode Ray Tube
• Cathode Ray Experiment
• https://www.youtube.com/watch?v=_nLESblUAHY
Plum Pudding Model
• Thomson's Plum Pudding Model of the Atom
• https://www.youtube.com/watch?v=JUJPyQtoB5E
Ernest Rutherford
• 1909 (Former student of Thomson).
• Through the Gold Foil Experiment he created a new atomic theory.
• He aimed positive particles at gold foil coated with zinc sulfide, a substance
that glowed when struck by particles.
• He discovered the dense and positively charged region known as the nucleus.
• Concluded that the atom is mostly empty space with a dense core (the
nucleus).
Ernest Rutherford – Atom Drawing
Gold Foil Experiment
• Gold Foil Experiment
• https://www.youtube.com/watch?v=zUtIrO3fUgg
Results of the Gold Foil Experiment
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The discovery of the nucleus
The nucleus is positively charged
Most of the mass is concentrated in the nucleus
The nucleus is tiny compared to the atom as a whole
The atom is mostly empty space
Niels Bohr
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1913
Stated the electrons travel around the nucleus in definite paths.
He thought of the electrons as rungs on a ladder.
That electrons stood only on the steps, not in between)
Niels Bohr – Atom Drawing
The Modern Theory:
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Electrons are likely to be found in regions in between.
These regions are called the electron cloud.
Electrons follow the paths described in Bohr’s Model.
Electrons are not in a fixed position; they are somewhere in the electron
cloud.
The Modern Theory – Atom Drawing
Timeline
440 BC
Democritus
names the
atom
384 to 322 BC
Aristotle does
not believe there
is a smallest
particle
Late 1700’s John
Dalton conducted
experiments and
stated all atoms of
the same element
are alike
1909
Ernest Rutherford
(Gold Foil
Experiment)
discovered the
dense and positively
charged region
known as the
nucleus
1897
J.J. Thomson (Plum
Pudding Model &
Cathode Ray Tube);
Discovered electrons
1913
Niels Bohr stated
the electrons
travel around the
nucleus in
definite paths
Present
Modern Theory:
electrons are not
in a fixed
position; they
are somewhere
in the electron
cloud
Parts of the Atom
Electron Orbits
• To determine the number of electrons that can be held in the first orbit
(closest to the nucleus):
Use this formula: 2n2 (where n is the level of the orbit)
Sub in 1 for n, because we want to know how many electrons can fit in the first
level of orbit.
2(1)2
First multiply the exponent, then multiply the parenthesis.
12 = 1 x 1=1, then 2(1) = 2
Electron Orbits
• To determine the number of electrons that can be held in the second orbit:
Use the same formula: 2n2 (where n is the level of the orbit)
Sub in 2 for n, because we want to know how many electrons can fit in the
second level of orbit.
2(2)2
First multiply the exponent, then multiply the parenthesis.
22 = 2 x 2 = 4, then 2(4) = 8
Electron Orbits
• To determine the number of electrons that can be held in the third orbit:
Use the same formula: 2n2 (where n is the level of the orbit)
Sub in 3 for n, because we want to know how many electrons can fit in the
third level of orbit.
2(3)2
First multiply the exponent, then multiply the parenthesis.
32 = 3 x 3 = 9, then 2(9) = 18
Electron Cloud
• The size of the electron cloud determines the size of the atom.
• The weighted average of the masses of all the naturally occurring isotopes
of an element is called atomic mass.
• Atomic Mass Unit (amu) is the SI unit used for the masses of atomic
particles.
Isotopes
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Have the same number of protons but different numbers of neutrons
Share most of the same chemical properties.
Share most of the same physical properties.
Are NOT stable when radioactive.
Forces on the Atom
• Gravity: depends on the mass of objects and the distance between them.
• Electromagnetic Force: holds the electrons around the nucleus.
• Strong Force: counteracts the electromagnetic force so protons stay together
in the nucleus.
• Weak Force: plays a key role in neutrons changing into protons and electrons
in unstable atoms.
Parts of the Atom
Parts of the Atom
• Most of the mass of an atom is found in the central part of the atom called the
nucleus.
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The nucleus of an atom is made up of protons and neutrons.
These particles (protons & neutrons) are packed very tightly together in the nucleus.
Electrons are found outside the nucleus.
They circle the nucleus very, very quickly. Electrons are very small and have almost
no mass.
• The number of electrons in an atom is ALWAYS EQUAL to the number of
protons in the nucleus of that atom.
Parts of the Atom
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Protons have positive (+) charges.
Electrons have negative (-) charges.
Neutrons have no charges. They are neutral.
Since atoms have the same number of protons and electrons, the number of
positive charges equals the number of negative charges. The opposite
charges cancel each other out. Therefore, the whole atom has no overall
charge.
• Protons determine the identity of the elements.
APE
APE
Atomic Number = # of Protons = # of Electrons
So, if the Atomic Number is 27, there are 27
Protons in the element, & there are 27 Electrons.
All 3 are equal!
Subatomic Particles
Sub-Atomic Particle
Mass in AMU’s
Charge
Location in Atom
Protons
1 AMU
+
Inside the nucleus
Neutrons
1 AMU
0
Inside the nucleus
Electrons
1/1,840 = 0 AMU
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In the electron cloud/outside the nucleus
Electrons are not included in the atomic mass because they are so small.
Ions
• If an element turns into an ion, the number of electrons WILL NOT
equal the number of protons. Positives will not equal the negatives.
Atomic Mass
Atomic Mass = Protons + Neutrons
(Remember: Most of the mass is
concentrated in the nucleus!)
Elements
• The first letter of an element is capitalized (upper case), the second letter is
lower case.
• Example: Fe
• Elements are arranged on the periodic table according to their number of
protons.
• Elements are different because of the different number of protons in
the nucleus.
Look at the Periodic Table
8
Atomic Number
O
Symbol
Oxygen
Element Name
15.999
Atomic Mass
Atomic Number & Atomic Mass
ATOMIC NUMBER equals the number of PROTONS or ELECTRONS.
ATOMIC MASS equals the number of PROTONS + NEUTRONS.
Atomic Number & Atomic Mass
ATOMIC NUMBER equals the number of PROTONS or ELECTRONS.
Example: Boron, Atomic Number: 5; # of Protons: 5; # of Electrons: 5
ATOMIC MASS equals the number of PROTONS + NEUTRONS.
Example: Boron, Atomic Mass: 10.81; # of Protons: 5 + # of Neutrons: 5.81
5 + 5.81 = 10.81
Closure Questions
• Give elements and ask: atomic number, atomic mass, # of protons, # of
electrons, & # of neutrons.
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Parts of the atom (location, charge, mass).
How to draw an atom of an element.
How to write symbol for elements.
Isotopes exist because?
Figure out the # of protons given the atomic mass or atomic number.