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Previously we learned that the average human
body has 10,000,000,000,000 (10 Trillion)
cells
Q: How many atoms are in one cell?
A: 200,000,000,000,000
100 x more than there are stars in the milky
way
2,000,000,000,000,000,000,000,000
200 septillion atoms in the body
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Crash Course History of Atomic Structure
The term matter describes all of
the physical substances around
us: your table, your body, a
pencil, water, and so forth
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Anything that has
mass and takes up
space (has
volume)
Made up of
different kinds of
atoms
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Includes all things
that can be seen,
tasted, smelled, or
touched
Does not include
heat, sound, or
light
Models are often used for
things that are too small or
too large to be observed or
that are too difficult to be
understood easily
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In the case of atoms, scientists use large
models to explain something that is very
small
Models of the atom were used to explain data
or facts that were gathered experimentally.
So, these models are also theories
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Universe was
made of empty
space and tiny bits
of stuff
Called these tiny
bits of stuff
atomos
Atomos could not
be divided
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All elements are composed of indivisible
particles (atoms).
Atoms of the same element are the same
Atoms of different elements are different.
Compounds consisted of atoms of different
elements combined together
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Mostly empty
space
Small, positive
nucleus
Contained protons
Negative electrons
scattered around
the outside
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Used an electric current to
learn more about atoms
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Noticed “electrons” were
attracted to a positive end
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Sometimes called the
wave model
Spherical cloud of
varying density
Varying density shows
where an electron is
more or less likely to
be
 Nucleus
◦ Protons
◦ Neutrons
 Electrons
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Electrons
Tiny, very light particles
Have a negative electrical charge (-)
Move around the outside of the nucleus
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Protons
Much larger and heavier than electrons
Protons have a positive charge (+)
Located in the nucleus of the atom
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Neutrons
Large and heavy like protons
Neutrons have no electrical charge
Located in the nucleus of the atom
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Atomic Number = number of protons
In a neutral atom, the # of protons = the # of
electrons
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Atomic Mass Number - equal to the number
of protons plus neutrons.
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Atomic Number:
number of protons
in an element
◦ Zr=40 protons…and
_______electrons
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Mass Number:
Protons + neutrons
◦ H= 1 mass #
◦ He=4 mass #