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Introductory Chemistry
Subshell order of filling, numbers of subshells, orbital population, electron spin, magnetism
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Dr. Walt
Volland revised March 31, 2005
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Orbitals, s, p, d, f and
average distance from the nucleus
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Orbitals are the
regions of space occupied by electrons in atoms. The shapes and volumes
of space are different for each type of orbital. The electrons are confined
to specific shaped spaces around the nucleus. The electrons are not
on the surface of these shapes. The electrons are moving inside the
volume marked out by the shape.
- The shape for
all "s" orbitals is spherical with the center of the sphere at the
nucleus. The size of the sphere increases for increasing quantum numbers.
The 1s has a smaller
diameter than the 2s and so forth.
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1s <
2s < 3s < 4s < 5s < 6s < 7s
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The
p orbitals have a double lobe shape with the point of contact of
the lobes at the center of the nucleus. The three different p orbitals
are each aligned along one of the three coordinate axes x, y, or
z.
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principle quantum number "n" is very useful. It tells the
relative energy for an electron in an atom and it also indicates the
average distance between the nucleus and an electron. The higher the
value for "n" the greater the distance between the nucleus
and the electron. An electron in the first level, n = 1, is closer
to the nucleus on average than an electron in the n = 4 shell.
- Exercise:
- What do the subscripts x,y an z indicate about the "p" orbitals in a shell? Click here for answer
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Number of orbitals
in a shell
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The number of each
type of orbital has a mathematical origin. You need to know only the
results of the math.
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orbital
type
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s
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p
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d
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f
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maximum
number of orbitals in a shell
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1
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3
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5
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7
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number of
electrons that can fit into orbital type
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2
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6
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10
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14
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Notice that the
number of orbitals increases by "2" in going from one type to another.
The capacity for electrons increases by "4" at the same time.
Exercise:
How many "g" orbitals would you predict? Answer:
There should be 9 and they could hold 18 electrons.
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Number of electrons
in an orbital and electron spin
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Every orbital can
only hold two electrons. This is linked to the magnetic character of
electrons. The electrons act as though they are spinning charged particles.
There are two spin directions that match the two magnetic fields created
by electrons. There is a spin up field and a spin down field. Commonly
the two magnetic fields and spin types are indicated by arrows. An up
arrow for spin up and a down arrow for spin down. The pairing of the
magnetic fields of two electrons cancels out the fields and sets the
limit on the population of an orbital at two.
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Maximum number
of electrons in any orbital = 2
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Atoms with all the
electron spins paired have no magnetic character. An
atom with unpaired electrons shows magnetic properties.
This is the origin of the magnetic behavior of iron and nickel for example.
This magnetic property gives us a way to know how the electrons are arranged
in atoms. Particles with unpaired electrons are called as "free radicals".
Free radicals have been linked to the aging process, mutations in DNA,
and cancer.
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