ATOMIC orbitals!

1
ATOMIC orbitals!
2
When the a planet moves around the sun, you can
plot a definite path for it which is called an
orbit. A simple view of the atom looks similar
and you may have pictured the electrons as
orbiting around the nucleus. The truth is
different, and electrons in fact inhabit regions
of space known as orbitals. Orbits and orbitals
sound similar, but they have quite different
meanings. It is essential that you understand the
difference between them.
3
To plot a path for something you need to know
exactly where the object is and be able to work
out exactly where it's going to be an instant
later. You can't do this for electrons. The
Heisenberg Uncertainty Principle says - loosely -
that you can't know with certainty both where an
electron is and where it's going next. (What it
actually says is that it is impossible to define
with absolute precision, at the same time, both
the position and the momentum of an
electron.) That makes it impossible to plot an
orbit for an electron around a nucleus. Is this a
big problem? No. If something is impossible, you
have to accept it and find a way around it.
4
Hydrogen's electron - the 1s orbital
Suppose you had a single hydrogen atom and at a
particular instant plotted the position of the
one electron. Soon afterwards, you do the same
thing, and find that it is in a new position. You
have no idea how it got from the first place to
the second. You keep on doing this over and over
again, and gradually build up a sort of 3D map of
the places that the electron is likely to be
found. In the hydrogen case, the electron can be
found anywhere within a spherical space
surrounding the nucleus. The diagram shows a
cross-section through this spherical space.
5
95 of the time (or any other percentage you
choose), the electron will be found within a
fairly easily defined region of space quite close
to the nucleus. Such a region of space is called
an orbital. You can think of an orbital as being
the region of space in which the electron lives.
What is the electron doing in the orbital? We
don't know, we can't know, and so we just ignore
the problem! All you can say is that if an
electron is in a particular orbital it will have
a particular definable energy.
6
(No Transcript)
7
The three coordinates that come from
Schroedinger's wave equations are the principal
(n), angular (l), and magnetic (m) quantum
numbers. These quantum numbers describe the size,
shape, and orientation in space of the orbitals
on an atom.
8
The principal quantum number (n) describes the
size of the orbital. Orbitals for which n 2 are
larger than those for which n 1, for example.
Because they have opposite electrical charges,
electrons are attracted to the nucleus of the
atom. Energy must therefore be absorbed to excite
an electron from an orbital in which the electron
is close to the nucleus (n 1) into an orbital
in which it is further from the nucleus (n 2).
The principal quantum number therefore indirectly
describes the energy of an orbital.
The angular quantum number (Azimuthal Quantum
Number) (l) describes the shape of the orbital.
Orbitals have shapes that are best described as
spherical (l 0), polar (l 1), or cloverleaf
(l 2). They can even take on more complex
shapes as the value of the angular quantum number
becomes larger
There is only one way in which a sphere (l 0)
can be oriented in space. Orbitals that have
polar (l 1) or cloverleaf (l 2) shapes,
however, can point in different directions. We
therefore need a third quantum number, known as
the magnetic quantum number (m), to describe the
orientation in space of a particular orbital. (It
is called the magnetic quantum number because the
effect of different orientations of orbitals was
first observed in the presence of a magnetic field
9
Sodium
23
1s2 2s2 2p6 3s1
(2,8,1)
Na
11
1s2 2s2 2p6 3s1
angular momentum number
principal quantum number
10
max number of e-
type of orbital
parts
s p d f
1 3 5 7
2 6 10 14
11
1s 2s 3s 4s 5s 6s 7s
2p 3p 4p 5p 6p
3d 4d 5d
4f
list a sequence here
12
Scribble by Mr G
13

• Rules Governing the Allowed Combinations of
  Quantum Numbers
• The three quantum numbers (n, l, and m) that
  describe an orbital are integers 0, 1, 2, 3, and
  so on.
• The principal quantum number (n) cannot be zero.
  The allowed values of n are therefore 1, 2, 3, 4,
  and so on.
• The angular quantum number (l) can be any integer
  between 0 and n - 1. If n 3, for example, l can
  be either 0, 1, or 2.
• The magnetic quantum number (m) can be any
  integer between -l and l. If l 2, m can be
  either -2, -1, 0, 1, or 2.

14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
nucleus
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)