Transcript Slide 1

ATOMIC orbitals!
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.
http://atomictimeline.net//index.php
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.
http://atomictimeline.net//index.php
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.
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.
http://hti.math.uh.edu/curriculum/units/1999/02/07/99.02.07.ph
p
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.htm
l
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.
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
Sodium
23
Na
11
(2,8,1)
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s1
angular momentum number
principal quantum number
Na
type of orbital
parts
s
p
d
f
1
3
5
7
max number of e-
2
6
10
14
1s
2s
3s
4s
5s
6s
7s
2p
3p 3d
4p 4d 4f
5p 5d
6p
list a sequence here
Scribble by Mr G
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.
http://dbhs.wvusd.k12.ca.us/webdocs/Electrons/QuantumNumbers.htm
l
= nucleus