Transcript File - C OF SCIENCE

Honors Chemistry
Section 5.2
The Quantum Theory and the
Atom
WHERE is the electron?
• We now know the electrons are
arranged in “shells” or “energy
levels” around the nucleus.
• …so how are they arranged in an atom?
• Neils Bohr suggested the electrons
were in “orbit”, like planets…
• Bohr thought that
when electrons
absorbed energy they
moved to one of his
higher “orbits”.
• Then, when they fell
back to a lower “orbit”,
these excited electrons
gave off that energy as
light waves.
• …but if electrons
“orbit” the nucleus
they would lose
energy constantly,
and fall into the
nucleus – but they
don’t!…
• So, exactly where
are the electrons in
an atom?
WHERE is the electron?
• Heisenberg reached the conclusion
that it is impossible to observe any
object without disturbing it —at
least a little.
• The smaller the object, the greater
the disturbance.
So What?
• Observing an electron produces an
unavoidable uncertainty about its
location or motion!!
• The Heisenberg uncertainty
principle states we cannot know the
motion and position of a particle at
the same time.
• We can know one, but not both!
The Electron Cloud Model
• Every time we detect the electron, we
change its speed and direction!
• We can’t tell where the electron IS…
(only where it WAS)…
• (think of a lightning bug blinking
around a bush…)
• We can only predict a zone where the
electron is most likely to be, the next
time we look. (it’s all a matter of
probability!)
The “Electron Cloud”
The “electron cloud” is a 3-D map of
dots showing where the electron
has been …
(There is NO
“cloud of
electrons”, just
a cloud of DOTS
showing where
the electron is
most likely to
be!
nucleus
Note that there is
no electron “path”!
The “Electron Cloud”
• This three-dimensional region around
the nucleus shows the electron’s
probable location. This is called an
atomic orbital. (NOT “orbit”!)
The dots are
most dense
where the
electron is found
most often.
nucleus
• The “boundary”
of an orbital
defines the
volume that
contains the
electrons 90% of
the time.
10%
90%
• (There is no
actual “boundary”,
because there is
actually a tiny probability the electron may be
anywhere!)
• The principal quantum number, “n” (n = 1 to 7),
tells what shell contains the orbital!
• These numbers for “n” (1 – 7) describe the size
(and energy) of the electron’s orbital.
• As “n” increases from 1 to 7, the
orbital is in a larger shell. The
electron spends more time farther from
the nucleus and has a higher energy.
An orbital with a higher “n” (principal energy
level) is in a shell that is (on average) farther
out from the nucleus, and has more energy!
th
rd energy
nd
4
energy level
level n=1
n=4
5
n=5
3
n=3
2
1st
n=2
O.K., so far…
• Electrons are located around the nucleus
in shells, or “energy levels” according to
their energy.
• These “shells” are called “principal
energy levels” (n), and are numbered
1-7. (n = 1 is the first shell, etc)
• The electrons actually exist in “orbitals”
(a 3-dimensional space) within each shell.
• A shell with a higher “principal quantum
number” (n) is (on average) farther out
from the nucleus.
• “Outside” shells (higher “n”) have
greater energy than “inside” shells.
How An Electron’s Energy Can
Change
1. When electrons absorb energy, they can move
farther away from the nucleus, into a higher
energy level, or shell. (to a higher “n”)
2. They can also move into another orbital that
has a more complex shape.
•Orbitals with complex shapes have higher
energy. (A simple shape requires less energy).
•Orbitals come in many shapes…
•The shape of the orbital depends upon
what kind of “subshell” the electrons are in!
SUBSHELL?!
YES! SUBSHELL! (or “sublevel”)
•Electrons exist in “orbitals”.
•Orbitals are found in subshells, which
determine the orbital’s shape.
•Subshells combine to make up shells,
(or principal energy levels).
•Shells combine to make the atom’s
“electron cloud”.
Subshells
•Each subshell type has its own energy, because
each type has its own shape…
•…and there are four kinds of subshells:
•In order of increasing energy, they are called:
“s”
“p”
“d” and “f” subshells
How Many Subshells are in each Shell?
•Energy level 1 (1st shell; n=1) has 1 subshell: s
•Energy level 2 (2nd shell; n=2) has 2 subshells: s & p
•Energy level 3 (3rd shell; n=3) has 3 subshells:
s, p, and d
…and…
•Energy level 4 (4th shell; n=4) has 4 subshells:
s, p, d, and f
Larger shells have more volume (more space)
to contain more subshells – more orbitals and
more electrons.
Orbitals are in Subshells
•Each type of subshell holds a different number of
orbitals, but each orbital can only hold 2 electrons.
• “s” subshells have only 1 orbital (max = 2 e-)
•“p” subshells contain 3 orbitals (max = 6 e-)
•“d” subshells contain 5 orbitals (max = 10 e-)
•And “f” subshells contain 7 orbitals! (max = 14 e-)
•All orbitals hold a MAXIMUM of 2 electrons!
Shell (E level)
subshells orbitals electron capac.
1st Shell (n=1) One “1s” One “1s”
2 electrons
2nd Shell (n=2) One “2s” One “2s”
2 electrons
One “2p” Three “2p”
3rd Shell (n=3) One “3s” One “3s”
6 electrons
2 electrons
One “3p” Three “3p”
6 electrons
One “3d” Five “3d”
10 electrons
4th Shell (n=4) One “4s” One “4s”
One “4p” Three “4p”
One “4d” Five “4d”
One “4f” Seven “4f”
2 electrons
6 electrons
10 electrons
14 electrons
Shells, Subshells, and Orbitals
For example, the third shell (n=3) has 3 subshells,
each with its own orbitals:
All in the 3rd shell! (9 total orbitals)
3d subshell contains five 3d orbitals
3p subshell contains three 3p orbitals
3s subshell contains one 3s orbital
So the 3rd shell (E level) can hold as many as 18
electrons (2 electrons per orbital)
The “s” orbital
Every shell has an “s”
subshell – a sphere.
Every “s” subshell has
only ONE orbital!
The 1s orbital
For every atom there is a single “1s” orbital.
The "1" in 1s means the orbital is in the 1st
energy level. The "s" indicates the shape of the
orbital. (All s orbitals are spheres surrounding
the nucleus).
The “p” orbitals
All shells above #1
contains a “p” subshell.
(The first shell with a “p”
subshell is the 2nd shell).
Each “p” subshell has three “p” orbitals (x, y, & z)
(These 3 orbitals are called “2px”, “2py”, & “2pz”)
Each “p” orbital can hold
up to 2 electrons.
“2” = 2nd shell!
Therefore, a “p” subshell can contain
up to: 6 electrons!
O.K. - So Far…
This is a 1s orbital!
(capacity = 2 e-)
This is a 2s orbital! (2 e-)
It’s bigger! (farther out)
This is a 2p orbital! (2 e-)
More complex shape, so
more energy!
This is the 2p subshell!
There are three p orbitals
for a total of 6 e-.
The Electron Cloud…Through Two Energy Levels!
The nucleus
1s orbital
2s orbital
2px orbital
2py orbital
2pz orbital
Total =
(10 electrons)
Electrons per shell…
Since the first shell has a single “s” subshell (1s)
with…
…ONE “s” orbital (called the 1s orbital),
the first shell can hold:
Just 2 electrons!
Since the second shell has an “s” AND a “p” subshell
(2s, 2p):
…it contains one “2s” orbital and three “2p” orbitals.
This means the 2nd shell has four orbitals and can
hold:
8 electrons!
The “d” orbitals
Every shell above #2
contains a “d” subshell.
Each “d” subshell has
five “d” orbitals!
Note how complex
the d orbitals are! (higher energy than p orbitals)
The 3rd shell is the first shell with a “d” subshell!
Each “d” orbital can hold up to 2 electrons.
Therefore, a “d” subshell can contain up to:
10 electrons!
The “f ” orbitals
Every shell above #3
contains a “f” subshell.
Each “f” subshell has
seven “f” orbitals!
The f orbitals are even
more complex (higher energy) than d orbitals!
The 4th shell is the first shell with a “f” subshell!
Each “f” orbital can hold up to 2 electrons.
Therefore, a “f” subshell can contain up to:
14 electrons!
The Quantum Theory (simplified)
Each electron has 4 quantum numbers to describe it…
1. The “principal quantum number” (n) = the shell number
2. The “angular momentum quantum #” (l )= the subshell type
3. The “magnetic quantum number” (ml) = which orbital
4. The “spin quantum number” (ms) = the spin (  or  ) of the
electron
EVERY ELECTRON IN AN ATOM IS UNIQUE, WITH ITS
OWN SET OF FOUR QUANTUM NUMBERS!