Chem 105 Wednesday 4 Nov 2009chem.uaf.edu/keller/Courses/105Fa09-XXX/PDF/105Wed11-4-09.pdfChem 105...
Transcript of Chem 105 Wednesday 4 Nov 2009chem.uaf.edu/keller/Courses/105Fa09-XXX/PDF/105Wed11-4-09.pdfChem 105...
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Chem 105 Wednesday 4 Nov 2009
1) Review schedule2) Review electron configurations3) “spdf” and “orbital box” notations4) Electron configurations are the basis for Periodic Table structure5) Configurations of ions6) Trends in atom size (atomic radius)
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Write this scheme out by Write this scheme out by Write this scheme out by Write this scheme out by hand to remind yourself!hand to remind yourself!hand to remind yourself!hand to remind yourself!
etc
(Please remember this order)
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How many p-electrons are in a nitrogen atom?
zero
One
Two
Thre
e
Four
Fiv
e
Six
1% 3% 4%
10%
4%4%
72%1. zero
2. One
3. Two
4. Three
5. Four
6. Five
7. Six
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In a multi-electron atom, the nuclear charge is partially “shielded” or “neutralized” by electrons with lower n or l values. Therefore s-electrons feel a greater “effective nuclear charge”.
http://winter.group.shef.ac.uk/orbitron/
2s-electrons “penetrate”through to the nucleus more than 2p-electrons do,
Actually, the average distance of 2s and 2p is the same.
Radial distribution of electrons in 2s and 2p orbitals
…but the s- and p- energies differ in a multi-electron atoms because the “radial distribution” differs:
r
e- probability
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Hydrogen atom Multi-electron atom
S,p,d subshells have different energies because these s-electrons“penetrate” through toward the nucleus more than p-electrons, and p more than d …
S-electrons
“feel” the
greatest
nuclear charge.
So, the energy
of s-orbitals
decrease the
most in larger
atoms.
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What is the electron configuration of a technecium atom (Tc)?
Atomic # = 43, therefore 43 e-
1s22s22p63s23p63d104s24p64d55s2
Check sum electrons:2+2+6+2+6+2+10+6+5+2=43
The “spdf” notation for electron configuration follows the convention of writing orbitals in order of increasing n. (This is not necessarily the filling order.)
Noble gas notation = [Kr] 4d55s2
2
10
18
30
20
36
38
43
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Box notation for technecium (Tc) atom
[Kr]
5s4d
What is one correct set of four quantum numbers (n, l, ml, ms) for this electron?
n = 4l = 2 (it is a d-orbital)m
l= +2 (or +1, 0, -1, -2. There is no necessary label on each box)
ms = +1/2 (or -1/2. Up or down are arbitrary for a given single electron)
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Periodic table is organized on the basis ofwhich subshell contains the atom’s outermost electrons.
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21 Sc [Ar]3d14s2
22 Ti [Ar]3d24s2
23 V [Ar]3d34s2
24 Cr [Ar]3d54s1
25 Mn [Ar]3d54s2
26 Fe [Ar]3d64s2
27 Co [Ar]3d74s2
28 Ni [Ar]3d84s2
29 Cu [Ar]3d104s1
30 Zn [Ar]3d104s2
This is due to another effect, namely the stabilization offered by a half-filled or full subshell.
Table 7.3
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Please learn and remember the electron configurations of all main group atoms plus 1st row of transition metals
Lower d-block and f-block atoms contain more slight inconsistencies due to very close orbital energies.
2 exceptions
Cr Cu
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The “valence shell” of an atom contains all the electrons
with highest n-value. How many electrons are in the
valence shell of silicon (Si) atom?
one
two
thre
e
four si
x
6%
53%
1%
26%
13%
1. one
2. two
3. three
4. four
5. six
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1. 12. 23. 34. 45. 6
[Ne]3s23p2
4 electrons in Si atom have n = 3, which is the highest n-value (of electrons in this atom).
The “valence shell” of an atom contains all the electrons with highest n-value. How many electrons
are in the valence shell of silicon (Si) atom?
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In a Stern-Gerlach experiment using silicon atoms, they will fly straight through without deflecting.
Tru
e
False
72%
28%
1. True2. False
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In a Stern-Gerlach experiment, silicon atoms will fly straight through without deflecting.
1. True2. False
(Silicon atoms will be deflected. They contain 2 unpaired electrons, which makes the atom paramagnetic.)
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Electron configurations of main cations are just the smaller noble gas..
Ba atom is [Xe] 6s2
Ba2+ is [Xe]
O atom is [He] 2s22p4
O2- ion is [Ne]
Electron configurations of main anions are just the larger noble gas..
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Transition metal atoms always lose outer shell s electrons first.
Fe atom is [Ar] 3d6 4s2
3d 4s
Fe3+ ion is [Ar] 3d5
3d 4s
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Measuring “magnetic susceptibility”. Paramagnetism depends on number of unpaired electrons.
On a per-atom basis, Fe3+ ions are more magnetic than Fe atoms, since each Fe3+ ion contains 5 unpaired electrons, whereas Fe atoms contain only 4.
(This ignores the possibility of “ferromagnetism” which iron metal and several other transition metals sometimes achieve – and is way stronger than paramagnetism.)
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Atomic Radius
- Measured in picometers (pm) 1 pm = 10-12 mor Angstroms (Å) 1 Å = 100 pm = 10-8 cm
- Generally increase going down a group (down a column) and decrease going across a period (L-to-R in a row)
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The problem with the term “Atomic Radius” is that the numbers differ depending on how it is obtained!
- “covalent radius” = half distance between bonded atoms
or
- “calculated radius” = distance out to arbitrary electron density based on quantum mechanics calculation (Schrodinger equation)
or
- “experimental” based on crystal of metal atoms = ½interatomic distance
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0.0001 e-/Å3 contour
0.0448 e-/Å3
We define the “calculated atomic radius” = distance from nucleus out to electron density ~ 0.05 e-/Å3
Electron distribution in H atom/H2 molecule system