Post on 06-May-2018
10/28/2011 1
Chem 105 Friday 28 Oct 2011
1) Electron configurations of transition metal atoms2) Electron configurations of ions3) Trends in Periodic Table: atomic radius4) Ion size5) Ionization potential
6) Chap 8: Lewis formulas
10/27/2010 2
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
10/27/2010 3
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’s in 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)
10/27/2010 4
Periodic table is organized on the basis ofwhich subshell contains the atom’s outermost electrons.
10/27/2010 5
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 stabilization offered by a half-filled or full d-subshell.
Table 7.3
10/27/2010 6
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 with straight aufbau filling due to very close orbital energies.
Exceptions
Cr Cu
10/27/2010 7
The “valence shell” of an atom contains all the electronswith highest n-value.
How many electrons are in the valence shell of a silicon (Si) atom?
one
two
thre
e
four
six
2
57
7
3429
1. one
2. two
3. three
4. four
5. six
1 2 3 4 5 6 7 8 9 10 11 12 13
1
14
27
40
53
66
79
92
105
118
131
144
157
170
183
196
10/27/2010 8
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 a
silicon (Si) atom?
10/28/2011 11
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..
10/28/2011 12
Transition metal atoms always lose outer shell s electrons 1st.
Fe atom is [Ar] 3d6 4s2
3d 4s
Fe3+ ion is [Ar] 3d5
3d 4s
[Ar]
[Ar]
These go 1st.Then 1 of these (to maximize spin).
10/28/2011 13
The apparent paradox of “filling 4s first when making atoms”, but then “removing highest n-value first when making ions” is really due to the different effects the higher-charged nucleus has on orbitals in the ION vs orbitals in the ATOM. For example:
Cr atom is [Ar] 3d5 4s1
3d 4s
Fe2+ ion is [Ar] 3d6
3d 4s
[Ar]
[Ar]
These two particles both have 24 electrons, but Fe has 2 more protons in the nucleus, which changes the orbital energies in a way that disfavors the 4s orbital.
These different configurations can be compared computationally using quantum theory. In one calculation, the [Ar]3d6 configuration (4 unpaired e) of Fe2+ ion is 94 kcal/mol more stable than the [Ar]3d54s1 configuration (6 unpaired e).
10/28/2011 14
3d 4s
[Ar]
[Ar]
[Ar]
[Ar]
Calculated Fe2+ ion energies (gas phase)
123
64
94
0
Relative energy (kcal/mol)
B3LYP/6-31G*
10/28/2011 15
Measuring “magnetic susceptibility”. Paramagnetism depends on number of unpaired electrons. This is an experimental test for # of unpaired electrons.
Fe3+ is more magnetic than Fe2+. Fe3+ ions contain 5 unpaired electrons, whereas Fe2+ ions contain 4 unpaired electrons.
(This ignores the possibility of “ferromagnetism” which iron metal and several other transition metals sometimes achieve – and is way stronger than paramagnetism.)
10/28/2011 18
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)
10/28/2011 21
“Atomic Radius” values depend somewhat on method used.
- “covalent radius” = half distance between bonded atoms
or
- “calculated radius” = distance out to arbitrary electron density based on quantum mechanics calculation (Schrödinger equation)
or
- “experimental” based on crystal of metal atoms = ½ interatomic distance
10/28/2011 22
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
10/28/2011 23
H-H dist = 74 pm
H covalent radius = 74÷÷÷÷2=37 pm
H2 molecule
H atom
Electron distribution in H atom/H2 molecule system
H atom radius = 44 pm
10/28/2011 24
Covalent radius is always smaller because electrons are pulled in by the extra attractive force of the second nucleus in the molecule.
10/28/2011 26
Crystal structure (experimental) of metallic sodium.Na-Na distance = 365 pm; so, Na radius = 365/2 = 183 pm
365 pm
10/28/2011 27
Going from atom to atom DOWN a group, you add a complete shell of electrons plus the same number of protons in the nucleus.
4+2e-
--
Berylium atom(1s2 2s2)
12+2e-
--
8e-
Magnesium atom(1s2 2s2 2p6 3s2)
The nuclear charge increases by 8+, but this is counteracted by the complete inner shell of 8 electrons.The extra shell shields the outer shell electrons from the increased positive charge.
e- in 2s orbitale- in 1s orbital
2e- in 3s orbital
8e- in 2s,2p orbitals
10/28/2011 28
12+2e--
8e-
Magnesium atomr = 145 pm
- 13+2e-
-
8e-
Aluminum atomr = 118 pm
-
-
14+2e-
-
8e-
Silicon atomr = 111 pm
-
--
The situation is different going ACROSS a row Left-to-Right.
In this case, electrons are added to the same shell - on the periphery of the atom, and the # of inner-shell electrons is constant.
The outer-shell electrons DO NOT shield each other from the increasing nuclear charge because they are spread out with approximately same average distance from the nucleus.
Place the following atoms in order of increasingatomic radii: S, Se, Cl , As
10/28/2011 30
Cl <
S <
Se
< ...
S <
Cl <
As <
...
S <
Cl <
Se <
...
As <
Se<
S < C
... S
e <
As <
S < ..
.
88
18
387
1. Cl < S < Se < As2. S < Cl < As < Se3. S < Cl < Se < As4. As < Se< S < Cl5. Se < As < S < Cl
1 2 3 4 5 6 7 8 9 10 11 12 13
1
14
27
40
53
66
79
92
105
118
131
144
157
170
183
196
10/28/2011 32
Sizes of Ions
Cations (remember ca + ion)always SMALLER than corresponding atom (you’re removing electrons – usually a whole shell - without changing nuclear charge)
Anions Always LARGER than corresponding atom (you’re adding electrons – to complete a shell usually – without increasing the nuclear charge.)