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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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11/4/2009 3

Thurs

Mon

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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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Monatomic ion charges

1+ 2+ 3+ 1-2-3-

2+variable

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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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Group 1 Alkali metals

Group 8A Noble Gases

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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

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H-H dist = 74 pm

H covalent radius = 37 pm

H2 molecule

H atom

Electron distribution in H atom/H2 molecule system

H atom radius = 44 pm