Electronic structure

1. ELECTRONIC STRUCTURE ELECTRONIC STRUCTURE
AND THE PERIODIC LAWAND THE PERIODIC LAW
Dr Sharipah Ruzaina Syed ArisDr Sharipah Ruzaina Syed Aris
srsa_july2009

2. The distribution of electrons
among the orbitals of an atom
is called the electronic
structure or electronic
configuration
srsa_july2009

3. To indicate the ground state electron
configuration we can:
1)List the subshells that contain electrons and
indicate their electron population with a
superscript.
2) Represent each orbital with a circle and use
arrows to indicate the spin of each electron.
Electron configurations must be
consistent with the Pauli principle, aufbau
principle, and Hund’s rule
Example: N 1s
2
2s
2
2p
3
, Na 1s
2
2s
2
2p
6
3s
1
srsa_july2009

4. Electron configurations explain the
structure of the periodic table
The periodic table is divided
into regions of 2, 6, 10, and 14
columns which is the
maximum number of electrons
in s, p, d, and f sublevels.
Subshells that fill across the
periods.
srsa_july2009

5. For the representative elements (A
Groups) the electrons with the highest n
value or valence shell are normally the
only electrons important for chemical
properties
For these elements the valence
electrons consist of just the s and p
subshells encountered crossing the period that
contains the element in question
Example: the valence configuration of bromine is
Br 4s
2
4p
5

srsa_july2009

6. There are few important exceptions to the
“expected” electronic figurations of
commonly encountered elements
Following the rules for Cr, Cu, Ag, and Au
using noble gas notation:
11029
11029
11029
1524
6[Xe]5 6[Xe]5Cu
5[Kr]4 5[Kr]4 Ag
4[Ar]3 4[Ar]3Cu
4[Ar]3 4[Ar]3Cr
alExperiment ExpectedElement
sdsd
sdsd
sdsd
sdsd
srsa_july2009

7. Illustrating Orbital Occupancies
The electron configuration
nl
#of electrons in the sublevel
as s,p,d,f
The orbital diagram (box or circle)
Order for filling energy sublevels with
electrons
srsa_july2009

8. dark - filled, spin-paired
light - half-filled
no color-empty
A vertical orbital diagram for the Li ground state
srsa_july2009

9. srsa_july2009

10. Condensed ground-state electron configurations in
the first three periods.
srsa_july2009

11. srsa_july2009

12. srsa_july2009

13. A periodic table of partial
ground-state electron
configurations
srsa_july2009

14. PERIODIC TRENDS PERIODIC TRENDS
IN IN
ATOMIC PROPERTIESATOMIC PROPERTIES
*size*size
*Ionization energy*Ionization energy
*electron affinity*electron affinity
srsa_july2009

15. Variation in atomic and ionic radii. Values
in picometers (10
-12
m)
srsa_july2009

16. The size trends in ions can be summarized:
◦Positive ions are always smaller than the atoms
they are formed
◦Negative ions always larger than the atoms
from which they are formed
Adding electrons leads to an increase in
size of a particle, as illustrated for
fluorine. Removing electrons decreases
the size of the particle, as shown for
lithium and iron.
srsa_july2009

17. Ionization energy (IE) is the energy
required to remove an electron from an
isolated, gaseous atom
Successive ionizations are possible until no
electrons remain
The trends in IE are the opposite of the
trends in atomic size
-+
+® egXgX )()(
srsa_july2009

18. Periodicity of first ionization energy (IE
1
)
srsa_july2009

19. Variations in first
ionization-energies.
Elements with the
largest ionization
energies are in the
upper right of the
periodic table.
Those with the
smallest ionization
energy are at the
lower left.
srsa_july2009

20. Ranking Elements by First Ionization Energy
PLAN:
SOLUTION:
PROBLEM: Using the periodic table only, rank the elements in each of the
following sets in order of decreasing IE
1
:
(a) Kr, He, Ar(b) Sb, Te, Sn (c) K, Ca, Rb (d) I, Xe, Cs
IE decreases as you proceed down in a group; IE increases as you
go across a period.
(a) He > Ar > Kr
(b) Te > Sb > Sn
(c) Ca > K > Rb
(d) Xe > I > Cs
Group 8A(18) - IE decreases down a group.
Period 5 elements - IE increases across a period.
Ca is to the right of K; Rb is below K.
I is to the left of Xe; Cs is furtther to the left and
down one period.
srsa_july2009

21. The electron affinity (EA) is the potential
energy change associated with the addition
of an electron to a gaseous atom or ion in
its ground state
The addition of one electron to a neutral
atom is exothermic for nearly all atoms
The addition of more electrons requires
energy
)()( gXegX
--
®+
srsa_july2009

22. Electron affinities of the main-group elements.
srsa_july2009

23. In general:
◦EA increases from left to right in a period
◦EA increases bottom to top in a group
srsa_july2009

24. Trends in three atomic properties.
srsa_july2009

25. srsa_july2009
Which has the larger second ionization
energy?
lithium or beryllium
Why?

26. srsa_july2009
Arrange the elements oxygen, fluorine,
and sulfur according to increasing
◦ Ionization energy
◦ Atomic size