Inorganic chemistry
 Writing electron configurations and
orbital diagram.
 Atomic orbital shapes.
 1s orbital.
 2s orbital.
 Concept of hybridization.
Assistance Lecturer Amjad Ahmed Jumaa
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1
Writing electron configurations and orbital diagram:
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The electron configuration of an atom tells us how the electrons are distributed
among the various atomic orbitals. To write electron configurations, you should
follow the four rules or guidelines given below:
1-The electron configuration of all elements except hydrogen and helium are
represented by a noble gas core , which shows in (brackets) the noble gas
element that most nearly precedes the element being considered. The noble gas
core is followed by the electron configuration of filled or partially filled subshell
in the outermost shells.
2-The Aufbau or " building up " principle , states that electrons are added to
atomic orbitals starting with the lowest energy orbitals and " building up" to
higher
3-in many-electron atoms, the subshells are filled in order shown above.
4-each orbital can hold only two electrons.
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Example:
Write the ground-state electron configuration and the orbital diagram for selenium.
Solution:
Step (1): selenium has (34) electrons. These electrons need to be placed in atomic
orbitals.
Step (2): the noble gas element that most nearly proceeds (Se) is (Ar). Therefore, the
noble gas core is [Ar]. This core account for (18) electrons.
Step (3): the order of filling subshells past the (Ar noble gas core), you should find that
the order of filling is (4s , 3d, then 4p). there are (16) remaining electrons to distribute
among these orbitals.
The (4s) orbital can hold two electrons. Each of the five (3d) orbitals can hold two
electrons for a total of ten electrons. This leaves four electrons to fill the (4p)
Orbitals.
The electron configuration for (Se) is:
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[Ar] 4s23d104p4.
Step (4): to write an orbital diagram, we must also specify the spin of the
electrons. The (4s) and (3d) orbitals are filled, so the paired electrons in the (4s)
and in each of the (3d) orbitals must have opposite spins.
[Ar]
Step(5): now, let's deal with the (4p) electrons. Hund's rule states that most
stable arrangement of electrons in subshells is the one with the greatest number
of parallel spins. In the other words, we want to keep electrons unpaired if
possible with parallel spins. Since there are three (p) orbitals, three of the (p)
electrons can be placed individually in each of the (p) subshells with parallel
spins.
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Step (6): finally the fourth (p) electron must be paired up in one of the (4p)
orbitals. The complete orbital diagram:
Atomic orbital shapes:
1s orbital:
1-An s orbital l=0, has a spherical shape
2-the color shading is darker where the electron is more likely to be found.
1s orbital: the electron is most likely to be found near the nucleus.,
3-the electron has a 99% probability of being found.
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2s orbital:
1-The electron figure is likely to be found in two regions, one near the
nucleus, and the other in a spherical shell about the nucleus.
2-The 99% contour shows that the 2s orbital is larger than the 1s orbital
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Concept of hybridization:
 According to this concept, we may mix any number of atomic orbitals of
an atom, which differ in energy only slightly, to form a new orbitals called
hybrid orbitals, the mixing orbitals generally belong to the same energy level
(say 2s and 2p orbitals may hybridize).
 The total number of hybrid orbitals formed after mixing equals to the
number of atomic orbitals mixed or hybridized. The hybrid orbitals of an
atom shall have a maximum of two electrons
Thus hybridization precisely be defined as the phenomenon of mixing up(or
merging), of orbitals of an atom of nearly equal energy, giving rise to entirely
new orbitals equal in number to the mixing orbitals and having same energy
contents and identical shapes.
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