Download Chapter 7. Atomic Structure and Periodicity Part B. Definition and

Chapter 7. Atomic Structure and Periodicity
Part B. Definition and Reading
All orbitals with the same value of n have the same energy. The orbitals
are said to be degenerate.
Pauli exclusion principle
In a given atom no two electrons can have the same set of four quantum
numbers (n, l, ml, ms).
Since only two values of are allowed, an orbital can hold only two
electrons, and they must have opposite spins.
The electron is screened or shielded from the nuclear charge by the
repulsions of the other electrons.
The penetration effect causes an electron in a 2s orbital to be attracted to
nucleus more strongly than an electron in a 2p orbital. The 2s orbital is
lower in energy than the 2p orbitals in a polyelectronic atom.
Aufbau principle
As protons are added one by one to the nucleus to build up the elements,
electrons are similarly added to these hydrogen-like orbitals.
Hund’s rule
The lowest energy of configuration for an atom is he one having the
maximum number unpaired electrons allowed by the Pauli principle in a
particular set of degenerate orbitals.
Ionization energy is the energy required to remove an electron from a
gaseous atom or ion.
The first ionization energy increases when we go across a period from left
to right.
The first ionization energy decreases in going down a group.
Electron affinity is the energy change associated with the addition of an
electron to a gaseous atom.
In general, the electron affinities become more negative (exothermic)
from left to right across a period, there are several exceptions to this rule
in each period, which consider the change in electron repulsions as a
function of electron configuration.
When we go down a group, electron affinity should become more
positive (less energy released) since the electron is added at increasing
distances from the nucleus.
The atomic radii decrease in going from left to right across a period
because of the increasing effective nuclear charge. The valence electrons
are drawn closer to the nucleus, decreasing the size of the atom.
Atomic radius increases down a group, because of the increases in the
orbital size in successive principal quantum number n.