Page 260 - Instant notes

G7
CHEMICAL AND STRUCTURAL
EFFECTS OF QUANTIZATION

Key Notes
The structure of the periodic table reflects the ground state
electronic configuration of the elements according to the Aufbau
principle of allocating electrons to atomic orbitals in order of
increasing orbital energy. The elements are arranged in periods
such that every element in a group has the same configuration of
valence electrons in the outer shell. The analogous valence
configuration gives rise to the periodicity in physical and
chemical properties of the elements.
The atomic radius is a measure of the size of an atom. Atomic
radii decrease across a period, because of the increase in nuclear
charge and incomplete nuclear shielding, and increase down a
group, because successively larger principal shells are occupied.
The first (and second…) ionization energies are the minimum
energies required to remove the first (and second…) electrons to
infinite distance from the atom. Ionization energies generally
increase across a period, because the outer electron becomes
more tightly bound as nuclear charge increases, and decrease
down a group, because the outer electron occupies successively
larger orbitals more weakly bound to the nucleus.
An atomic transition is the movement of electron(s) between two
electronic configurations (or states). The difference in energy
between the two states determines the frequency of associated
radiation. Allowed atomic electronic transitions obey the
selection rule, ∆l=±1 and ∆m l =0, ±1.
The alkali metal atoms contain a single s valence electron outside
a closed core and are called hydrogen-like. The energy level
distribution in hydrogen-like atoms, and the pattern of the
emission spectra, closely resemble those of the hydrogen atom.
Related topics The structure of the hydrogen General features of spectroscopy
atom (G5) (I1)

Many-electron atoms (G6)