Periodic Patterns in the Main-Group
Elements: Bonding, Structure,
Electron configuration, atomic size, ionization energy, and electronegativity.
The principal quantum number n is related to the size and energy of the orbital. The azimuthal
quantum number l gives the shape of the orbital. The superscript tells the number of electrons
in the subshell.
The value of n.
In a group, n varies. Across a period, the number of electrons varies.
The number of valence shell electrons is given by the "old" group number, or by the "new"
group number minus ten.
increases across a period and decreases down a group.
As you move to the right across a period, the atomic size decreases, the IE
increases and the
EN increases, all as a result of the increased
ICl is polar; Br
is non-polar. The electronegativity of Cl is greater than that of I, so the I end
of ICl will be partially positively charged due to the greater "pull" of the Cl on the shared
ICl will have a higher boiling point than Br
since dipole-dipole forces in ICl are greater than
dispersion forces in Br
As an atom becomes smaller, its electrons are closer to the nucleus and are therefore more tightly
held, therefore increasing the ionization energy. The two trends are opposite to one another.
In general, stronger bonds (higher bond energy) are also shorter and less reactive. (This assumes
the same number and type of bonds.)
They are similar in that they involve sharing of electrons between atoms. They are different in that
covalent bonding includes sharing between a small number (usually two) of atoms, while metallic
bonding involves essentially all the atoms in a given sample.
The bonding would change from metallic to (perhaps) very polar covalent to ionic as the "other"
element went farther to the right. The electronegativity, ionization energy, and electron affinity all
change as you move to the right. The atomic properties of the leftmost element and the "other"
element become increasingly different, causing the type of bonding to change in response.
A pair of atoms bonded only by a single bond use a
bond, which is cylindrically symmetric; i.e.,
its energy will not change significantly with rotation. The "second" bond of the double bond is a
bond, which needs to be in a specific geometric orientation to form. Rotation of the molecule
about this bond would break this
bond, a process that requires more energy than is available
under ordinary circumstances.
The elements at the left (metals) form cations, which are smaller than the corresponding atoms;
the elements at the right (nonmetals) form anions, which are larger than the corresponding atoms.