Some Other Periodic Properties

• Atomic Volume: Atomic volume increases in a group from top to bottom. The increase is due to the increases in the number of energy shells.

In period from left to right, atomic volume varies cyclically, i.e., it decreases at first for some elements, becomes minimum in the middle and then increases.

• Density: The density of the elements in solid state varies periodically with their atomic numbers. At first, the density increases gradually in a period and becomes maximum somewhere for the central members and then start decreasing afterwards gradually.

Li Bi C N O F

0.5 1.8 .3 2.2...

Na Mg Al Si P S Cl

1.0 1.7 2.7 2.3 1.8 2.1...

In solids Osmium has the highest density (22.6) & in liquid Hg has the highest density (13.6)

• Melting and boiling points: The melting points of the elements exhibit some periodicity with rise of atomic number. It is observed that elements with low values of atomic volumes have high melting point while elements with high values of atomic volumes have low melting points. In general, melting points of elements in any period at first increases and become maximum somewhere in the centre and thereafter begins to decreases

Li Be B C N O F Ne

181 1277 2030 3727 -210 -219 -220 -249

Na Mg Al Si P S Cl Ar

98 650 660 1410 44 119 -101 -189

• Nature of oxides: In a period, from left or right the basic nature of the oxides decreases while acidic nature of the oxides increases. Down the group, basic nature increases or acidic nature decreases. Oxides of the metal are generally basic and oxides of the non-metals are acidic or neutral. The oxide of the metalloids are generally amphoteric, The oxide of Al, Zn, Sn, As and Sb are amphoteric. We can summarize that as the electronegativity of element increases, acidic character of oxides increases. In general oxide of higher oxidation states of same elements are acidic and lower oxidation states are basic.
• Nature of oxy – acids: In a period, the strength of the oxy – acids formed by non – metals increases from left to right

In a group, the strength of the oxy – acids of non – metals decreases

• Nature of hydrides: The nature of the hydrides changes from basic to acidic in a period from left to right.

In a group, the acidic nature of the hydrides of non metals increases. The reducing nature also increases but stability decreases from top to bottom.

HF HCl HBr HI

• strength of the acid increases
• stability decreases
• reducing nature increases

Effective Nuclear Charge and Shielding Effect:

• In a multielectronic atom, the effect of nuclear charge experienced by the outermost electron is less than the theoretical value of the nuclear charge (Z).
• If the nuclear charge of an atom is Z, effective nuclear charge is Zeff and shielding constant is σ then according to Slater

Zeff = Z –σ

DIAGONAL RELATIONSHIP

Elements of second period Li, Be and B resemble closely with the elements Mg, Al and Si of third period in the next higher group.

Diagonal relationship is due to similar size of ions and almost similar electronegativities of the elements or more correctly is due to similar polarizing power of ions (ionic charge/ionic radius2).

Diagonal relationship is predominant only in lighter non-transition elements.