In 1871, a Russian Chemist, Dimitri Mendeleev, gave a useful scheme for classification of elements. He presented the first regular periodic table in which elements of similar chemical properties were arranged in eight vertical columns called groups. The horizontal rows of table were called periods. He arranged elements in ascending order of their atomic masses and found that elements having similar chemical properties appeared at regular intervals. This observation was called Periodic Law.
Polarity is classified by the difference in two or more atoms that is the electronegativity value (EN)
En for Fluorine =4.0, Bromine=2.96 Chlorine =3.16 Hydrogen=2.1
for the molecules
HF=4.0-2.I=1.9
HCl=3.16-2.1=1.06
Hbr=2.96-2.1=0.86
Hi=2.66-2.1=0.56
H2=2.1-2.1=0
from the EN value above HF has the mast highest value of EN hence it is the most polar.
Continental air masses are characterized by dry air near the surface while maritime air masses are moist .Polar air masses are characterized by cold air near the surface while tropical air masses are warm or hot. Arctic air masses are extremely cold.
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