Biological importance of Na and K
i) Sodium ions participate in the transmission of nerve signals.
ii) Sodium ions also regulate flow of water across the cell membranes and in transport of sugars and amino acids into the cells.
iii) Potassium ions are the most abundant cations within cell fluids, where they activate many enzymes, participate in oxidation of glucose to produce ATP.
iv) Potassium ions in combination with sodium ions are responsible for transmission of nerve signals.
v) The functional features of nerve cells depend upon the sodium potassium ion gradient that is established in the cell.
Group 2 elements: Alkaline earth metals
( a) Atomic radii: The atomic radii of alkaline earth metals are fairly large though smaller than the corresponding alkali metals and they increase down the group. This is because on moving down the group, atomic radii increase primarily due to the addition of an extra shell of electrons in each succeeding element.
( b) Ionic radii: the atoms of these elements form divalent ions which show the same trend of increase in their size down the group.
( c) Ionization enthalpy: The alkaline earth metals have fairly low Ionizations enthalpies though greater than those of the corresponding elements of group 1 and this value decreases down the group.
( d) Hydration enthalpy: The Hydration enthalpies of alkaline earth metal ion decrease as the size of the metal ion increases down the Group Be 2 + > Mg 2 + > Ca 2 + > Sr 2 + > Ba 2 +
( e) Oxidation State: All the members of the family exhibit + 2 oxidation state in their compounded and the form divalent cations( M 2 +)