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 + )