A quantitative measure of the tendency of an element to lose electron is given by its ionisation enthalpy (I.E.).
I.E. increases from left to right in a period of the periodic table. However, in second period, the I.E of oxygen is less than that of nitrogen. Why?

Why does the first ionization enthalpy increase as we go from to across a given period of the Periodic Table?

The reactivity of an element is very much related to its ionization enthalpy. In general, ionization enthalpy increases from left to right across a period. Give the reason.

The first ionisation enthalpies of second period elements generally increase from left to right along the period. Give reason for this general trend.

Name of elements with atomic numbers greater than 100 are given by IUPAC the first inoisation enthalpies of second period element generally increase from lewft to right along the period. Give reason for this general trend.

The statement that is not correct for the periodic classification of elements is The properties of elements are periodic functions of their atomic numbers. Non-metallic elements are lesser in number than metallic elements. Electronegativity of the elements along the period from left to right increases in a regular manner. For transition elements the d-subshells are filled with the electrons monotonically with increase in atomic number.

The formation of chemical compounds takes place as a result of combination of atoms of various elements. Explain how ionization enthalpy (I.E) and electron gain enthalpy (E.G.E) determine whether atoms of elements will combine to form ionic compounds.