Question

Why is atomic number considered to be a more appropriate parameter than atomic mass for the classification of elements in a periodic table? How does the metallic character of elements vary as we move (i) from left to right in a period, and (ii) top to bottom in a group in the modern periodic table? Give reasons to justify your answers.

 

 

Answer 1

The atomic number is considered to be more appropriate parameter for the classification of elements than atomic mass because atomic number is equal to the number of electrons in an neutral atom, and the arrangement of electrons in an atom gives its electronic configuration. Thus, when elements are arranged in the order of increasing atomic number, then elements with similar electronic configuration occur together. These elements have similar chemical properties, which explains the periodicity in modern periodic table.

Metallic character: It is defined as the tendency of an atom to lose electrons.

Across the period i.e., from left to right: Metallic character decreases.

Down the group i.e., from top to bottom: Metallic character increases.

Reason: Across the period, the effective nuclear charge increases, thus decreasing its atomic radius. This favours the increase of electronegativity and therefore, the tendency to lose electrons is low. This accounts for the decrease in the metallic character along the period. But as we move down the group, the number of shells keep on increasing and therefore, the atomic size increases. This means that the electronegativity decreases. This enhances the ability to lose electrons and therefore, the metallic character increases down the group.