(a) What are groups in the Modern Periodic Table? How do metallic character, atomic size, and valency differ within a group?

(b) An element has an atomic number of 14. Identify if this element is metallic or not. Give a reason to justify your answer.$=14$.

(a) The vertical columns present in the Modern Periodic Table having elements with similar vacancies and chemical properties are called Groups. For example, Alkali metals Group 1: H (Hydrogen), Li (Lithium), Na (Sodium), K (Potassium), Ru (Rubidium), Cs (Cesium), Fr (Francium). Valency: As we move down a group, valency remains the same, e.g. all alkali metals are monovalent. Atomic size: Atomic size is the distance from the center of the nucleus to the last shell. Metallic character: As we move down a group, the chemical reactivity of metals increases as it is easier for a bigger atom to lose electrons due to weaker electrostatic forces. But in non-metals, it decreases as it is easier for a smaller atom on top to gain electrons due to strong electrostatic forces than a bigger atom.

(b) Atomic number 
Electronic configuration $=2,8,4$
Element = silicon
This element has semi-properties of both metals and non-metals, so it is a metalloid. It has 4 valence electrons, due to which it can neither gain nor loss electrons as it would become unstable; hence it forms covalent bonds.