CBSE Class 10 Science 2017 · Paper 31/1 · Question 9

The Modern Periodic Table has 7 periods (horizontal rows) and 18 groups (vertical columns). (i) From left to right in a period, metallic character decreases. Across a period the electrons go into the same outermost shell while the nuclear charge increases, so the valence electrons are pulled in more strongly and the atoms get smaller; the tendency to lose electrons therefore decreases. In period 3, for example, sodium, magnesium and aluminium are metals, silicon is a metalloid, and phosphorus, sulphur and chlorine are non-metals. (ii) Down a group, metallic character increases. At each step down a new shell is added, so the atoms get larger and the valence electrons are farther from the nucleus; they are held less strongly and are lost more easily. In group 14, for example, carbon is a non-metal, silicon and germanium are metalloids, and tin and lead are metals.