Question

Element and Atomic Symbol Number Electronegativ (Pauling Scale Atomic Radius (pm) OR 10-12 m 186 Melting Point (C) 98 Boiling Point (°C) 883 11 0.9 12 160 649 1090 1.2 143 663 Sodium (Na) Magnesium (Mg) Aluminium (AI) Silicon (SI) Phosphorus (P) 2467 117 1410 2355 110 44 280 104 119 445 -101 -34 Sulfur (S) Chlorine (CI) Argon (Ar) 3.0 187 1 -189 -186

a) What trend in atomic radius is evident?

b) Identify this trend.

c) Would the same trend be observed for the period two elements?

Answer 1

The given elements are third period elements from Sodium to Argon.

a) The trend observed in the atomic radius is a gradual change from Sodium to Argon ie we move from left to right in the period in the periodic table.

b) The trend is identified as a gradual decrease in the atomic radius of the elements from Sodium to Argon ie we move from left to right in the period in the periodic table.

c) The same trend is also observed for the second period elements from Lithium to Neon.

REASON/EXPLANATION:

In the period we move from left to right in the periodic table, the atomic number increases but there is no increase in the shell number. If the atomic increases the nuclear charge increases gradually from one element to another element from left to right, hence the valency electrons are come closer to the nucleus. Therefore the atomic radius or atomic size of the elements gradually decreases from left to right in the period in the periodic table.