Chemistry · Periodic Classification Of Properties · NEET
Take a piece of solid metal, like copper. The atoms sit packed together and touch their neighbours. Pick two atoms sitting next to each other and measure the distance between their centres (nuclei). Now cut that distance in half. That half value is the metallic radius. NCERT defines it as half the internuclear distance separating the metal cores in the metallic crystal.
You cannot measure one single atom because an atom has no sharp edge. So scientists measure the distance between two neighbouring atoms in the solid metal using X-ray methods. Then they take half of that distance. Example from NCERT: two adjacent copper atoms in solid copper are 256 pm apart, so the metallic radius of copper = 256/2 = 128 pm.
Metallic radius = (distance between two neighbouring metal nuclei) / 2. In symbols, r = d/2, where d is the internuclear distance measured in the metal crystal. It is the same idea as covalent radius, just for metals instead of covalent molecules.
Both are half the distance between two like atoms. Covalent radius uses two atoms joined by a single covalent bond (example: Cl-Cl bond is 198 pm, so Cl covalent radius = 99 pm). Metallic radius uses two atoms sitting next to each other in a metal crystal (example: Cu is 128 pm). In a metal the bonding is weaker and more spread out, so metallic radius is usually a bit LARGER than the covalent radius of the same element.
The full distance you measure is from the centre of one atom to the centre of the next atom. That full distance covers the radius of atom 1 PLUS the radius of atom 2. Since both atoms are the same element and the same size, each atom's radius is exactly half of the whole distance. So you divide by 2.
Yes, mostly. NCERT says: for simplicity we use the term atomic radius to mean covalent radius for non-metals and metallic radius for metals. So when a NEET question says 'atomic radius' of a metal like Na, K, or Cs, it really means the metallic radius. The periodic trends (increases down a group, decreases across a period) apply to it.
In which of the following options the order of arrangement does NOT agree with the variation of property indicated against it?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. Metallic radius is measured from neutral metal atoms in a solid metal. Ionic radius is measured from ions (like Na⁺ or Cl⁻) in an ionic crystal. A cation is smaller than its parent atom, and an anion is larger.
Going down a group, a new electron shell is added at each step. More shells mean the outer electrons sit farther from the nucleus, so the atom (and its metallic radius) gets bigger. Example: Li < Na < K < Rb < Cs.
128 pm. The distance between two neighbouring copper atoms in solid copper is 256 pm, and half of that (256/2) is 128 pm.
No. Non-metals do not form metallic crystals, so we use covalent radius for them instead. Metallic radius is defined only for metals in the solid metallic state.
