Chemistry · D And F Block Elements · NEET
Transition metals all have almost the same atomic size (metallic radii close to each other) and similar metallic bonding. NCERT says alloys form when the metal radii are within about 15% of each other. Since transition metal atoms sit next to each other in the periodic table and their sizes are very close, one metal's atoms can easily replace or mix with the other's atoms in the crystal. This is why they blend readily to form alloys.
NCERT states that a homogeneous (substitutional) alloy forms when the two metals have metallic radii within about 15% of each other. If the sizes are that close, the atoms of one metal can take the place of the atoms of the other in the crystal without breaking the structure. Because transition metals have such similar radii, they easily satisfy this 15% condition and form alloys.
In an alloy, the second metal's atoms are similar in size and REPLACE the host metal's atoms in the crystal (a solid solution of metals). In an interstitial compound, small non-metal atoms like H, C, or N are TRAPPED in the tiny empty spaces (interstices) between the big metal atoms. Simple rule: alloy = metal + metal (similar sizes), interstitial compound = metal + small atom (H, C, N) sitting in gaps.
When atoms of a second metal (of slightly different size) enter the crystal, they distort the neat rows of atoms. This makes it harder for atomic layers to slide over each other, so the alloy becomes harder and stronger. NCERT also notes alloys of transition metals often have high melting points because of strong metallic bonding. This is why steel is much harder than pure iron.
An alloy is a mixture, not a true compound. NCERT calls it a blend of metals prepared by mixing the components, often a homogeneous solid solution. The metals are not joined in a fixed whole-number ratio like in a compound, so the composition can vary. In solution terms an alloy is a solid dissolved in a solid (solid solution).
Identify the incorrect statement.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Brass is an alloy of copper and zinc (Cu + Zn). Bronze is an alloy of copper and tin (Cu + Sn). Both are important industrial alloys and both are named in NCERT.
NCERT names chromium, vanadium, tungsten, molybdenum and manganese as transition metals added to iron to make different steels and stainless steel. These make the steel harder and more resistant to rust.
Yes. NCERT gives brass (copper with zinc) and bronze (copper with tin) as examples of transition metals forming alloys with non-transition metals. These are of great industrial importance.
Alloy formation is one of the general properties of transition metals in the d- and f-block chapter. NEET often asks it together with interstitial compounds, catalytic activity and variable oxidation states as 'correct/incorrect statement' questions, so knowing the 15% rule and examples earns easy marks.
An alloy is a solid solution, specifically a solid dissolved in a solid. NEET 2025 (Solutions chapter) matched 'Alloys' with 'Solid in solid'. Amalgams (alloys with mercury) are the liquid-in-solid case.
