Chemistry · D And F Block Elements · NEET
In a metal, atoms are held together by metallic bonding — a shared sea of free electrons that glues the positive metal ions together. In transition metals, both the outer ns electrons AND the inner (n-1)d electrons take part in this bonding. Because more electrons are available, the metallic bond is very strong. A stronger bond needs more heat energy to break, so the melting point is high. NCERT states this directly: the high melting points are due to the involvement of a greater number of electrons from (n-1)d in addition to the ns electrons in the interatomic metallic bonding.
Both. In s-block metals like sodium, only the outer ns electron is free to bond, so their melting points are lower. In transition metals, the (n-1)d electrons are close in energy to the ns electrons, so the d electrons ALSO join the electron sea. This is the key point NEET tests: the extra (n-1)d electrons on top of the ns electrons make the bond strong. This is exactly the 'Reason' in the ReNEET 2026 assertion-reason question.
The strength of the metallic bond depends on how many electrons are available to bond. Going across a row, the number of these bonding electrons increases up to the middle of the series (around 5 or 6 d-electrons), so bond strength and melting point rise to a maximum near d5. After the middle, electrons start pairing up inside the d orbitals instead of staying free for bonding, so bond strength and melting point fall again as atomic number increases.
Mn is an anomaly. Its electron configuration is 3d5 4s2 — a half-filled 3d5 set that is very stable. Because this half-filled shell is stable, the d electrons are held tightly by the atom and are LESS available for metallic bonding. Fewer free bonding electrons means a weaker metallic bond, so Mn (and Tc in the 4d series) has an unexpectedly low melting point compared to its neighbours. NCERT calls these the 'anomalous values of Mn and Tc'.
Zn, Cd and Hg have a fully filled d10 configuration ((n-1)d10 ns2). Because the d subshell is completely full and stable, the d electrons do NOT take part in metallic bonding — only the two ns electrons do. With so few bonding electrons the metallic bond is weak, so these metals are soft, volatile and have very low melting points. Mercury (Hg) is a liquid at room temperature for this reason. These three are often not even called typical transition metals.
Roughly yes for the trend, but be careful. The melting point depends on how many electrons are FREE for metallic bonding, and unpaired d electrons contribute strongly. Maximum unpaired electrons occur near d5, which is why melting point peaks there. But once you hit a specially stable shell (half-filled d5 in Mn, or full d10 in Zn), those electrons get locked to the atom and stop bonding — so melting point drops. So it is about availability of bonding electrons, not a simple 'more unpaired = always higher' rule.
Assertion A: Generally, 3d transition metals have high melting points. Reason R: Involvement of 3d-electrons in addition to 4s-electrons in the interatomic metallic bonding. Choose the most appropriate answer:
The stability of Cu^2+ salts is more than Cu^+ salts in aqueous solution due to:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Tungsten (W), in the 5d series, has the highest melting point of all metals (about 3410 degrees C). This is because the 5d and 6s electrons give extremely strong metallic bonding.
The 4d and 5d electrons spread out more and overlap better, so they form even stronger metallic bonds than 3d electrons. That is why the melting points rise going down a group (for example 3d Cr < 4d Mo < 5d W).
Yes. Enthalpy of atomisation is the energy needed to break the metal into free atoms. Metals with strong metallic bonds (many bonding electrons) have both high enthalpy of atomisation and high melting points. They follow the same trend and peak near the middle of the series.
They have a full d10 configuration, so the d electrons do not join the metallic bonding. Only the two ns electrons bond, giving a weak lattice, so these metals are soft and low-melting. Mercury is even liquid at room temperature.
