Why melting point falls regularly as the atomic number increases ?!.. Why there is a sudden down fall in melting point of Mn & Tc ?!..
[Answer both questions here..as they are inter-related.]
Dear Student,
High melting point of transition metal series is due to the formation of metallic bonding.The strength of metallic bonding depends upon the number of unpaired electrons. On moving from left to right, number of unpaired electrons first increases leading to greater metallic bonding and hence higher melting point. Now, as the number of unpaired electrons starts decreasing, melting point also starts decreasing.
Zn has the lowest melting point as here all the electrons are paired so no metallic bond is formed.
Mn on the other hand has higher number of unpaired electrons yet it has low melting point. This can be explained on the basis of half filled d-orbital and fully filled s orbital which results in stable electronic configuration. Therefore, electrons are held tightly and there is less delocalisation of electrons which makes metallic bonding weaker.
High melting point of transition metal series is due to the formation of metallic bonding.The strength of metallic bonding depends upon the number of unpaired electrons. On moving from left to right, number of unpaired electrons first increases leading to greater metallic bonding and hence higher melting point. Now, as the number of unpaired electrons starts decreasing, melting point also starts decreasing.
Zn has the lowest melting point as here all the electrons are paired so no metallic bond is formed.
Mn on the other hand has higher number of unpaired electrons yet it has low melting point. This can be explained on the basis of half filled d-orbital and fully filled s orbital which results in stable electronic configuration. Therefore, electrons are held tightly and there is less delocalisation of electrons which makes metallic bonding weaker.