Physical properties of transition metals vs Group 1
Atomic structure and the periodic table • Properties of transition metals
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Key concepts
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Metallic bonding and electron structure
Metallic bonding arises from positive metal ions in a sea of delocalised electrons. Transition elements have partly filled d-orbitals that contribute additional delocalised electrons and stronger orbital overlap. Group 1 metals have a single outer s-electron that delocalises, producing weaker metallic bonds. Stronger metallic bonding in transition elements increases cohesion between atoms. Increased cohesion causes higher hardness, greater strength, higher melting points and larger densities compared with Group 1 metals, all else being equal.
Hardness and strength - definitions and causes
Hardness describes resistance to surface indentation or scratching; strength describes resistance to permanent deformation under load. Hardness and strength depend on bond strength, crystal structure and the presence of defects or impurities. Transition elements show higher hardness and greater strength because stronger metallic bonds require more energy to move dislocations and break atomic contacts. Group 1 metals are soft because weaker metallic bonding and larger atomic spacing allow layers of atoms to slide more easily.
Melting point - explanation and comparison
Melting point reflects the energy needed to overcome cohesive forces between atoms in the solid. Stronger metallic bonding and more electrons contributing to the bond raise the melting point. Transition elements have higher melting points than Group 1 metals because d-electrons increase bond strength and orbital overlap. Group 1 metals have low melting points because single s-electrons produce weaker metallic bonds and lower cohesive energy.
Density - atomic mass and packing
Density equals mass per unit volume and depends on atomic mass and how closely atoms pack in the crystal lattice. Transition elements often have higher atomic masses and similar or tighter packing than Group 1 metals. Higher atomic mass combined with relatively compact metallic structures causes transition elements to have greater densities. Group 1 metals have low densities because lower atomic masses and larger metallic radii reduce mass per unit volume.
Limiting factors and exceptions
Alloying, crystal defects, temperature and measurement conditions alter hardness, strength, melting point and density. Impurities and cold-working can increase hardness and strength by hindering dislocation motion. Some transition metals show lower-than-expected melting points or densities due to unusual crystal structures or low atomic mass among lighter transition elements (for example, some early transition metals). General trends remain reliable for typical comparisons with Group 1 metals.
Key notes
Important points to keep in mind