Understanding Points
Structure 2.3.1—A metallic bond is the electrostatic attraction between a lattice of cations and
delocalized electrons.
Structure 2.3.2—The strength of a metallic bond depends on the charge of the ions and the radius of the metal ion.
Metallic bonding
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The electrostatic attraction between a lattice of positive ions and delocalized electrons
•
Factors that affect size of electrostatic attraction:
1.
No. of delocalised e-s
2.
Charge of ion
3.
Ionic radius of cation
•
Reflected back in periodicity topic where strength of metallic bond
◦
↓ Down group, ↑ Across period (1 to 13)
Physical properties of metals/metallic compounds
good electrical conductivity | delocalized electrons are highly mobile, and so can move through the metal structure in response to an applied voltage | Electrical circuits use copper |
good thermal conductivity | delocalized electrons and close packed ions enable efficient transfer of heat energy | Cooking equipments |
malleable
(ability to form thin sheets) | Conformation changes under applied pressure
“Layers slide over each other”
*movement of delocalized electrons is non-directional and essentially random through the cation lattice, so the metallic bond remains intact | Moulded into many forms machinery and structural components of buildings and vehicles |
ductile
(ability of material to deform under stress) | Electric wires and cables | |
high melting points/hard, strong | a lot of energy is required to break the strong metallic bonds and separate the atoms | High speed tools and turbine engines; tungsten has the highest melting point |
shiny, lustrous appearance | delocalized electrons in metal crystal structure reflect light | Ornamental structures, jewelry |
2.3 The metallic model (AHL)
Understanding points
Structure 2.3.3—Transition elements have delocalized d-electrons. (AHL)
Transition metals
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Have incomplete d orbitals in one or more of their oxidation states
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Lose their (n)s electrons before (n-1)d electrons
•
This means transition metals have more e-s available to become delocalized
→ Greater e- density → stronger electrostatic forces → high melting point
→ Large number of delocalized e-s → good electrical conductivity