2.3 The metallic model
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What is a metallic bond?
Electrostatic attraction between a lattice of cations and delocalised electrons
What is the ionisation energy of metals usually?
Low
What occurs in the metallic bonding model?
Valence electrons become delocalised Resulting metal cations are densely packed in a lattice Delocalised valence electrons spread tehemselves out throughout metallic lattice (sea of delocalised electrons)
What are the properties of metals?
lustruous malleable ductie high boiling point (often high melting point) dense good head nad electricity conductors
Why are metals good conductors of electricity when solid and molten?
Delocalised electrons are free to move if source of electric current is attached. Can flow from negative to positive electrode
Why are metals good conductors of heat?
When heated, the kinetic energy of delocalised electrons is increased and rapidly distributed through the lattice. Increased lattice vibrations also pass energy on from one densely packed metal cation to the next
Why are metals malleable and ductile?
Layers of cations can be forced across each other. Delocalised electrons can move to compensate for this and re-establish electrostatic forces
What does malleable mean?
Able to be bent into a sheet
What does ductile mean?
Able to be bent into a wire
Why do metals have high boiling points?
Large amounts of heat energy are required to overcome the strong electrostatic forces of attraction between cations and delocalised electrons
Why are metals lustruous?
delocalised electrons reflect light
Why do metals have high densities usually?
Closely packed in lattice -> high mass per unit volume
What does more crystals mean for the brittleness of the metal?
More brittle
What does the strength of the metallic bonding depend on?
Radius of a metal ion Charge of a metal ion
What happens to the metallic bonding strenght as it goes down Group 1?
Decreases
Why does a small ionic radius lead to strong metallic bonding?
The smaller the ionic radius, the stronger the electrostatic attraction between lattice of positive cations and sea of negative delocalised electrons, and thus stronger metallic bonding
What is charge density?
Ratio of charge to volume of an ion
Why does the strenght of metallic bonding increase with increasing charge on the metal ion?
For ions of similar radius, greater charge leads to greater charge density, leads to stronger electrostatic attraction between lattice of positive cations and sea of delocalised negative electrons, thus stronger metallic bonding
What are alloys?
Mixture of a metal with one or more elements, that retain the characteristics of a metal
Why are alloys made?
To enhance properties of the metal, such as Increased hardness Improved corrosion resistance Variation in colour Lower melting point
How are alloys generally prepared?
Mixing molten liquid metals or dissolving a solid in a molten metal
What is a substitutional alloy?
Alloy where the atoms have similar ionic radii so they can be substituted for each other in a lattice
What is an interstitial alloy?
Alloy where atoms are of different sizes, thus fitting in between each other.
What is a homogeneous alloy?
Atoms of different elements distributed uniformly