4.5 Metallic bonding
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Why are metals good conductors of heat and electricity?
Metallic ions have a sea of delocalized electrons which allow heat and electricity to be conducted
How are metal ions arranged?
Cations are arranged in a lattice structure
Metallic bond
Electrostatic attraction between lattice of positive metal ions and sea of delocalized electrons
Why is the force of attraction between metallic ions non-directional?
Because the force of attraction is in all directions. The electrons don’t “belong” to any atom
Why are metals malleable and ductile?
If sufficient force is applied, one layer of metal can slide over another without disrupting bond
How do metals pass electricity?
When voltage is applied, electrons are repelled from negative electrode and move towards positive electrode. This constitutes flow of an electric current
How is heat passed through metals?
Electrons move, carrying kinetic energy from hotter parts to colder parts of the metal
How do metals get their shininess?
Electrons reflect wavelengths of visible light
What does strength of bond depend on?
• Charge on metal ion 2. Ionic radius of ion
What can be used as an approximate measure for bond strength?
Melting point. Stronger bond = higher M.P.
Which has stronger metallic bond and explain why: • K (1+, ionic radius of 138 and melting point of 63.4C) • Ca (2+, ionic radius of 100 and melting point of 842C)
Calcium because: • Higher ionic charge= more delocalized electrons which increases forces of attraction • Smaller radius means more attraction between nuclei and electrons
How does ionic radius affect density of metals?
Decrease in radius means higher charge and hence higher density
Alloys
Homogenous mixtures composed of two or more metals or a metal and a non-metal
How do properties of alloys differ from those of pure metals?
• More corrosion-resistant • Stronger • Harder
What state do metals have to be in to make alloys?
Molten so that atoms can mix
Why are alloys hard?
Because there is addition of different sized atoms which means they cannot slide over each other
Are alloys more or less chemically stable than metals?
More chemically stable
Composition, properties and use of brass
• 70% copper and 30% zinc • Harder than copper • Used for musical instruments
Composition, properties and use of bronze
• 90% copper and 10% tin • Harder than copper • Used to make statues
Composition, properties and use of stainless steel
• 74% iron, 18% chromium, 8% nickel • More resistant to corrosion • Used in cutlery
Composition, properties and use of mild steel
• 99.7% iron and 0.3% carbon • Stronger and harder than iron • Used in construction
Composition, properties and use of solder
• 50% tin and 50% lead • Lower melting points • Used in electric circuit boards
Which has stronger London dispersion forces: C3H8 or C4H10?
C4H10 because it has higher molar mass so it has stronger forces
Which has stronger intermolecular forces: C3H8 or C2H4O?
C2H4O because even though they have same molar mass, C3H8 is non-polar while C2H4O is polar hence it can form dipole-dipole forces which are stronger