Metallic Bonding Flashcards
Do metals have high or low electronegativity?
Low and therefore they tend to lose their valence electrons
What is the structure metals make
Metallic lattice Structure
Explain the structure of a metallic latice
a metallic lattice comprises of an array of metallic cations fixed in a lattice structure and their valence electrons are able to move freely around the lattice structure
What are delocalised electrons
Electrons in a metallic bond that are able to move freely around the structure
What holds the metallic structure together
The electrostatic attraction between the cations and the delocalised electrons keep the lattice stable and strong
Explain the following property of metals: lustre
This is due to the mobile electrons able to reflect light causing the metal to shine
Explain the following property of metals: conduction of heat
The electrons are able to receive kinetic energy in hotter areas of the metal and they transfer this heat by hitting neighbouring electrons
Explain the following property of metals: conduction of electricity
As the electrons can carry an electric current down the metal. When a electric field is applied the free electrons move to the positive end of the metal
Explain the following property of metals: malleability and ductility
As the attractive forces made by the cations extend in all directions the layers of atoms can slide past one another without disrupting the lattice structure
Explain the following property of metals: melting point
As the bond is very strong it requires a lot of energy to break the bonds, the more valence electrons the harder the bond
Explain the following property of metals: density
As the lattices are closely packed
Explain the ball bearing model
A metal with perfect rows of atoms will bend easily however if they are distorted it is harder to bend
Metals do not crystallise in perfect rows, but the form areas of perfect close packing atoms called grains. The areas around where the grains meet are called grain boundaries.
It is the grains that are arranged irregularly
Therefore: metals with larger grains have fewer dislocations and Ben easily
Metals with small grains have many dislocations and don’t bend easily
List the methods of modifying metals
Work hardening
Annealing
Quenching
Tempering
Explain work hardening
Occurs when the metal is hammered and causes smaller grains and is harder to bend but is harder, they are brittle as there are more dislocations
Explain annealing
Metals are heated until red hot then are cooled slowly.
Larger metal grains will form so the metal will be softer and more ductile
Explain quenching
Metals are heated until red hot the are cooled quickly in ice water
Smaller grains are formed which makes the metal harder and more brittle
Explain tempering
The metal is first quenched then heated again but able to be cooled slowly
This reduces the brittleness of the substance while retaining the hardness
What is an alloy
When a metal is mixed with another metal or non metal to create different properties
What is a substitutional alloy
When atoms are alloyed are the same size they replace each other in the crystal structure
What is an interstitial alloy
When atoms of different sizes are alloyed, the smaller atom fits inside the spaces of the larger atoms lattice structure
List the property pies of metals
Lustrous - shiny when polished
Good conductors of heat and electricity
Malleable - can be hammered or bent into any shape
Ductile - can be drawn out into wires
High density
High melting points
Hard and have high tensile strength, high resistance to stress and do not easily break
