Chapter 4 : Metallic Bonding Flashcards
Properties of metals
Lustrous Good conductors of heat/electricity Malleable Ductile Dense High melting/boiling points Hard High tensile strength
Metallic bonding
When metallic atoms bond to form a lattice, an array of cations surrounded by a sea of delocalised electrons
Why are metals lusterous?
The delocalised electrons in the lattice reflect light
Why are metals good conductors of heat?
Because the cations and delocalised electrons are mobile and therefore can “bump” together when heated and create more heat
Why are metals dense?
The metallic lattices are closely packed
Why do metals have high melting and boiling points?
The electrostatic attraction between a cation and delocalised electrons is really strong and increases up by atomic number
Why are metals good conductors of electricity?
The delocalised electrons are mobile and therefore an electrical is possible
Why are metals malleable and ductile?
The non-directional nature of metallic bonds
Layers of atoms can move past you without disrupting the force between the positive ions and the negative sea of electrons
Alloy
Mixing metals with other metals or non-metals to create an alloy which has specific properties, usually to mkae them stronger, flexible and light
Substitutional ally
If atoms that are being alloyed are about the same size they can replace the other in the metal crystal
Interstitial alloy
If the atoms being alloyed differ greatly in size the smaller atom may fit into the space between larger atoms
S block metal properties
Very reactive
Low density
Low melting points
D block metal properties
form colourful compounds
Iron, cobalt and nickel are magnetic
Useful catalyts
Limitations of the metallic bonding lattice model
Magnetism
Density
Malleability
Ball bearing model
Metals with large grains have fewer dislocation and bend easily
Metals with small grains have many dislocations and do not bend easily
A metal with perfect rows of atoms bend easily
If the rows are distorted they cannot slide over one another as easily and therefore do not bend as easily
Ways to modify a metal
Work hardening
Annealing
Quenching
Tempered
Work hardened metals
Bending or hammering metals create smaller crystal grains and making it stronger and harder to bend
More brittle
Annealed metals
Are heated and cooled slowly creating alrge crystal grains that are in perfect rows that bend easily and creating a softer metal
Used to restore ductility
Quenched metals
Heated and cooled instantly creating smaller crystals and the grains don’t have time to arrange in perfect rows so creating a harder brittle metal
Tempered metals
When quenched metals are heated again and allowed to cool slowly which reduces brittleness and retains hardness
Surface protection for metals
Plastic
Paint
Grease or oil
Metal coatings
Sacrificial coatings
Using a more reactive metal so that the coating will react with the environment not the metal
Galvanising
Noble coatings
Less reactive metal to cover the metal and that won’t be scratched or broken as breaking the coating will result in quick corrosion of the metal underneath
Used because they are usually harmless whereas more reactive tend to be harmful to people
Reaction with oxygen
Alkali metals
Metal + oxygen > metal oxide
Reaction with water
Alkali metals
Produce alkalis and hydrogen gas
Group 1 metal + water > group 1 metal hydroxide + hydrogen
Reaction with acid
Hydrogen is produced
Metal + acid > ionic salt + hydrogen
Extraction of metals
Depends on reactivity
Unreactive are found in their natural state
Less reactive you heat the metal ore in the air
Reactive you heat the metal ore with carbon
More reactive you use electrolysis of molten compound, using electricity to cause a chemical reaction
Metallic nanomaterials
The high surface area to volume ratio increases reactivity and catalytic potential
Have different physical and chemical properties but have the same metallic structure
