2.3 Metallic Bonding and 2.4 Models to Materials

What is metallic bonding?

Electrostatic attraction between delocalised free moving electrons and the positively charged metal ions.

Characteristics of a metal?

• low relative electronegativity

• great conductor of heat and electricity

• lustrous

• sonorous

• high MP BP

• malleable + ductile

• tends to corrode

Why is metal malleable?

• metallic bonds are non directional (uniform charge across the structure as electrons as electrons are shared across multiple atoms in all directions)

• this allows layers of cations to slide past each other rearranging the shape of the lattice

• without breaking the electrostatic attaction

Why can Metals conduct heat?

• when metals are heated, the the cations in the metal lattice vibrate more vigotously

• these vibrating cationns transfer their kinetic energy as they collide with neighbouring cations

• the cations vibrate and transfer the heat to the delocalised electrons that can move and tranfer the heat rapidly throughout the metal

What determines rge strength of a metallic bond?

• the greater the charge on the metal ion, the more delocalised electrons + higher charge difference

• strong electrostatic attraction

Trend in Period 3 metals

• MP increases from left to right

• as their is a decrease in ionic radius

• increase in ionic charge

• and increased electron density

Transition metals:

• metals that partially fill the D orbital as an atom or an ion

• exception: Cu : [Ar] 4s1 3d10

why do transition metals have a higher melting point than group 1 and 2?

• the electrons in the D sublevel become delocalised as well as the electrons of the outer level

• increased electron density means stronger electrostatic forces of attraction (cations + electrons)

• lots of heat energy to break attraction

What is elastic mtaerial?

materials that will change hspae when subjected to a force and return to thier original shape after the force is removed

What is a plastic material?

A material that changes and retains its deformed shape evn after the extrenal force is removed

Semiconductor:

A poor electrical conductor but bettwe when heated, illuminated or impure

Alloys:

• when a pure metallic element is mixed with other metalic or non-metallic elements (mixtures)

• ions of diff elemts are bound togetehr by delocalised electrons

Why are alloys stronger than pure metals?

• alloys have a non-uniform packing of cations in the lattice

• atoms of different sizes which distort/disrupt the regular arrangement of cations

• this makes it more difficult for the layers to slide over eachother

Name 4 examples of alloys?

Brass, Steel, Stainless Steel and Bronze

Brass:

• copper and zinc

• strong + resistant to corrosion

• door hing

Stainless Steel:

• Iron, Chromium, nickel, carbon

• corrosion resistant

• cutlery, surgical instruments

Bronze:

• copper and tin

• hard + strong, resistance to corrosion

• medals, sculptures, ship fittings

Polymer:

Covalently bonded macromolecules characterised by low thermal and eletcrical conductivity

Examples of Natural polymers:

• cellulose

• DNA

• Starch

Examples of synthetic polymers:

• polyester

• nylon

• teflon

Properties of Plastic:

• low weight: polymers are loosley packed so will be less dense

• unreactive: additon polymers from alkenes are saturated- no more bonds left

• water resistant: hydrocarbon chains are hydrophobic

• strong: lots of covalent bonds

Ethene into Polyethene:

Chloroethen into Polychloroethene:

Propene into Polypropene:

Diacid + Diamine →

Polyamide

To form a polymer a molecule must have atleast:

2 reactive functional groups or else an esther is formed

Coordination Bond:

when both the electrosn from the pair are from the same atom

benefits and engatives of bioplastics:

+ves: can be degraded quickly without releasing CO2 so don’t pollute the planet + can be made from renewable feed stocks

-ves: can be broken down quicky so may not functional in the longterm + it can cause eutrophicatiob