Natural and Synthetic materials
CHEMICAL: AN ATOM/ A GROUP OF ATOMS BONDED TOGETHER
Some materials occur naturally from plants (wood, paper, cotton) + animals (wool, silk, leather)
- Rubber used to come from the rubber tree, now we also make it in a factory, advantage= comtrol its properities
- Lots of clothes made of man-made materials like nylon or polyester- properties can be controlled
- most paints are made of man-made chemicals. The pigment and the stuff that holds it together are tought to stop it fading.
Raw materials used to make synthetic materials come from the Earth's crust.
Materials and Properties
DIFFERENT MATERIALS HAVE DIFFERENT PROPERTIES
- MELTING POINT
- STRENGTH- how good it is at resisting a force- two types= TENSILE (how much a material can resist a pulling force) and COMPRESSIVE (how much it can resist a pushing force)
- STIFFNESS- how good it is at not bending when a force is applied to it.
- HARDNESS- how difficult it is to cut into
- DENSITY- material's mass per unit volume (g/cm3)
Materials, properties and uses
Possible uses depend on properties:
- Plastics: can be fairly hard, strong and stiff, some low density, some mouldable.
- Rubber: strong but soft and flexible, mouldable
- Nylon fibres- soft and flexible, good tensile strength
Products properties depend on what it is made from, materials affcet the effectiveness and durability
- Effectiveness= how good it is at it's job
In exam, may need to access the suitability of different materials for products e.g.
- Cooking utensils= high melting point, a non-toxic one
- Toy car= non-toxic, strong, stuff and low density
- Clothing fabric= not stiff, good tensile strength, high-flame resistance.
Crude oil- mixture of hydrocarbons
Hydrocarbon properties change as the chain gets longer
- Short chain= lower boiling points, often gases
- Long chain= higher boiling points, often quite viscous
- Two types of bond= strong covalent bond (between carbons and hydrogens within each molecule) Intermolecular forces of attraction (between different hydrocarbon molecules)
- Crude oil heated= molecules supplied with extra energy- makes molecules move more and may eventually overcome intermolecular forces and turn into a gas.
- Covalent bonds are much stronger than the intermolecular forces, so they don't break.
- Intermolecular forces break a lot more easily in small molecules because the bonds are stronger in longer molecules- loads of other places where the bonds are- that's why bigger molecules have higher boiling points
Uses of crude oil
Separated by fractional distilliation (refining)
- Separated into groups with similar boiling points
- each group- a fraction
- uses depend on its length
- crude oil has various uses
- petrochemical industry- refines crude oil to produce fuels and lubricants, also produces raw materials that can be used to make syntheic chemicals
- most hydrocarbons are used to produce fuels
- a small amount of hydrocarbons from crude oil are used to make new compounds for use in things like plastic, medicines, fertilisers and sometimes food
- somes of the less useful hydrocarbons can be split apart to make more useful hydrocarbons and ethene
CHEMICAL SYNTHESIS= process of making new compounds
Polymerisation- lots of small molecules link
- Plastics form when lots of monomers join together to make a monomer- usually carbon based- under high pressure many small molecules polymerise to form long chains (polymers)
- strong and rigid polymers- high-density polyethene (e.g milk bottles)
- light, stretchable polymers- low-density polyethene for plastic bags and squeezy bottles- low density polyethene has a low melting point
- PVC- strong and durable, can either be rigid or stretchy, used to make window frames and piping- stretchy= synthetic leather
- Polystyrene foam- used in packaging, good insulator
- Heat resistant polymers- used got kettles
Polymers have replaced synthetic materials- nylon and polyester used to replace cotton, wool, silk bc lighter, durable, water resistant, cheaper- but aren't breathable. Rigid PVC- largely replaced wood as new material for window frames, weather-resistant, durable, strong, security better, easier to maintain.
Structure and Properties of polymers
Properties depend on how they are held together and how the molecules are arranged
- Packed close together= high density
- Weak forces= tend to slide over eachother, stretched easily, low melting point
- Strong forces= higher melting point, not easily stretched, croos-links holf firmly together. Crosslinks are chemical bonds between polymer chains.
Polymers can be modified to gove them different properties..
- increase chain length- shorter=easier to shape and lower melting points
- increase strength by adding cross-linking agents, these chemically bond chains together making them stiffer, stronger and more heat resistant.
- Plasticisers can be added to make is softer and easier to shape, work by getting inbetween polymer chains and reducing the forces between them.
- Polymer can be made more crystalline. A crystalline polymer has straight chains with no branches so they can fit close together, they have a high density, stronger and have a higher melting point.
Nanotechnology=working w. really tiny particles
- Often designed for a specific use
- Occur naturally in nature= seaspray (salt) and combustion (soot)
- can be used to modify properties of sports equipment (stronger and more durable but don't add weight)
- Medical equipment- silver nanoparticles added to bandages and surgical masks because it gives them antibacterial properties.
- Nanoparticles are much smaller than particles of the same material, meaning they have a larger surface area to volume ratio, which gives them different properties and makes them useful. Silver nanoparticles can kill bacteria, making them suitable for wound dressings.
- Effects on health not fully understood, important tests are done to minimize the risks. Some people are concerned about the long term impacts on health and as long as it's unknown people believe products containing nanoparticles should be labelled.