Chemistry C2.2 : Structure and properties

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  • Created by: TillyF
  • Created on: 20-12-16 06:41
What holds an ions in a giant ionic lattice together?
The attractive electrostatic forces between the oppositely charged ions act in all directions and are very strong, holding the ions in the lattice together tightly.
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What causes the ionic bonds?
The strong electrostatic forces of attraction between the oppositely charged ions.
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Why do ionic compounds have high melting and boiling points?
It takes a lot of energy to break up a giant ionic lattice, there are a lot of ionic bonds to break. To separate the ions we have to overcome all those electrostatic forces of attraction, hence the high melting and boiling points.
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Why can't a solid ionic compound conduct electricity?
The ions in a solid ionic compound are held in a fixed position in the lattice, so they cannot move around and can only vibrate on the spot when solid.
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What happens when the ionic solid melts and becomes a liquid?
The ions are free to move anywhere in the liquid and can carry their electrical charge through the molten liquid and therefore can conduct electricity.
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What happens when ionic compounds dissolve in water and become a solution?
When an ionic compound dissolves in water, the lattice splits up by the water molecules. So, the ions are free to move around the solution, and the solution can then conduct electricity.
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Describe the structure of the ions in an ionic solid?
Ions are fixed in a lattice, they vibrate but cannot move around and do not conduct electricity.
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Describe the structure of the ions in a molten ionic compound?
High temperature provides enough energy to overcome the strong electrostatic force between the ions. They are then free to move within the molten compound and so can conduct electricity.
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Describe the structure of the ions in a ionic compound solution?
Water molecules separate ions from the lattice. The ions are free to move around within the solution, so it does conduct electricity.
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Why are covalently bonded molecules liquids or gases at room temperature?
They have low melting and boiling points.
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Why do covalently bonded molecules have low melting/boiling points?
The molecules are quite separate from each other and the attraction between the individual molecules in a covalent substance are small. They have weak intermolecular forces between molecules, so little energy is needed to overcome these forces.
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Describe the strength of the bonds and intermolecular forces between covalently bonded substances?
The intermolecular forces between the bonds are weak but the covalent bonds between each atom are very strong.
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What is overcome in order to melt the covalently bonded substance?
The weak intermolecular forces are overcome to melt the covalently bonded substance, the bonds between the atoms remain strong and are not broken when melted.
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Why will a substance made up of simple molecules not conduct electricity, even though it is a liquid at room temperature?
There is no overall charge on the simple molecules in a compound , making it impossible for substance made up of simple molecules to conduct electricity.
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What are giant covalent bonds?
A huge network of atoms held together by covalent bonds, they are sometimes called macromolecules.
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Give three examples of giant covalent structures?
Diamond, graphite and silicon dioxide have giant covalent structures.
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What are some properties of giant covalent structures and why?
All atoms in these giant lattices are held in position by strong covalent bonds, they are very hard, have high melting/boiling points and are insoluble in water.
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Why is diamond so hard?
Diamond is so hard as all of its carbon atoms each form four strong covalent bonds.
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Why can the layers in graphite slide?
In graphite, carbon atoms are only bonded to three other carbon atoms. They form hexagons arranged in giant layers, there are no covalent bonds between the layers, so the layers can slide over one another easily. Hence why graphite is a soft material
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Why can graphite conduct electricity?
Carbon atoms in graphite layers form 3 strong covalent bonds, carbon has 4 electrons in its outer shell available for bonding, so there is one free electron. This electron is a delocalised electron and can move between layers, allowing conductivity.
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What are the free electrons in graphite called?
Delocalised electrons
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Describe the structure of graphite?
Weak intermolecular forces between layers in graphite, can slide over one another. The carbon atoms are arranged in hexagons, with 3 covalent bonds, leaving 1 free electron on each carbon atom (carbon has 4 electrons in outer shell) (delocalised)
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What is fullereness?
Large carbon molecules containing cage like structures
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What can we potentially use these fullerenes molecules for?
Scientists can now place other molecules inside these carbon cages, scientists could deliver drugs to specific parts of the body through the use of fullerenes and they could be used for nanoscience applications, eg. for catalysts and lubricants
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Why can we bend pure metals into different shapes?
The layers of atoms in a pure metal are able to slide easily over each other.
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Why can the atoms in a giant metallic structure slide over one another?
The atoms in a pure metal are held together in giant metallic structures, the atoms are arranged in closely-packed layers. Due to the regular arrangement, the atoms can slide over one another easily, hence why pure metals are soft.
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What is an alloy?
An alloy is a mixture of metals.
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Describe the structure of an alloy and why they are harder than pure metals?
In an alloy a non-metal and a metal are usually mixed eg. steel is made from iron and carbon. So the atoms in the alloy are different sizes, making it difficult for the layers in the metal's giant structure to slide over each other, alloys are harder
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How are positive ions held together in a metal's structure?
The positive ions in a metal's giant structure are held together by a sea of delocalised electrons. These electrons are a bit like 'glue'. Their negative charge between the positively charged ions holds the ions in position.
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How come a metal lattice is able to distort?
The electrons can move through the whole giant lattice, they can move around and hold metal ions together at the same time, the delocalised electrons enable the lattice to distort.When struck,metal atoms can slip past one and not break structure
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Why are metals good conductors of heat and electricity?
The delocalised electrons can flow through the giant metallic lattice, the electrical current and heat are transferred quickly through the metal by the free electrons.
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What is a shape memory alloy?
A shape memory alloy is a metal that can be deformed into different shapes and when heated can return to its original shape.
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What can we use shape memory alloys for?
Doctors treating a badly broken bone can use allots to hold the bones in place while they heal, they cool the alloy before it is wrapped, when it heats up again the alloy goes back to its original shape and pulls the bones together while they heal.
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How can we make a polymer?
We can make polymers from chemicals made from crude oil, small molecules called monomers join together to make bigger molecules called polymers. As monomers join together they produce long chained molecules eg. poly(ethene)
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What do the properties of polymers depend on?
-the monomers used to make it -the conditions we choose to carry out the reaction
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What are the two different reaction conditions for making polymers?
Low density polymers: high pressure and a trace of oxygen High density: using a catalyst at 50 degrees C and a slightly raised pressure
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What are the polymer chains like in low density polymers?
The polymer chains are branched and cant pack closely together
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What are the polymer chains like in high density polymers?
The polymer molecules are straighter and can pack more closely together than branched chains, they have higher softening temperatures and are stronger than low density polymers.
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What is a thermo softening polymer?
A polymer that can soften easily, that will reset when they cool down, they are made up of individual polymer chains that are tangles together.
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What is a thermo setting polymer?
Thermo setting polymers do not melt when we heat them, they have strong covalent bonds forming cross links between their polymer chains.
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Why can thermo softening polymers be remoulded?
Forces between the polymer chains are weak, when heated the weak intermolecular forces break and the polymer becomes soft. When it cooled, the intermolecular forces bring the polymer molecules back together and the polymer hardens again
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Describe how thermo setting polymers structure make their covalent bonds strong?
Their monomers make covalent bonds between the polymer chains when heated to shape them, the covalent bonds are strong and stop the polymer from softening. The cross links between the chains stop separation, even if heated strongly they dont soften
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What happens to thermo setting polymers when heated strongly?
They never soften due to the covalent cross links in between the polymer chains, the polymer will char at high enough temperatures.
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What is nano science?
Nano science is the science of very small particles that are between 1 and 100 nanometers in size
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What is a property of a nano particle?
A nano particle has a huge surface area for a small volume of material.
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How can nano science be used for glass coating?
Glass can be coated with titanium oxide nanoparticles, sunshine triggers a chemical reaction, breaking down dirt which lands on the window and when it rains, the water spreads evenly over the surface of the glass, washing off the broken dirt.
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How can nano particles be used in sun tan lotion?
Titanium oxide and zinc oxide nanoparticles are used in sunscreen. Nanoparticles of a metal oxide with a coating of silica, that can be adjusted. Te coated nanoparticles are effective at blocking the sun rays more than UV absorbers.
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How can nanoparticles be used in the cosmetic industry?
Nanoparticles in face creams are more effective at being absorbed deeper into the skin, they are used in sun tan creams and deodorants.
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How are nanoparticles being applied to medicines?
The nano cages of gold can be used to deliver drugs where they need to go in the body, they can be absorbed by tumours, where the vessels with holes large enough for the gold to pass into. A laser directed to nanoparticles can destroy tumour cells
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How can nanoparticles be used to transfer drugs?
Gold nano cages could carry cancer-fighting drugs to a tumour and carbon nano cages could be used to deliver drugs to the body
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What could silver nano particles do?
Silver nano particles are antibacterial, they act against viruses and fungi and can be used in sprays to clean operating theatres in hospitals.
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Future developments with nano particles?
Nano tubes can be made into nano wires, to make small electronic circuits. Nano tube sensors could detect potential asthma attacks, they could improve the memory capacities and speeds of computers. Nanotech suits to protect army from bullets
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Possible risks of nano particles?
The large surface area of nano particles could make them effective as catalysts but could cause of violent explosion if a spark is made. Breathing in tiny particles could damage lungs or enter the blood stream and cause unpredictable effects.
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