Bonding Flashcards
When does ionic bonding happen?
When a metal reacts with a non metal - oppositely charges particles
What is ionic bonding?
When the electron is transferred
What is the compound between a metal and non metal called?
An ionic compound
What are the properties of metals?
- They conduct electricity
- They conduct heat
- They are malleable and ductile
- They have high melting and boiling points
What energy keeps ionic bonds together?
Electrostatic force of attraction
What is covalent bonding?
Sharing electrons
Are covalent or ionic bonds stronger?
Ionic
What does covalent bonding involve?
Two non metals
Do covalent bonds have high or low melting points?
Low
How are metals structured?
A lattice of atoms and a sea of free electrons
What do thermochromic things control?
Temperature
What do photochromic things change?
Light
What can hydrogels do?
Absorb water
How big are nano particles?
1x10(-9)m
What properties does silver/silver nitrate have?
Antibacterial properties
How reactive are alkanes?
Not at all
What are the properties of an ionic compound?
- A three dimensional lattice structure (giant ionic structure)
- A high melting point
- They conduct electricity when molten or dissolved in water
- They’re brittle
How are ions in a sodium chloride crystal arranged?
In a cubic lattice - each ion is surrounded by six nearest neighbors of opposite charge
What kind of compound is water?
A covalent compound
Do covalent bonds conduct electricity?
Nein
How strong is the energy within a covalent bond?
Within the bond it is very strong but the molecules attract each other weakly, so they have low boiling points
What melting points do giant covalent compounds have?
High ones as atoms are held together by very strong covalent bonds
Give two examples of giant covalent structures
Diamond and graphite
What are diamond and graphite made out of?
Carbón
What are carbon atoms in diamond connected to?
Four other carbon atoms, meaning that it’s a three dimensional lattice based on a tetrahedral unit cell
What is graphite made of?
Layers of carbon atoms in hexagonal rings - bind between layers are quite weak and allow layers to slide over one and other
What are the properties of diamonds?
Transparent, an electrical insulator, very high melting point (3500 degrees) very hard
What are the qualities of graphite?
Grey/black shiny solid, very soft (lubricant) also pencils, conducts electricity, high melting point (3600)
Can graphite cells conduct electricity across layers?
No
What are fullerenes?
Allotropes of carbon made up of balls or tubes or carbon atoms
What are the properties of carbon nanotubes?
They’re very stiff and strong and have higher electrical conductivity than copper - and in a tube 10000 times thinner than a human hair
How are carbon nanotubes formed?
When graphite layers form and then roll up into tubes rather than being deposited in layers
What melting point do carbon nanotubes have?
A very high one
How conductive are carbon nanotubes?
Very
What are buckyballs?
A giant molecule of 60 carbon atoms in the shape of a ball
What do buckyballs fit together to form?
A transparent yellow solid called fullerite
What properties do buckyballs have?
Similar ones to nanotubes
What is an advantage of buckyballs compared to nanotubes?
They can trap other molecules and therefore carry drugs to specific sites in the body
What is graphene?
One layer of a graphite molecule
What are the qualities of graphene?
- The thinnest material known to man
- The lightest material known to man
- 100-300 times stronger than steel
- The best conductor of heat at room temperature and the best conductor of electricity known
Why are nano particles more useful than normal particles?
Because they have a much larger surface area for their size than other particles
Why is the size of a silver nano particle particularly useful?
Because it can enter a living cell
Why are some people anxious about nano particles?
Because some people don’t know their long term effects
What is titanium dioxide?
A white solid used in house paint and coating some chocolates
How small are titanium nano-particles
So small that they are invisible
Why is titanium dioxide used in sun-cream?
Because it’s invisible but can block harmful ultraviolet light
What do we have to do to titanium dioxide in suncream?
Coat it in something so it isn’t absorbed into the skin
Is titanium dioxide harmful?
Not obviously, but some people think we don’t know enough yet
Define smart materials
Materials with properties that change reversibly with a change in their surroundings
What are most thermometric materials based on?
Liquid crystal technology
What is liquid crystal technology also used in?
Flat screen televisions
How do liquid crystals work?
At a specific temperature they re-orientate to produce a change in colour and then go back when the temperature changes
What are thermochromic pigments used in?
Mugs than change colour with heat etc.
What do photochromic pigments contain?
Special organic molecules that change colour when exposed to light or ultraviolet light
What does light do to photochromic pigments?
It breaks a bond in the molecules, which then rearranges itself. It can return to its original form after
What are photochromic pigments used in?
Photochromic lenses in glasses which allow normal glasses to become sunglasses
What are shape-memory polymers?
Plastics which can regain their shape when they’re heated and then re-cooled
What is the property in shape-memory molecules called?
Shape retention
What are shape memory polymers used for in industry?
In the building industry for window frame sealing and manufacturing gum shields
What are the future applications of shape-memory polymers
Plastic car bodies from which a dent could be removed by heating
What’s the difference between a shape-memory polymer and shape-memory alloy?
The polymer is made of plastic and alloy of metal
What are the remarkable properties of some shape-memory alloys (nickel/titanium alloys, known as NiTi)
- Pseudo elasticity (they appear to be plastic)
- Shape retention
What are the possible uses of shape-memory alloys?
Deformable spectacle frames, and surgical plates for joining bone fractures
What are hydrogels?
Polymer gels that absorb or expel water and swell and shrink up to 1000 times their volume due to changes in pH or temperature
How are hydrogels structured?
They are cross-linked to polymers that enable water and some other liquids to be absorbed within the structure, making it swell
What do the applications of hydrogels (polymer gels) include?
Artificial muscles, granules added to house plant compost to retain water, filling for nappies
