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Chemistry: CGSE WJEC Structural bonding 2.1
Terms in this set (55)
Structure of metals?
Sea of electrons.
Held together by atraction between electrons and ions called metallic bonds
Positive ion amount changes along with free electrons in accordance with ....
Amount of electrons in outer shell.
Metal high melting and boiling point?
Lots of heat energy to break up lattice because of strong metallic bonds.
As melting point increases the number of ....
Outer shell electrons increases.
Higher the charge on metal ion the greater the force of attraction between 'it' and sea of delocalised electrons.
Metals malleable and ductile?
Layers can slide over each other without metallic bond breaking as electrons free to move.
Metals good conductors of heat?
Free electrons absorb heat which makes them move faster. They transfer heat enfers through structure quickly.
Metals good conductors electricity?
Free electrons move through electron carrying charge when voltage applied across structure.
IONIC COMPOUND high melting and boiling points?
Bigger the charge, stronger the electrostatic force. Ionic bonds VERY strong, LOTS of heat energy to break up lattice.
Higher charged ions are...
More reactive, they have greater attractive forces, higher melting and boiling points.
Weak forces easier to change state.
IONIC COMPOUND soluble in water?
Water molecules attract IONS AWAY from lattice. Ions move freely surround by water molecules.
Ionic compounds conduct electricity when melted or dissolved
SOLID IONIC COMPOUNDS DON'T CONDUCT ELECTRICITY.
BUT, WHEN LATTICE MELTED/ broken up they are FREE to move. As they are charged THEY CAN CONDUCT ELECTRICITY.
Simple molecular solids low melting and boiling?
Forces between molecules weak.
Simple molecular doesn't conduct electricity?
NOT CHARGED SO CANNOT.
What don't most simple molecular substances do?
Dissolve in water.
Giant molecular substances high melting and boiling points?
STRONG BONDS aren't easily broken. Each atom held by strong covalent bonds.
What don't giant molecular substances do?
Conduct electricity, dissolve in water.
-Drill bits, cutting and drilling rock
Diamond and graphite are ...
Giant covalent structures
Carbons forms covalent bonds to 4 others, each outer atom bonds to 3 more e.c.t
Grey/black, shiny, solid, very soft.
Each carbons atom forms covalent bonds to 3 others which gives rings of 6 atoms.
- very hard
- very high melting and boiling point
-can't conduct electricity
Why diamonds very hard?
Each atoms held by 4 STRONG COVALENT BONDS.
Diamond Very high melting and boiling point?
It is bonded to 4 strong covalent bonds, the force is strong therefore it takes a lot of heat energy to overcome.
Diamond can't conduct electricity?
No free electrons or ions to carry charge.
- soft and slippery
- good conductors of electricity
-high melting and boiling point
Graphite soft and slippery?
Sheets slide over each other therefore good for pencils as easily put onto page.
Graphite good conductors of electricity?
Each atom has 4 outer electrons but only forms 3 bonds therefore the 4th electron can carry charge throughout structure.
Graphite High melting and boiling point?
Bonded by 3 strong covalent bonds, high force of attraction hard to overcome takes a lot of energy.
Graphene is ...
A Single layer of carbon atoms bonded in hexagonal lattice
Graphene properties (5)
-thinnest material (1 atom thick)
-100 to 399 time stronger than steel
-best conductor of heat at room temp
-best conductor of electricity known
Graphene potential uses? (4)
-touch panels (smart screens)
-desalination of sea water.
Graphene commercially available?
Charged structures made entirely of carbon atoms e.g Buckminster fullerene c
What are Carbon nanotubes?
Roles of carbon hexagons similar to graphite
carbon nanotubes properties (4)
-V small diameter (10,000 times less than human hair)
- v low density
- extremely strong
Why carbon nanotubes strong?
Each C atom is covalently bonded to 3 others. Covalent bonds v strong.
Why carbon nanotubes great conductor of electricity?
Each C atom has 3 covalent bonds. 4th bonding electron Free to move through layer carrying charge.
Carbon nanotubes uses?
-connections inside miniature electronic circuits
-can also behave as semi conductor like silicon.
Elements react to become ...
Inert or stable
Elements become inert or stable by ...
Transferring or sharing electrons
Why do electrons transfer or share electrons?
To gain full outer shell.
Ionic (electrovalent) bonding?
Metal transfers electrons to non-metal.
Lose them +
Gain them -
Covalent bonds are ...
2 or more non-metals sharing electrons
1 shared pair •~ represented by -
2 shared pairs •~•~ represented by -
3 shared pairs •~•~•~ represented by -
Nanoscale particles are ... (size)
1-100 nanometers (nm)
Nano-scale particles have .........
Different properties from their bulk material because they have a very large surface area.
Nanoscale particles are?
Easily absorbed through the skin.
There haven't been ...... ....... to know the ....... .......
Enough studies. Adverse effects.
May be harmful.
Silver has ............ effects
Antibacterial effects, they're used in linings of fridges and plasters.
SMART materials definition
Materials with properties that change reversibly in response to change in surroundings.
When heating the polymer softens, on cooling it remains in the deformed state. On being reheated, It 'remembers' original shape.
E.g gum shields, medical structures
Thermochromic paints and colourents
Changes colour over a specified temp range
E.g t-shirts that change colour at body temp, coffee mugs
Photochromic paints and colourants.
When exposed to light, changes colour. It rearranged itself into molecule with different colour. When light source removed, molecule returns to it's original form.
E.g sunglasses lenses, windows.
Pseudo-elasticity and shape-retention memory.
Appear to be elastic and when deformed they return to original shape after heating.
E.g deformable spectacle frames, surgical plates for joining bone fractures, surgical surds that replace tendons.
They have the ability to absorb or expel water when subjected to temp change, exposure to infra-red light or change in pH
Possible application = artificial muscles , underground water cut-off in oil industry.
Hydrogels are also more effective than fire-fighting foam.
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