C3 Structure and Bonding Flashcards
What are the different methods of changing state?
Freezing - liquid to solid
Melting - solid to liquid
Condensing - gas to liquid
Boiling - liquid to gas
Sublimation - solid to gas
Deposition - gas to solid
What happens when a substance condenses?
- Thermal energy is lost
- Particles move slower and closer together
- Some forces are stronger, some particles touch because of the stronger force of attraction
What happens when a substance melts?
- Particles gain thermal energy + move more
- Some forces between particles are overcome
- Particles move other each other
What happens when a substance boils?
- Particles gain more energy and move more
- Remaining forces between particles are overcome
- Particles move far apart
How do particles move as a solid, liquid and gas?
Solid - vibrate at a fixed point
Liquid - vibrate and move in a fixed volume
Gas - vibrate and move rapidly in random directions.
What are the formulas and charges of the polyatomic ions?
- OH - hydroxide (-)
- CO3 - carbonate (2-)
- NO3 - nitrate (-)
- SO4 - sulfate (2-)
- NH4 - ammonium (+)
- H - hydrogen (+)
How do you work out the formulae of ionic compounds?
Ionic compounds contain positive and negative ions which form an overall neutral particle. There must be an equal amount of positive and negative charges in the compund meaning there are more of some ions than others in sone ionic compounds, e.g lithium oxide is Li2O.
What is ionic bonding?
The strong electrostatic force of attraction between oppositely charged metal and non-metal ions.
What are cations and anions?
cations - positively charged ions
anions - negatively charged ions
How do you draw ionic bond diagrams?
You draw ions of the equivalent amount to the number of ions in the formula. e.g for MgF2 you draw one magnesium ion and 2 fluoride ions together, remembering to label charges and use square brackets.
What is the structure of any ionic compound?
A giant ionic lattice - large numbers of ions are regularly arranged in a repeating pattern.
What is the melting point of giant ionic lattices? Why?
The melting point is very high because of the large amounts of energy needed to overcome the many strong electrostatic forces of attraction throughout the salt crystal.
Mention
* Strength (+ number) of bonds or forces
* Amount of energy required to overcome bonds or forces
* Therefore, high or low melting point
Do giant ionic lattices conduct electricity?
Ionic compounds can only conduct when molten (liquid) or dissolved in solution, as ions are free to move and carry a charge throughout the circuit/material.
What is metallic bonding?
The strong electrostatic attraction between positive metal ions and negative delocalised electrons.
What is the structure of giant metallic structures?
Giant metallic structures are formed of regular layers of positive metal ions surrounded by a sea of delocalised electrons. You draw this by as a diagram by drawing rows of circles (+ metal ions) with a plus inside surrounded by minuses (electrons) to represent the + ions surrounded by delocalised electrons.
Do giant metallic structures have a high or low melting point? Why?
High melting point as a lot of energy is required to overcome the strong electrostatic forces of attraction between + ions and - delocalised electrons.
Do giant metallic structure conduct?
Yes, delocalised electrons carry electrical charge and thermal energy through the metal.
Are pure metals ductile and malleable?
Ductile and malleable because:
* arranged in layers/rows
* atoms/ions are the same size
* layers can slide over each other easily when a force is applied
Why are alloys stronger and harder the pure metals?
There are different sized atoms so the layers cannot slide past each other as easily.
How is a covalent bond formed?
When 2 atoms share a pair of electrons
How do you draw dot and cross diagrams for covalent bonds?
Draw outer shell electron structures for each atom overlapping with shared electrons in the overlap (one atom crosses, other dots)
What are small/simple molecules?
Contain only a few atoms held together by covalent bond.
Why is carbon dioxide a gas at room temperature?
- Simple molecules
- Have weak intermolecular forces
- Little energy is needed to overcome these weak forces
- so CO2 boils at very low temperatures
Do simple molecules conduct?
Do not conduct electricity because there are no charged particles - only neutral molecules
Why do boiling points increase down group 7?
- molecules become larger
- stronger/more intermolecular forces between larger molecules
- so more energy needed to overcome the intermolecular forces.
What are some disadvantages of different molecules diagrams?
- 2D ball and stick model shows which atoms bonded to each other, but not true shape of the molecule. 3D attempts to show this.
- Dot & Cross diagrams show which atom electrons in bonds came from originally, but in reality all electrons are identical.
- On all models drawn on paper, the electrons are in fixed positions between 2 atoms, scientists believe electrons in covalent bonds are constantly moving.
- In giant structures, models can never accurately reflect millions of atoms/ions bonded together in giant structure.
What are polymers made up of?
Many small reactive molecules that bond to each other to form long chains.
What is the simplest example of a polymer? How do we represent it?
Poly(ethene) which is made up from thousands of small ethene molecules, C2H4, reacting together.
We can represent long polymer chains in poly(ethene) like this:
H H H H H H
| | | | | |
-C-C-C- C- C -C- etc.
| | | | | |
H H H H H H
Instead of showing all covalent bonds, this can be abbreviated by using the repeating unit of the polymer chain where a portion of the molecule (C2H4) is placed in brackets with an ‘n’ at the bottom right outside brackets (1/3 of molecule above).
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What are 3 giant covalent structures?
Diamond
Graphite
Silicon dioxide
What is the bonding and structure of diamond?
Bonding
* Each carbon atom covalently bonded to 4 others.
* Strong covalent bonds
* No free electrons
Structure
* Giant Covalent Lattice
* 3D rigid tetrahedral structure
* No layers
What is the bonding and structure of graphite?
Bonding
* Each carbon atom covalently bonded to 3 others.
* Strong covalent bonds
*Delocalised electrons
Structure
* Giant covalent structure of layers of hexagonal rings
* Weak intermolecular forces between the layers that can slide
What are some properties of diamond and why?
- Very hard and strong - rigid tetrahedron structure
- High melting and point - strong covalent bonds take a lot of energy to overcome
- Poor conductor - no delocalised electrons
- Used as cutting tools
Silicon dioxide (sand) has a very similar structure and properties to diamond
What are some properties of graphite and why?
- Soft and slippery - layers can slide over each other easily
- High melting and point - strong covalent bonds take a lot of energy to overcome
- Good conductor - delocalised electrons can carry charge through the structure
- Used as lubricants and pencils
What are fullerenes?
The general name for all hollow-shaped alletropes of carbon.
What is buckminster fullerene and what is its structure?
Buckminster fullerene, C60, is a spherical carbon alletrope where 60 carbon atoms are assembled in pentagons and hexagons, in a geometry similar to a football.
* Made up of 20x hexagons + 12x pentagons
* Strong covalent bonds
* Simple molecule
What are some properties of buckminster fullerene and why?
- Low melting point - weak intermolecular forces between molecules need little energy to overcome
- Bad conductor - although delocalised electrons can move through the molecule, they cannot jump between molecules.
- High tensile strength - cage-like structure makes them very stable
What are uses of buckminster fullerenes? why?
Lubricants - molecules are spherical so will roll.
What are carbon nanotubes and what is its structure?
Carbon nanotubes are fullerenes that have a cylindrical structure made of a layer of carbon atoms bonded together in a hexagonal (honeycomb) mesh.
What are some properties of carbon nanotubes?
- Very high melting point - each carbon atom joined to 3 others by strong covalent bonds
- Good condutors - spare electrons which form a sea of delocalised electrons within the tube.
- Very strong - very strong covalent bonds within molecule
- Low density
What is a use of carbon nanotubes? why?
Electronics - very strong and are good conductors
What could fullerenes be used for? why?
Drug delivery into the body - cage-like structures could be used as ‘bucky-mules’ to deliver drugs or radiactive atoms to treat cancer at very specific sites within the body. Fullerenes are more easily absorbed than other particles making them more effective for targeting specific areas where drugs are needed.
What is graphene and what is its structure?
Graphene is a single layer of carbon atoms tightly bound in a hexagonal (honeycomb) lattice with strong covalent bonds.
What are some properties of graphene?
- Very good conductor (better that graphite) - delocalised electrons can move through the material
- Low density
- Most reactive form of carbon
- Very strong (200x stronger than steel, strongest material ever found) - simple structure with very strong covalent bonds
- Very high melting point - strong covalent bonds
- Very light and flexible - single layer of atoms
What is a use of graphene?
Flexible electronics - single layer of atoms so flexible, good conductor, strong, light
What are nanoparticles?
Tiny particles made up of a few hundred atoms, which are 1-100nm.
What is the use of nanoparticles called?
Nanoscience
How big are fine and coarse particles?
Fine particles - 100 - 2500nm PM2.5
Coarse particles/dust - 2500nm - 10000nm PM10
How do catalysts increase the speed of reactions?
By providing an alternate reaction pathway that has a lower activation energy.
How could nanoparticles improve catalysts? What is the risk?
Their high surface area to volume ratio could help to improve catalysts.
However, it also makes them dangerous. If a spark is made by an accident near a large quantity of the catalyst, there could be a violent explosion.
What are 2 ways to increase the surface area to volume ratio of an object?
- bumpier surface
- be smaller - as particles decrease in size the size of the surface area increases relative to the volume.
How do you work at the simplest SA:V ratio?
SA = width x length x faces
V = base x height x depth
Divide both values by the smallest value to get the simplest SA:V ratio
What is the typical diameter of an individual atom?
0.1nm
How can nanoparticles be used in sunscreen? What are the negatives?
Titanium dioxide in nanoparticle form can be used in sunscreen as it blocks UV light and leaves no white marks on the skin. It also provides better coverage than other sunscreens.
However, it may be difficult to see where sunscreen is applied as it is invisible and nanoparticles may be toxic to some cells - testing has not yet been done.
How are silver nanoparticles used? What is the problem?
Silver nanoparticles have antibacterial properties (kill bacteria).
This means it can be incorporated into surgical masks, plasters and wound dressings in medicine as well as in deodorant and clothes as incorporated deodorant to reduce smells by killing the bacteria.
However if the silver nanoparticles escape it may get into rivers and kill or harm fish and other marine life, or kill useful bacteria in the environment.
