C2 Flashcards
What are the two phases in chromatography?
`A stationary phase that does not move. A mobile phase that does move
What is the stationary phase in paper chromatography?
The absorbent paper
What is the stationary phase of gas chromatography?
Silica or alumina powder packed into a metal column
Why can carbon form many different compounds?
It has 4 valence electrons and can form 4 covalent bonds. It can join with other carbon atoms to form chains and rings or form covalent bonds with other elements
Why are diamond and graphite different?
Because they have different structure and bonding
What is a nanotube?
A sheet of graphene rolled into a tube. Strong. Used to reinforce some sports equipment.
Why are metals malleable?
Metal ions are held in a lattice by forces that attract them to a sea of delocalised electrons. When a large enough force is applied layers of metal ions slide over one another but delocalised electrons are free to move so overall no bonds are broken.
What is a material made from nanoparticles called?
Nanoparticulate
Risks of nanoparticles
- May be breathed in, absorbed by skin or pass into cells
- May take a long time to break down once released into environment and toxic substances may stick to their surfaces
- Harmful to health and environment in ways difficult to predict, with risks difficult to determine
What is bonding in a simple molecule like?
- Covalent bonds involve electrostatic forces of attraction but the forces are between the nucleus of each bonded atom and the shared electrons
- Covalent bonds are strong. Intermolecular forces are weak.
What is a phase?
A substance in the solid, liquid or gas state.
What is the mobile phase in paper chromatography?
A solvent in the liquid state
What is thin layer chromatography?
Same way as paper chromatography, but stationary phase is a thin layer of silica or alumina powder spread over a plate of glass or plastic
What are Rf values?
Compare the different spots on a chromatogram
What is the mobile phase in gas chromatography?
Inert carrier gas such as nitrogen
What does gas chromatography do?
Separates components and measures their amounts
What happens in gas chromatography?
- Sample is turned into gas state and injected into column
- Different components take different times to travel through the column, depending on how strongly they bind to the stationary phase
- A detector sends a signal to a computer as each component leaves the column
- The computer produces a chromatogram in which each component is a peak plotted against the travel time
How to calculate Rf values?
Distance travelled by substance/distance travelled by solvent
What are the advantages of thin-layer chromatography?
Quicker, more sensitive, there are more choices of stationary phases and solvents to use
How to choose separation method?
- Insoluble and soluble substance -filtration
- A solute dissolves in solvent - crystallisation or simple distillation
- Two or more liquids-fractional distillation
- Coloured soluble substances- paper or thin-layer chromatography
What is a diamond like?
- Transparent and very hard
- Exists as a giant covalent structure where each carbon atom is covalently bonded to 4 other carbon atoms
- Has very high melting point
- No delocalised electrons as all valence electrons are shared so it doesn’t conduct electricity.
What is an allotrope?
Different forms of an element in the same state but with different atomic arrangements
What is graphite like?
- Grey-black and soft
- Giant covalent structure where each carbon atom is covalently bonded to three other, so one electron is not shared so it becomes delocalised and is free to move through the structure.
- It conducts electricity even though it is a non-metal. Has a layered structure
- Atoms in each layer form interlocking hexagons
- Very high melting point
- Forces between layers are weak so layers can slide over easily
- Graphite is hence slippery, used in pencil.
Difference between diamond and graphite
Diamond bonded to 4 graphite 3. Diamond is transparent and very hard , graphite is very-black and soft
Examples of allotropes of carbon
Diamond, graphite, graphene, fullerenes
What is graphene like?
A single layer of graphite. Almost transparent. Extremely strong and conducts electricity.
What is a fullerene like?
Comes from large family of carbon allotropes and the molecules are shaped like tubes or balls.
What is a buckyball?
- Resembles sheet of graphene closed to make a hollow ball
- But carbon atoms may be in pentagons as well as hexagons.
- Have potential uses as lubricants with molecules acting like tiny ball bearings
- Small size allows buckyballs to pass through cell membranes and might deliver medical drugs directly to cells one day.
What happens when a substance melts?
Some bonds break going from the solid to the liquid state
What happens when a substance boils?
All remaining bonds bream going from the liquid to the gas state
When do substances have high melting points?
If they have many strong bonds in the solid state
When do substances have high melting points?
If they have many strong bonds in the liquid state
What happens when a substance condenses?
Some bonds form going from the gas to the liquid state
What happens when a substance freezes?
Many bonds form going from the liquid to the solid state
How is stored chemical energy transferred to the surroundings?
Usually by heating , when chemical bonds form
Relative strength of a metallic bond
Strong
Relative strength of an ionic bond
Strong
Relative strength of a covalent bond
Strong
Relative strength of intermolecular forces
Weak
Which substance are usually in the solid state at room temp?
Metals, ionic compounds, giant covalent substances
What state are simple molecular substances in at room temp?
Liquid or gas or solid that is easily melted
What does the difference between malleable and brittle depend on?
How easily particles in the substance can change their positions in the lattice structure.
Why are other substances brittle?
- Giant covalent structures contain very many atoms held together by strong covalent bonds
- If large enough force applied many covalent bonds break at once so the substance breaks
- Similar situation for ionic compounds.
Simple molecules and polymer molecules are attracted to each other by what? Are they brittle or malleable?
- Weak intermolecular forces which are easily broken
- In solid state and arranged in lattice they may be brittle. If molecules
Why do some substances conduct electricity?
If it has charged particles that can move. Metals conduct in liquid and solid state. Simple molecules, most polymers and most substances with a giant covalent structure do not conduct electricity as no delocalised electrons.
Do ionic compounds conduct electricity?
Contain oppositely charged ions. Free to move in liquid state (molten) or when dissolved in solution but not in solid state. So conducts when molten or in solutions but not when solid
How big are nanoparticles?
1nm-100nm consists of just a few hundred atoms
What do nanoparticulate materials have?
Different properties to the same substance in bulk
What is the small size of nanoparticles useful for?
New paints, cosmetics, medicine
What are many nanoparticle properties due to?
Their very large surface area compared to with the same substance in bulk
What developments can nanoparticularw properties lead to?
New catalysts to speed up industrial chemical reactions. Self-cleaning windows, oven and clothes
What are ionic bonds?
Strong electrostatic forces of attraction between oppositely charged ions
What is a molecule?
Particle in which non metal atoms are joined together by covalent bonds
What is a simple molecule?
Contains few atoms that are covalently bonded but has weak intermolecular forces that are easily overcome
What do giant covalent structures consist of?
Many non-metal atoms joined by covalent bonds and arranged in a repeating regular pattern called a giant lattice.
Structure of metals
Giant metallic lattice
How are metallic bonds formed?
vElectrons leave outer shells forming a sea of electrons around positively charged metal ions. They are delocalised electrons.
What are metallic bonds?
The strong electrostatic forces of attraction between the delocalised electrons and the closely packed, positively charged metal ions.
