Basic Concepts And Hydrocarbons Flashcards
What is a functional group?
The group of atoms within a molecule that is responsible for the characteristic reactions of a molecule
What is a homologous series?
A family of compounds that have the same functional group and general formula. Consecutive members of a homologous series differ by CH2
What is the general formula of an alcohol?
CnH2n+1OH
What is the general formula of alkanes?
CnH2n+2
What is an aromatic compound?
An organic compound that contains a benzene ring
What is an aliphatic compound?
An organic compound that contains carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
What is an alicyclic compound?
An organic compound that consists of carbon and hydrogen joined together in a non-aromatic ring
What is the general formula of an alkyl group?
CnH2n+1
What are structural isomers?
A molecule with the same molecular formula as another molecule, but with the atoms connected in a different way (structural formula is different)
What are the 3 different types of structural isomers?
- Chain isomers
- Positional isomers
- Functional group isomers
How will chain isomers be different?
Molecules will have different arrangements or the carbon skeleton
How will positional isomers be different?
Functional group attached to different carbon atom
How will functional group isomers be different?
Same atoms arranged into different functional groups e.g. hex-1-ene and cyclohexane
Are alkanes saturated or unsaturated?
Saturated
Name the first 10 stems for number of carbon atoms
Meth, eth, prop, but, pent, hex, hept, oct, non, dec
What is the bond angle and shape around a carbon atom in an alkane?
109.5, tetrahedral shape
What is a sigma bond?
A type of bond formed when 2 orbitals overlap directly between the bonded atoms
What is the strongest type of covalent bond? Why?
Sigma bonds: high electron density between nuclei means there is a strong electrostatic attraction between the nuclei and shared pair of electrons, so sigma bonds have high bond enthalpy. The bonded atoms are free to rotate around the sigma bond as whichever way the atoms point, the atomic orbitals between them will always overlap
Explain the reactivity of alkanes.
Pretty unreactive - due the sigma bonds between C-C and C-H which all have a large bond enthalpy, making them very strong and therefore difficult to break. Bonds are also non-polar so won’t attract any positively or negatively charged particles to react with them.
What affects the boiling point of an alkane?
Size and shape affects intermolecular forces
Why does the length of a carbon chain affect boiling point?
Between molecules there are induced dipole-dipole interactions. Longer chain = more induced dipole-dipole interactions. This is because they have a larger molecular surface area so there is more surface contact between the molecules and there are more electrons to interact. So as molecules get longer it takes more energy to overcome the induced dipole-dipole interactions and separate them
Why does branching affect the boiling point of an alkane?
Branched chain alkane has a lower boiling point than its straight chain isomer. Branched chains can’t pack as closely together and they have smaller molecular surface areas so induced dipole-dipole interactions are reduced
Why is carbon monoxide poisonous?
Oxygen in bloodstream carried by haemoglobin. CO better at binding to haemoglobin than O2 so less oxygen will reach your cells
What is heterolytic fission?
Bond breaks unevenly with one bonded atom receiving both electrons from the bonded pair. 2 different substances are formed: positively charged cation and negatively charged anion
What is homolytic fission?
Bond breaks evenly and each bonding atom receives one electron from the bonded pair. 2 electrically uncharged radicals are formed.
What is a radical?
A particle with an unpaired electron
What do curly arrows show?
The movement of a pair of electrons
What are photochemical reactions? Give an example.
Reactions that are started by light. E.g. when halogens react with alkanes to form haloalkanes
What are the three stages of a radical substitution reaction?
Initiation, propagation, termination
What is photodissociation?
When sunlight provides enough energy to break a bond by homolytic fission
What are problems with radical substitution?
- You get a mixture of products (best way of reducing this is to have a excess of the alkane
- Substitution can take place at any point along the carbon chain
What is the general formula of an alkene ?
CnH2n
Are alkenes saturated or unsaturated?
Unsaturated
What is a double bond made up of?
A sigma bond and a pi bond
How is a pi bond formed?
When 2 p orbitals overlap sideways. Has 2 parts to it one above and one below the molecular axis due to the dumb-bell shape of the p-orbitals
Why are pi bonds weaker than sigma bonds?
Electron density is spread out above and below the nuclei. Therefore the electrostatic attraction between the nuclei and shared pair of electrons is weaker, so pi bonds have a relatively low bond enthalpy
Explain the reactivity of alkenes.
Pretty reactive because there are 2 pairs of electrons in the C=C double bond giving it a really high electron density. The pi bond also sticks out above and below the rest of the molecule, so the pi bond is likely to be attacked by particles that have a low electron density and can accept a pair of electrons (electrophiles). The low bond enthalpy of the pi bond also contributes to the reactivity.
What is the bond angle and bond name around a C=C?
Trigonal planer shape, 120 degrees
What are stereoisomers?
Have the same structural formula but a different arrangement in space
What is an E-isomer? What is a Z-isomer?
E: higher priority groups on opposite sides
Z: higher priority groups on the same side
What 2 requirements are there for a stereoisomer to exist?
- C=C double bond
- 2 different elements bonded to each carbon atom
What is cis-trans isomerism? What is a cis-isomer? What is a trans-isomer?
Special type of E/Z isomerism where the 2 carbon atoms either side of the double bond have at least 1 group in common.
Cis: 2 identical groups non the same side of the C=C double bond (e.g. both above)
Trans: 2 identical groups on opposite sides of the C=C double bond
What is an electrophile?
Electron pair acceptor
What is a nucleophile?
Electron pair donor
Conditions needed for an alkene to react with hydrogen to for an alkane?
Nickel catalyst and 150 degrees C
What is the test for unsaturation?
- Add 2cm cubed of orange bromine water to test tube
- Add 2cm cubed of unknown hydrocarbon to same test tube
- Stopper the test tube and shake
- If hydrocarbon is an alkene the solution will turn from orange to colourless
What conditions are needed for alkenes to be hydrated to become alcohols?
300 degrees C, pressure of 60-70 atm, solid phosphoric acid catalyst
How do you form the major product?
Hydrogen adds to the carbon with the most hydrogens already attached
What are the 3 ways of disposing of waste plastics?
Burying in landfill, recycling, burning as fuel
Why are polymers useful in everyday life?
Very unreactive
When is landfill generally used?
- When difficult to separate from other waste
- When not in sufficient quantities to make separation financially worthwhile
- When too difficult technically to recycle
How can plastics be recycled?
- Melted and remoulded
- Cracked into monomers which can be used as organic feedstock to make more plastics or other chemicals
What can burning waste plastics be used for?
The heat can be used to generate electricity
How are toxic gases controlled during burning of polymers, what is an example of a gas that has to be controlled?
Waste gases from the combustion are passed through scrubbers which can neutralise gases allowing them to react with a base. Polymers that contain chlorine e.g. PVC, produce HCl when they’re burned
What can biodegradable polymers be made from?
- Starch from maize and other plants
- Hydrocarbon isoprene
What are advantages of using renewable raw materials?
- Won’t run out like oil will
- If polymer is plant based CO2 released as it decomposes is the same as CO2 absorbed by the plant when it grew. With oil-based biodegradable polymer, carbon from the oil is being transferred to the atmosphere
- Over their ‘lifetime’ some plant based polymers save energy compared to oil-based plastics
What are the disadvantages of using biodegradable polymers?
- Still need the right conditions before they will decompose, therefore e have to be separated from non-biodegradable plastics
- More expensive than oil based equivalents
What is a use of a biodegradable polymer?
Plastic sheeting to protect plants from frost, in time starch is broken down by microorganisms and the remaining poly(ethene) crumbles into dust. No need to collect & dispose of old sheeting
What are potential developments to decrease the environmental damage caused by waste plastics?
- Continue to develop photodegradable polymers & introducing them into everyday use
- Developing better techniques for cracking polymers so recycling becomes more efficient
- Finding new ways of making polymers from plant-based substances to reduce the use of finite raw materials like crude oil
- Using processes with higher atom economy to reduce amount of waste produced during manufacturing processes
- Developing new, more efficient ways of sorting and recycling polymers
