Module 4: Section 1 Flashcards
What does a general formula show you?
Shows an algebraic formula that can describe any member of a family of compounds.
What does an emprirical formula show?
The simplest whole number ratio of atoms in each element in a compound.
What does a molecular formula show you?
The actual number of atoms of each element in a molecule.
E.g butan-1-ol = C4 H10 O
What does a structural formula show you?
Shows the arrangement of atoms carbon by carbon, with attached hydrogen and functional groups.
E.g CH3CH2CH2CH2OH
What does a skeletal formula show you?
Show she bonds of the carbon skeleton only, with any functional groups.
What does a displayed formula show you?
Shows how all the atoms are arranged, and the bonds between them.
What is a homologous series?
A group of organic compounds that have the same functional group and general formula.
What is a functional group?
Group of atoms in a molecule responsible for the characteristic reactions of that compound.
What are aromatic compounds?
Compounds that contain a benzene ring.
What are aliphatic compounds?
Compounds containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings.
What is a saturated compound?
Compounds containing only carbon-carbon single bonds.
What are unsaturated compounds?
Unsaturated compounds have carbon-carbon double bonds, triple bonds, or aromatic groups.
How can 2 molecules be isomers?
If they have the same molecular formula, but the atoms are arranged differently.
What is the general formula for alkanes?
CnH2n+2
Are alkanes saturated or unsaturated?
Alkanes are saturated, all the carbon-carbon bonds are single bonds
What shape do all alkane molecules have, and what bond angle?
In alkanes molecules, each carbon atom has 4 pairs of bonding electrons around it. They all repel another equally.
Tetrahedral shape. 109.5°
What affects boiling points of alkanes.
BPTs of an alkane depends on size and shape.
Alkanes have covalent bonds inside the molecules.
There are induced dipole-dipole interactions between molecules.
The longer the carbon chain, the stronger the induced dipole-dipole interactions, due to more surface contact.
A branched alkane has a lower bpt, as it can’t pack closely together and have smaller molecular surface areas.
What is produced when you burn (oxidise) alkanes in oxygen?
You produce carbon dioxide and water.
Combustion of propane:
C3H8 + 5O2 —-> 3CO2 + 4H2O
What is an alkly group?
Fragment of a molecule with general formula CnH2n+1
What are the 2 types of isomers?
- Structural isomers
2. Stereoisomers
What are the 3 different versions of structural isomers?
- Chain isomers (straight chain or branched)
- Position isomers (functional group attached differently)
- Functional group isomers (same atoms can be arranged into different functional groups)
Why do alkanes make excellent fuels?
Alkanes release lots of energy per mole as they have lots of bonds to react in a combustion reaction.
What is produceed when you burn alkanes in limited oxygen?
You produce carbon monoxide and water.
Incomplete combustion of methane:
2CH4 + 3O2 —-> 2CO + 4H2O
Why is carbon monoxide a risk?
CO is poisonous. It binds to the haemoglobin in your blood better than the oxygen. This means that less oxygen is transported around your body, and this leads to oxygen deprivation.
What is bond fission?
Breaking a covalent bond.
What is heterolytic bond fission?
What does it produce?
Covalent bond breaks unevenly, and 1 bonded atom gets both electrons. It produces a positively charged cation and a negatively charged anion.
What is homolytic fission?
What does it form?
Covalent bond breaks evenly, and each bonded atom recieves 1 electron. It produces 2 free readicals.
Halogens react with alkanes in what type of reaction?
Photochemical reaction.
requires UV light
What happens in a free-radical substitution reaction?
Hydrogen atom is substituted by chlorine or bromine
What are the 3 stages in a free-radical substitution reaction.
- Initiation (free radicals are made by homolytic fission)
- Propogation (radicals are used and remade)
- Termination (free radicals are mopped up)
What is a common problem with free-radical substitution?
You always end up with a mixtuire of products.
You can have isomers, as substitution can occur anywhere along the carbon chain.
What is the general formula for alkenes?
CnH2n
Are alkenes saturated or unsaturated?
Unsaturated hudrocarbon, as they contain atleast one C=C.
How is a sigma bond formed?
Why do sigma bonds have a high bond enthalpy?
2 s-orbitals overlap.
There is a high electron density between the nuclei.
There is a strong electrostatic attraction between the nuclei and the shared pair of electrons.
Sigma bonds have a high bond enthalpy.
How is a pi bond formed?
Why are pi bonds weaker than sigma bonds?
Side overlap of 2 p-orbitals.
1 pi bond sits above and 1 below the molecular axis.
Pi bonds are much weaker than sigma bonds beacuse the elctron density is spread out.
Electrostatic attraction bewteen the nuclei and shared pair of electrons is weaker.
Why are alkenes more reactibe than alkanes?
Alkanes only contain sigma bonds, which have a high bond enthalpy.
Alkanes are also non-polar, so they dont attract neucleophiles or electrophiles.
What types of bonds does a C=C contain?
A C=C bond contains a sigma bond and a pi bond.
Why are pi bonds likely to be attacked by electrophiles?
C=C contains 4 electrons, so has a high electron density. This will attract electrophiles, as they are keen to accept electrons.
The pi bond in the C=C bond sticks out above and below the axis. This makes it easier to attack.
What does it mean if you say the atoms are all planar?
They all lie in the same plane.]
What is the shape of the carbon atoms in the C=C, and the atoms bonded.
Also give the bond angle.
Trigonal planar.
120 degrees
What causes stereoisomers?
Restricted rotation around a C=C.
What is the difference between a Z-isomer and a E-isomer?
Z-isomer = has the same groups either above or below the C=C. E-isomer = has the same groups positioned across the C=C.
How do you decide which stereoisomer is assigned Z amd E when they have 4 different groups attached?
Larger atomic no = higher priority.
E-ismoer = higher priority groups positioned across the C=C Z-isomer = higher priorty groups positioned on the same side of the C=C
What is the difference bewtween cis and trans isomers?
Cis = groups on the same side of the C=C Trans = groups on the opposite sides of the C=C
What happens during electrophilic addition?
Alkene double bonds opens up (pi bond is broken) and electrophiles are addeds to the carbon atoms.
Why are C=C attacked by electrophiles?
The double bond has lots of electrons, so attracts electrophiles and is attacked by them.
What is an electrophile?
Electron-pair acceptor.
What occurs in a hydrogenation reaction?
Hydrogenation is an addition reaction, where hydrogen is added across a C=C. It produces an alkane
What conditions are needed for a hydrogenation reactions?
150 degrees celsius.
Nickel catalyst.
What happens in a halogenation reaction?
Halogens react with alkenes to form dihaloalkanes.
Its and electrophilic addition reaction.
How can you test for C=C?
When you shake an alkene with bromine water, the solution decolourises.
Br2 is added across the doubel bond to form a colourless dibromoalkane.
What are hydration reactions used for in industry?
Used to make alcohols, from alkenes.
What conditions are needed for a hydration reaction?
300 degrees celsius.
65 atm
H3PO4 (Phosphoric (V) acid catalyst)
What happens when you add hydrogen halides to an alkene?
Hydrogen halides (HBr, HCl, HI) react with alkenes to form haloalkanes. This is another electrophilic addition reaction.
What is Markownikoffs rule?
When H-X is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon with the most hydrogens already attached.
When are carbocations more stable?
Carbocations with alkyl groups attached are more stable than those with hydrogen atoms attached.
What occurs in an addition polymerisation reaction?
Monomers are joined together to make polymers.
Why arent polymers biodegradable?
Polymers are very unreactive, so arent biodegradable.
What are 3 ways to get rid of waste plastics?
- Bury it
- Reuse it
- Burn it
When do we bury waste plastics?
Landfills are used when plastic is difficult to seperate from other waste.
Give 2 examples of reusing waste plastics.
- It can melyed/remoulded into new, useful items.
2. Some can be cracked into new monomers.
What are the benefits of burning waste plastics?
When waste plastics are burnt the heat can be used to generate electricty.
Polymers containing chlorine produce HCl when theyre burned. How can waste gases be removed?
Waste gases are passed through scrubbers, which neutralise gases by reacting them with a base.
