Chemistry Level 7 - Bonds and Reactions Flashcards
(23 cards)
what is heterolytic fission?
- breaking of a covalent bond where one of the atoms in a bond takes both of the shared electrons
- results in formation of an anion and cation
how can heterolytic fission be represented?
X - Y -> X+ + Y-
eg. H - Cl -> H+ + Cl-
what is homolytic fission?
- breaking of a covalent bond where the bond breaks equally
- each atom receives one electron from the shared pair
- results in formation of free radicals
what are free radicals?
- particles that have one or more unpaired electrons in their outer shell
- formed when bonds break
how can homiletic fission be represented?
X - Y -> X* + Y*
eg. Cl - Cl -> Cl* + Cl*
what homologous series can undergo free radical substitution?
alkanes
what happens in free radical substitution?
a hydrogen atom gets substituted by a halogen
what is required for a free radical substitution reaction to take place?
UV light
what are the three steps in free radical substitution?
- initiation
- propagation
- termination
draw out each step in a free radical substitution reaction when methane is reacting with chlorine
initiation:
Cl - Cl -> Cl * + Cl * (UV light)
propagation:
Cl * + CH4 -> CH3 * + HCl
CH3 * + Cl2 -> CH3Cl + Cl *
termination:
CH3 * + Cl * -> CH3Cl
what is electrophilic addition?
- addition reaction where an electrophile attacks a double or triple bond in a molecule
- leads to addition of atoms or groups across that bond
what is an electrophile?
positively charged particle that accepts electron pairs when forming covalent bonds
what is nucleophilic substitution?
- substitution reaction where a nucleophile replaces an atom bonded to a saturated carbon atom
- results in new bond being formed
what is a nucleophile?
negatively charged particle which donates electron pairs when forming covalent bonds
what are examples of oxidising agents?
- Tollen’s Reagent
- Acidified Potassium Dichromate (Cr2O2 7- / H+)
what are both oxidising agents used for?
to oxidise an alkanal to an alkanoic acid
what is required for oxidising agents to work?
heat
what is an example of a reducing agent?
lithium aluminium hydride (LiAlH4)
what does LiAlH4 reduce?
- alkanals to primary alchohols
- alkanones to secondary alcohols
what are reducing sugars?
sugars that contain a carbonyl group
what do reducing sugars do?
- reduce other substances, such as metal ions in a certain test and in the process, they themselves get oxidised
- eg. Benedict’s Test - reducing sugar reduces Cu2+ ions to Cu+
what are examples of reducing sugars?
glucose, fructose, lactose and maltose
what is an example of a non-reducing sugar?
- sucrose
- unable to reduce metal ion
