Alkanes Flashcards
HNC exam preparation for Outcome 3 Fundamental Chemistry
What is the hybridised state of alkanes?
sp3 hybridised
What is the geometry and bond angle in alkanes?
Tetrahedral
109.5 degree bond angles
What condition(s) do alkanes require to react with halogens?
UV light or sunlight
Room temperature
Name the main type of reaction alkanes undergo…
Free radical chain reaction
a. k.a. free radical substitution
a. k.a. halogenation substitution of alkanes
Define a substitution reaction…
The replacement of an atom or group in a molecule by a different atom or group
Name the three steps in the process of free radical chain reactions of alkanes…
1) Initiation
2) Propagation
3) Termination
Summarise homolytic fission…
When a covalent bond breaks, each of the atoms gets back the electron they had invested in the original bond. These electrons are known as free radicals
When a covalent bond breaks and one atom gains both the electrons from that original bond ( e.g. with H-X, the halogen becomes an anion while the hydrogen forms a cation), what is this known as?
Heterolytic fission
What are electrophiles?
+ve ions or partially +ve atoms (electron ‘poor’ species) that will readily accept a pair of electrons in the formation of a covalent bond
Are anions and partially -ve atoms electrophiles or nucleophiles?
Nucleophiles
electron ‘rich’ meaning they will readily donate a pair of electrons to form a covalent bond
In the free radical substitution reaction involving ethane (C2H6) and chlorine (Cl2) in UV light, state the three products that will be present at termination…
butane (C4H10)
chlorine (Cl2)
chloroethane (C2H5Cl)
If Br2 (orange colour) is added to a test tube containing an alkane e.g. ethane, what colour change is observed?
No colour change
alkanes are saturated therefore don’t readily react
