12.1- ALKANES Flashcards
What type of hydrocarbons are alkanes?
saturated
Why are alkanes described as saturated hydrocarbons?
contain only carbon-carbon and carbon-hydrogen single bonds
What are alkanes among reactivity?
among the least reactive organic compounds
What are alkanes used as? (3)
fuels and lubricants and as starting materials for a range of other compounds
What is the main source of alkanes?
crude oil
What is the general formula for alkanes?
CnH2n+2
In what form can hydrocarbons be in?
unbranched chains, branched chains, or rings
What are unbranched chains often called?
straight chains
What is the angle of the C-C-C?
109.5 degrees
As the C-C-C is 109.5 degrees what does this mean?
chains are not actually straight
In an unbranched alkane how many hydrogen atoms are attached to each carbon atom?
each carbon atom has two hydrogen atoms except the end carbons which have one extra
What is the general formula for ring alkanes?
CnH2n
Why do ring alkanes have a general formula of CnH2n?
end hydrogens not required
Where is the alkanes named from?
the root
What does the root of an alkane tell us?
the number of carbon atoms
What does the suffix -ane tell us?
denotes an alkane
What must you first find when naming a hydrocarbon with a branched chain?
must first find the longest unbranched chain
What does the longest unbranched chain of a branched hydrocarbon give?
gives the root name
How are the branches/side chains named?
by prefixes e.g. methyl-, ethyl-, propyl-
What do numbers tell us when naming a branched hydrocarbon?
which carbon atoms has side chains are attached to
What alkanes have no isomers?
methane, ethane and propane
How does the number of possible isomers change depending on the number of carbons in the alkane?
possible isomers increases with the number of carbons on the alkane
What is the polarity of alkanes like?
almost non-polar
Why are alkanes almost non-polar?
because the electronegativites of carbon and hydrogen are so similar
As alkanes are non-polar what are the only intermolecular forces between their molecules?
weak van der Waals forces, larger the molecule, stronger the van der Waals forces
What happens to boiling point of alkanes as there’s increasing intermolecular forces?
boiling point increases as the chain length increases
What state are shorter chain alkanes at room temperature?
gases
At about what chain length do alkanes become solids at room temperature?
18 carbons
What feel do the solid alkanes have?
waxy feel
What is the boiling point of alkanes with branched chains like in comparison to straight chain alkanes with the same number of carbon atoms?
lower melting points
Why do alkanes with branched chains have lower melting points in comparison to straight chain alkanes with the same number of carbon atoms?
they cannot pack together as closely as unbranched chains so van der Waals forces not so effective
Are alkanes soluble in water?
no
Why are alkanes not soluble in water?
because water molecules are held together by hydrogen bonds which are much stronger than van der Waal’s forces that act between alkane molecules
What do alkanes mix with?
other relatively non-polar liquids
How reactive are alkanes?
relatively unreactive
What are the bonds in alkanes like?
strong carbon-carbon and carbon-hydrogen bonds
What do alkanes not reactive with?
acids, bases, oxidising agents and reducing agents
What do alkanes burn and react with under suitable conditions?
burn and react with halogens under suitable conditions
What do alkanes burn in a plentiful supply of and produce what?
burn in a plentiful supply of oxygen to form carbon dioxide and water
