My name is Katie, I'm currently studying natural
sciences at Murray Edwards college, Cambridge.
I've just finished my second year of the course
and I've chosen to specialise in Chemistry.
So today I'm going to talk about the interview
structure for when I applied 3 years ago.
For physical natural sciences. and then go
through an example question so you can see
what kind of level they are expecting you
to be at and what the best way it is to answer
these questions.
So when you apply for natural sciences, you
should specify on the SAQ form whether you
are applying for physical natural sciences
or biological natural sciences.
This doesn't actually limit you once you can
get to Cambridge.
You could still change your mind later.
But it's more to decide what kind of interview
structure they decide to give you.
So I applied for physical natural sciences
therefore I had two interviews with my college.
This does vary between colleges though.
But for mine, I had a physics based interview
and a chemistry based interview.
My physics based interview was with me and
my physics supervisor and a materials supervisor.
They mainly went through more mathematical
questions.
I didn't have to sit an official maths test
but they brought along with them a list of
maths questions on a piece of paper which
was laid out in a very similar way to a test.
I worked through the questions with them and
they could basically see how I thought about
thought through questions on a maths test.
We then discussed a few things on my personal
statement and a couple more questions based
on more physics based topics.
So the second interview I had was with a chemistry
supervisor and a geology supervisor.
This obviously covered mainly chemistry questions,
a few geology ones and they also asked a couple
of biology related questions which were to
do with my personal statemnet.
The chemistry interview didn't contain nearly
as much maths.
It was a lot more about how I understood chemistry
there were some diagams I had to draw or interpret.
They were some graphs, some data.
They wanted to see that I could both remember
a lot of stuff from A-level chemistry but
apply it to different situations and actually
understand the reasoning behind it.
So now to an example question.
This was a question I was given in my chemistry
interview.
I believe it's actually quite a popular question
between different colleges because I've heard
other people having the similar questions
too.
It's actually a reasonably simple question.
Explain the trends in bond length and bond
dissociation energy for the halogens.
Explain why fluorine doesn't fit the trend.
They don't expect you to remember exactly
what the trend is.
They gave me a table data which stated the
bond energies and the bond lengths for each
of the molecules of interests.
I've drawn out this table again for you.
It looks like this.
You don't need to look into details into numbers.
All they want to see is that you could understand
the trend and explain the trend behind this.
First thing I did obviously was look at data
and visually think about how this look on
a graph.
How would you visualise this?
So if you think about how it looks on a graph,
quite simply the bond length for fluorine
is 143 which is quite small and it increases
all the way upto iodine at 266.
It's a reasonably linear increase.
So the first part of the question is explain
the trend in bond length.
This is actually very simple.
The atoms are bigger so the molecule must
be bigger.
But the more challenging bit of this question
was the second half of the question about
the bond dissociation energy.
So this isn't a perfectly linear trend.
For iodine to chlorine, there is quite a steady
increase as you go down from chlorine down
to iodine, the bond dissociation energy decreases.
This makes sense when you think about the
bond length the first part of the question.
Often the the question with several parts
you can use the earliest of the questions
to help later bits of the question.
We knew from the first half the question that
the bond length were increasing so it makes
sense that the bond dissociation enthalpy
is decreasing because atoms are further apart.
So it is easier to break the bond.
But the pretty hard bit is what happens with
fluorine?
Because fluorine actually has a lower bond
dissociation enthalpy than chlorine which
doesn't fit the trend.
It should be higher.
Let's comes a bit down to the size of the
atoms.
Fluorine is a very small atom.
So they are put close to together, their interactions
between all the electrons around each of them,
the atoms, in iodine for example, they are
much further apart so any repulsive forces
between the electrons is not significant enough
to really affect the bond dissociation energy.
But for fluorine, the two atoms are very close
together.
To think about the diagram you often draw
at A-Level for halogens, we draw dots and
crosses around the edges of each atom.
You can see that the electrons on each of
the atoms are quite close together and they
can repel.
And this repulsive force is actually easier
to break the bond than you would expect.
Therefore, the bond dissociation energy is
lower.
So when you look at it that way, actually
it's quite a simple question.
You have to break it down to different parts
and think logically and through each of the
questions.
