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Elements,
isotopes
and

ionisa/on
energies





Objec/ves

Must

State
that
12C
is
used
as
the
standard
measurement
of
rela/ve

masses.



Should

Define
terms
rela/ng
to
isotopic
and
atomic
mass,
molecular

mass
and
formula
mass.



Could

Use
data
such
as
rela/ve
abundances
to
calculate
rela/ve
atomic

mass.







1

Page 2

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Defini/ons


is
the
mass
of
an
atom
of
a

single
isotope
rela/ve
to
1/12th
of
a
12C
atom.




is
the
weighted
mean
mass
of

an
atom
of
an
element
rela/ve
to
1/12th
of
a
12C

atom,
taking
into
account
isotopic
abundances.



This
is
the
figure
usually
quoted
on
a…

Page 3

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Worked
example

Chlorine
has
2
isotopes
which
occur
naturally.

These
are
35Cl
and
37Cl.


The
Ar
of
chlorine
is
given
on
the
periodic
table

as
35.5
­
this
is
because
75%
of
the
atoms
that

exist
are
the
isotope
35Cl
and
25%
of
the
atoms

are
37Cl.




(!"#$$ %&")'(("#$$…

Page 4

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Calcula/ng
Ar
-
answers

1. Calculate
the
Ar
of
naturally
occurring
neon
if
the

composi/on
is
90.9%
neon
20,
0.3%
neon
21
and

8.8%
neon
22.



(!"#! $"" %&")'("#($"" %&$) + ()#) $"" %&&)*&"#&
2. Calculate
the
Ar
of
naturally
occurring
copper
if
the

composi/on
is
69%
copper
63…

Page 5

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5

Page 6

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Mark
Scheme





6

Page 7

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Mark
scheme





7

Page 8

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Mark
scheme





8

Page 9

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Mark
scheme





9

Page 10

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10/12/2011




Mark
scheme





Ionisa/on
energies





10

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