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1d. Key to styles of diagrams, comparison of
chemical bonding
diagrams, dot and cross, 2D and 3D models for ionic, covalent and metallic
structures
Doc
Brown's Chemistry: Chemical Bonding and structure GCSE/IGCSE/O/IB/AS/A US grade
9-12 Level Revision Notes
There are lots of dot and cross
diagrams i.e. Lewis diagrams of bonding situations
Comparing diagrams and models
for ionic and covalent bonding
(a) Ionic
bonding e.g. diagrams for sodium chloride
(i)
 
or
2D formation electron transfer diagram
(ii)
 and
(iii) 
|
Diagrams and models for
ionic compounds |
| 'Pros& cons' \
diagram or model |
(i) 2D electronic o
and x Lewis diagram |
(ii) 3D ball and
stick model |
(iii) close packed 'space
filled' model |
| Diagram or model
good at showing ... |
electron structure
of ions - detailed picture of the ionic bond
how formed |
3D structure,
regular arrangement of ions, how ions arranged, charges on the ions,
the relative numbers and type of ions |
3D structure,
charges on ions, 2D arrangement of ions on front face of diagram (3D
view not as clear on positions of ions - masking effect), but shows
close proximity of ions packed together - real relative size of ions |
| diagram or model no
good at showing ... |
No
2D or 3D structure can be appreciated in terms of size and position
of ions ?? |
the close proximity
of ions - suggest spaces that don't exist, lines suggests
electrostatic bonds are directional - but actually act in all
directions |
Not easy to see 3D
arrangement of ions beyond the 'front face' of the diagram |
Ionic formulae are often the
empirical formula e.g. sodium
chloride is NaCl
(b) Covalent - small molecules
e.g. water
(i) 
, (ii)
,
(iii)
 and (iii)
All diagrams should match the
molecular formula e.g. for water
it is H2O
|
Diagrams and models for
covalently bonded elements or compounds |
| |
2D Displayed formula |
2D electronic o &
x Lewis
diagram |
3D ball and stick
model |
3D space filled
model |
| Good to show |
which atoms are in a
molecule and how they are connected with covalent bonds - single,
double or triple |
electron structure
of molecules - particularly the bond details of which atoms
contribute which electrons to the bonds |
the bonds, spatial
arrangement of atoms in the molecule - the overall shape |
the real relative
size of atoms based on the space occupied by the electron clouds |
| No good to show |
3D structure, no
details of shape of molecule, where the electrons came from to form
the bond |
relative size of
atoms or how they are arranged in space |
no electronic
detail, size of atoms, spaces suggested that don't exist - the balls
are not the true relative size |
no electronic
detail, bonds not shown |
Its worth making the following comments on the different
representations of simple covalent molecules of >2 atoms
So, reminders: know your structural and displayed formulae
(i) Dot and cross diagrams are good for
showing the electronic detail of the structure, and whether the bonds are
single (ox) or double (ox) etc. However, it gives no idea on the
shape of the molecule i.e. the 3D spatial arrangement of the bonds and atoms
(its effectively a 2D diagram, but the molecule might not be flat!) and no
information about the relative size of the atoms.
(ii) Displayed formulae clearly shows how the atoms are bonded together,
e.g. the
arrangement of the three N-H single bonds, but only gives a 2D view of the molecule.
(iii) It needs a 3D ball and
stick model diagram to give an idea of the spatial arrangement of the atoms,
but not the relative size of the atoms. A space filling model would give the
shape of the molecule and the relative size of the atoms. However, neither
of these two models show any electronic details of how the
covalent bond is formed.
What
next?
Recommend next:
A brief
comparison of types of bonding and structure
Sub-index for:
Part 1
Introduction to
chemical bonding - why? how? and patterns
Index for
ALL chemical
bonding and structure notes
Perhaps of interest?
Determining empirical formula and formula mass of a compound from reacting masses
Using
moles to calculate empirical formula & deduce a compound's molecular formula
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