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) (c) doc band   (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) (c) doc b ,  (ii) dot and cross diagram of the water molecule  ,

(iii) and (iii) space filling model of water H2O

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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