What is this all about?
2014 has been designated by the UN as ‘International Year of Crystallography’, and this is one of many many projects that are being undertaken to promote crystallography far and wide.
What is crystallography?
Crystallography is the science that examines the arrangement of atoms within solids. As you get solids in all walks of life, so crystallography has impacts for every type of science!
How do we describe crystal structures?
You need three bits of information to construct the infinite array that any crystal structure is.
First – how big and what shape is your repeating cell.
Second – Symmetry of the atoms in the cell. Amazingly there are only 230 possible symmetries that can be found in three dimensional space.
Third – You need to know the coordinates within the cell of your basic set of atoms. These are then multiplied by the symmetry
With these three bits of information you can plug into any crystal drawing software to create the structure of your choice.
Find all these bits of information can be a very arduous process, and scientists employ a number of techniques to find these arrangements. Of course there are always deviations and strays from these perfect models. But that’s often where the science comes in!
Why are you using that silly Å unit?
The Angstrom (Å), is 1 x 10-10 m, or 0.0000000001 m. It’s widely used to crystallography as 1 Å is about the distance between an oxygen and hydrogen atom in a water molecule, so it’s a better scale for describing the arrangement of atoms.
Are you really going to have enough to describe a structure a day for a WHOLE year?
Yes, pretty easily. In fact narrowing it down to 365 will be the big challenge. As each structure is determined, the scientist that discovered them will put the structure (using the steps we introduced above) into an accessible database. Which database they place it into depend on the field they are working in. For instance structural biologist tend to post structures to the Protein Database (95,644 structures and counting) organic chemists will often post to the Cambridge Structural database (over 600,000 structures), inorganic chemists to the Inorganic Structural Database (over 80,000 structures) and Geologists will post to the American mineralogical database. But there’s a lot of overlap!
There’s also now the Open Crystallography Database project with 244,992 crystal structures and counting.