I have decided to write a post about my most successful pupil crowd pleaser – no not potassium and water, it’s over too quickly. Growing crystals has become my go to project to reel in the budding chemists. It really is a magical experience although the fiddily process of looping the seed crystal is painful for my clumsy spade like hands. However hand a seed crystal over to the pupils and in no time they’ve set up and are taking the first of many pictures over the coming days and weeks. This is where mobile devices come into their own, pupils can take daily pictures of the crystals and look at how they grow over a period of time. Last year we really focused on crystal growing as it was the international year of crystallography. The International Union of Crystallography ran a world wide crystal growing competition and it was also the focus of the RSC global experiment. This synchronised approach by both the RSC and IYCr allowed us to focus on crystal growing withdifferent year groups and abilities with varying success but definitely enthusiasm and fun!
Patterns are all around us, look at a tiled roof, wall paper and even wind ripples in sand. The repetitive nature of a pattern is repeated at atomic level in crystals. Crystals are solids composed of atoms, ions, or molecules arranged in a pattern that is periodic in three dimensions. Crystallography is the science of determining the arrangement of the atoms in a crystalline structure by studying diffraction patterns when x ray’s interact with each atoms electron cloud. Nearly every solid can crystallise which means that theoretically we can obtain ‘a picture’ of the arrangement of atoms in a substance. However, I remember the rows of beakers littering PhD students desks (as they tried different solvents and different evaporating times)and the dejected look on their faces as they returned from the crystallographers room – growing suitable crystals is an art in itself !
It was William Bragg who allowed us to investigate crystals. Bragg’s law on the diffraction of X-rays by crystals makes it possible to calculate the positions of the atoms within a crystal from the way in which the X-ray beam is diffracted. The technique of crystallography has underpinned some of the best science of the last century. It has paved the way for the elucidation of the structures of many biological molecules with the most notable being Watson and Cricks structure of the DNA double helix, with those preliminary experiments carried out by Rosalind Franklin. Crystallography provides essential information in so many scientific fields such as materials science, medicinal chemistry and geology to name a few. And science likes to reward those crystallographic discoveries – check out the link below to see the crystallography based Nobel prizes. Only two years ago Dan Shechtman was awarded the prize for his work on quasicrystals which are crystalline structures that break their periodicity. Normal crystal structures can be described by one of 230 space groups, which describe the rotational and translational symmetry present in the structure. Shechtman rapidly cooled an alloy of aluminum and manganese and found that it showed the forbidden five fold symmetry. He had to fight the established scientific beliefs about crystals to establish this new field and I love that he apparently said when analysing his crystallographic data – “There can be no such creature.”
Check out the Guinness Book of Records attempt at building a replica of crystalline sodium chloride. It’s 3m tall and has nearly 40,000 balls ( representing the sodium and chloride ions) and nearly 12km of sticks. The real beauty of the lattice is that it gives us a visual representation of what’s really in a crystal of salt, allowing us to the bask in the order and symmetry of our chemical world !