What is an element?

An element is a substance made up of atoms of only a single type.  We refer to elements by their name or sometimes their chemical symbol.  For instance, carbon = C, oxygen = O and sodium = Na. The most common elements in nature are, Hydrogen (H), Helium (He),  Oxygen (O), Carbon (C), Neon (Ne), Iron (Fe), Nitrogen (N), Silicon (Si), Magnesium (Mg), and Sulfur (S). Elements can be solids, liquids, or gases.  You may wonder why some element symbols don’t match their English names, this is because the symbols come from the element names in other languages. Na for Sodium comes from the Latin word “Natrium”.  Tungsten is a Swedish word, but the symbol for it, W, comes from the German word Wolfram. Chemistry is really an international science!

What are atoms?

Atoms are some of the smallest building blocks of all materials.  They’re really tiny! A single atom is 100 million times smaller than a pea!  To put it another way, there are over 70 billion billion billion (70 x 10^27) atoms in a typical adult person.

What are molecules?

Atoms of different elements often join together through chemical bonds to form molecules.  A molecule is the smallest form of a chemical substance. Famous molecules include things like DNA, table salt (NaCl), and sugar (glucose), but the world around us is made up of many more.

What is a crystal?

A crystal is a solid form of an element, molecule, or group of molecules.  In a crystal, molecules or atoms repeat over and over in a regular pattern.  The simplest repeat unit of these atoms and molecules is called a unit cell and this is what you see for each element we have selected for #IYPTCrystal. Another way of thinking about this is to imagine that in a brick wall, the unit cell would be a brick, and the whole brick wall would be the crystal.

Crystals are all around us in everyday life and grow naturally and also in laboratories around the world. They can be objects of desire such as diamonds and gems or less fancy items such as salt and sugar. They are often beautiful to look at, with very regular shapes and can be very small, visible only through a microscope, or very large such as in the giant crystal cave (Cueva de los Cristales) in Mexico.  Some crystals can be clear and transparent, others are vividly coloured. The shape and colour of the crystal is directly related to the atoms or molecules inside that crystal.

How do we see the atoms and molecules inside a crystal?

Atoms and molecules are too small to see with the naked eye, but scientists use X-rays to visualize what the atoms and molecules look like as they form a crystal.  This technique is called Crystallography. When crystals are zapped by X-rays, the X-ray light forms a pattern, unique to each crystal. Scientists use digital X-ray detectors to record the pattern and decode it to generate a view of the arrangement of atoms and molecules in the crystal.

Why is this useful?

Crystallography has been behind most of the key advances in medicines, transport, energy, and technology in the past 100 years. It tells us about the arrangement of atoms and the shape of molecules in a crystalline material and scientists need this information to help them make choices about how to use these atoms and molecules in our day-to-day lives.

What is a refcode and why does it matter?

You might notice that we tag each crystal structure with a unique ‘refcode’ which corresponds to its entry in the CSD. This is because there are nearly a million structures that we need to keep track of, and sometimes their scientific names can get quite long. Scientists who use the database need a quick, simple way to find the one structure they need! Gwenda Kyd has discussed this here : https://www.ccdc.cam.ac.uk/Community/blog/post-20/

How many crystal structures are there?

In 2019 the database hit one million structures! That means scientists have done one million experiments to understand the shape of molecules and to unlock the order of atoms inside the crystal. For more information on our countdown to one million, check out Seth Wiggin's blog: https://www.ccdc.cam.ac.uk/Community/blog/countdown_to_1_million/

How many elements have been included in a crystalline material?

To date, 93 of the 118 known elements have been observed in a crystalline material.  Some of these can crystallize as a single element (like sulphur or carbon) while others crystallize as part of a larger molecule (like the carbon, hydrogen and oxygen in sugar).   The remaining 25 are very challenging to work with - they are highly radioactive so most of them are not stable enough to hang around for long enough to grow into a crystal. For these elements we will pick interesting crystal structure made from different elements from the 93 elements that have been crystallised.

What are the top 10 elements that appear most frequently in the crystal structures of the CSD?

Name    Number
C       970,621
H       968,425
O       746,463
N       711,723
Cl      219,215
S       197,158
P       164,011
F       123,818
Cu      68,546

What is the CSD?

The CSD, or Cambridge Structural Database, is a collection of all the known crystal structures of organic and metal-organic compounds.  The database was started in 1965 as a collection of books. Today it has grown to nearly 1 million structures thanks to contributions from scientists around the world and is available online to everyone.

Who are the CCDC?

The Cambridge Crystallographic Data Centre is a non-profit organisation and independent charity who are responsible for maintaining the World's database for small molecule crystal structures. With over 70 staff in the UK and USA, they look after the database as well as creating state of the art software to help scientists understand the behaviour of atoms and molecules in crystals.

https://www.ccdc.cam.ac.uk/theccdcprofile/

Who are the BCA?

The British Crystallographic Association was formed in 1982 and is the UK’s national organisation for the science of crystallography. It represents over 700 scientists who are mainly based in the UK, who use crystallography as part of their career.

Do you want more information on crystallography?

https://m.youtube.com/watch?v=uqQlwYv8VQI

Do you want to try to grow your own crystals?

https://www.youtube.com/watch?v=HQNjGM2fTZs