You can edit the radius of atoms of that element type using the radius field ' r '.Д®diting the radii for all oxygen atoms in a structure, using CrystalMaker's Atoms Inspector. Each element row has a colour button, which you can use to change the colours for all atoms with that element type. The pane shows an hierarchical listing of element types and sites. You can easily change the colour and/or radius of a crystal site, or group of sites, using CrystalMaker's Atoms Inspector (to make this visible, choose: View > Inspector > Atoms). Whilst the standard CPK colours are limited to the elements found in organic compounds, CrystalMaker's VFI Atomic Radii, CSD Default Radii and Shannon & Prewitt Crystal Radii Element Tables provide a more diverse range of contrasting colours. Many organic chemists use the so-called CPK colour scheme These colours are derived from those of plastic spacefilling models developed by Corey, Pauling and (later improved on by) Kultun ('CPK'). Of course, atoms don't have 'colour' in the conventional sense, but various conventions have been established in different disciplines. Shannon RD (1976) Acta Crystallographica A23:751-761 The Colours of AtomsД¬olour-coding atoms by element type is an important way of representing structural information. Shannon RD Prewitt CT (1969) Acta Crystallographica B25:925-946 These data, originally derived from studies of alkali halides, are appropriate for most inorganic structures, and provide the basis for CrystalMaker's default Element Table. Perhaps the most authoritative and highly-respected set of atomic radii are the 'Crystal' Radii published by Shannon and Prewitt (1969) - one of the most cited papers in all crystallography - with values later revised by Shannon (1976).

Slater JC (1964) Journal of Chemical Physics 39:3199- Crystal Radii The bond length between atoms A and B is the sum of the atomic radii,Д¬rystalMaker uses Atomic-Ionic radii data from: For example, the atomic-ionic radius of chlorine (Cl -) is larger than its atomic radius. These are the 'realistic' radii of atoms, measured from bond lengths in real crystals and molecules, and taking into account the fact that some atoms will be electrically charged. CrystalMaker uses Van-der-Waals Radii data from:Д«ondi A (1964) Journal of Physical Chemistry 68:441- Atomic-Ionic Radii

Van-der-Waals radii are determined from the contact distances between unbonded atoms in touching molecules or atoms. Whilst this is straightforward for some molecules such as Cl 2 and O 2, in other cases one has to infer the covalent radius by measuring bond distances to atoms whose radii are already known (e.g., a C-X bond, in which the radius of C is known).Д¬rystalMaker uses covalent radii listed on CrystalMaker-user Mark Winter's excellent Web Elements website. The covalent radius of an atom can be determined by measuring bond lengths between pairs of covalently-bonded atoms: if the two atoms are of the same kind, then the covalent radius is simply one half of the bond length. Springer Verlag, Berlin.Д¬lementi E, Raimondi DL, Reinhardt WP (1963). Vainshtein BK, Fridkin VM, Indenbom VL (1995) Structure of Crystals (3rd Edition). CrystalMaker uses Atomic radii data from two sources: Although more electrons are being added to atoms, they are at similar distances to the nucleus and the increasing nuclear charge 'pulls' the electron clouds inwards, making the atomic radii smaller.ДЄtomic radii are generally calculated, using self-consistent field functions. Atomic radii decrease, however, as one moves from left to right, across the Periodic Table.

The general trend is that atomic sizes increase as one moves downwards in the Periodic Table of the Elements, as electrons fill outer electron shells. Atomic RadiiДЄtomic radii represent the sizes of isolated, electrically-neutral atoms, unaffected by bonding topologies. In the following article we'll explore a number of different sets of distinct atomic radius sizes, and later we'll see how you can make use of these 'preset' values with CrystalMaker. Take the humble carbon atom as an example: in most organic molecules a covalently-bonded carbon atom is around 1.5 Г…ngstroms in diameter (1 Г…ngstrom unit = 0.1 nanometres = 10 -10 metres) but the same atom in an ionic crystal appears much smaller: around 0.6 Г…ngstroms. However, even for atoms of the same type, atomic radii can differ, depending on the oxidation state, the type of bonding and - especially important in crystals - the local coordination environment. To a first approximation we can regard atoms as 'hard spheres', with an outer radius defined by the outer electron orbitals. How big is an atom? A simple question maybe, but the answer is not at all straighforward.

Largest to smallest atomic radius