Effective nuclear charge and radii Flashcards
What is the difference between Z and Zeff?
Zeff takes into account the screening effect of electrons that prevent an electron experiencing the full attraction of the nucleus (z).
How does Zeff vary as Z increases?
Zeff increases for a given PQN, as generally the increase in nuclear charge is not cancelled by the additional electron.
What is the definition of covalent radius of non-metallic elements?
1/2 the internuclear separation of neighbouring atoms of the same element in a molecule.
What is the definition of metallic radius?
1/2 the experimentally determined distance between nuclei of the nearest neighbouring atoms in the solid state.
What is ionic radius?
Measure of an ion size. It is related to the distance between neighbouring cations and anions, but is difficult to obtain and varies on the method used to establish the size of the ion.
Why do atomic radii increase down a group?
There is an increase in principal quantum number that means an increase in the number of radial nodes of R(r) which results in an increase of rdf max which moves further from the nucleus.
Why do atomic radii decrease as you go across a period?
As Zeff increases which pulls the electron cloud closer to the nucleus.
What is the Van Der Waals radius?
1/2 the internuclear distance of closest approach between two atoms of the same type in different molecules. This is the same as 1/2 the internuclear distance when the valence shells of non-bonded atoms of the same type are in contact.
What is ionisation energy?
The energy change on removing an electron from an atom to infinite distance in the gas phase (measured in eV).
What is electron affinity?
The reverse of ionisation potential and also quoted for the gas phase (measured in eV).
Why is there greater than expected decrease in radii from elements with atomic number 57 - 71?
F block contraction occurs, which is when f orbitals are poor screeners of electrons from the nuclear charge as they are large and diffuse.
Why do cations have a smaller radii than those for free atoms?
As they have closed outer shells with a smaller PQN than the element. This means there will be fewer radial notes and the rdf max will be closer to the nucleus than that of the atom.
Why are anions radii generally larger than those for free atoms?
As electrons are being added to a partially filled shell and more electron-electron repulsion occurs. There is no additional proton to offset this increase in electron.
