MARY - Topic 8 Flashcards
What is the covalent radius of a non-metallic element?
1/2 the internuclear separation of neighbouring atoms of the same element in a molecule
What is the metallic radius?
1/2 the experimentally determined distance between nuclei, of nearest neighbour atoms in the solid state.
What is ionic radius?
A measure of an ion size, and is related to the distance between neighbouring cations and anions.
Why does atomic radii generally get larger as you go down a group?
1 = increase in PQN means an increase in radial nodes resulting in an increase in the rdf max, so moves further from the nucleus.
Why does atomic radii generally get smaller as you go across a period?
1 = Zeff increases, pulling the e- cloud closer to the nucleus, so rdf max is closer to nucleus.
2 = This causes f-block contraction and d-block contraction.
3 = F-orbitals are poor screeners of electrons from nuclear charge because f-orbitals are diffuse.
What happens in the d-block?
The net effect is that while 4d elements have larger atomic radii than 3d elements, the poor screening effect of the f-orbitals mean that 4d + 5d elements in the same group have similar radii.
What is a van der waals radius?
1/2 internuclear distance of closest approach between two atoms of the same type in different molecules.
This is the same as the 1/2 internuclear distance when the valence shells of non-bonded atoms of the same type are in contact.
What is the ionisation energy?
Energy change on removing an electron from an atom to infinite distance in the gas phase. (eV)
What is the ionisation enthalpy?
The standard enthalpy change per mole for this process.
What is electron affinity (Ae)?
Reverse of ionisation potential in the gas phase. (eV)
Why do cations generally have smaller radii than free atoms?
They have closed outer shells with a smaller PQN than the element, so for an element with a PQN = n, the ion will have electrons in shells up to PQN = n-1. This means orbitals have fewer radial nodes, so rdf max for cation is closer to the nucleus.
Why do anions generally have larger radii than free atoms?
E-‘s are being added to an already partially filled shell, causing e-e repulsion which isn’t offset by the addition of a H+ to the nucleus. So Zeff is smaller, so has a larger ionic radius.
What is electronegativity?
the power of an atom to attract electrons to itself when it’s part of a compound
What happens to electronegativity?
Increases across the period as Zeff is increasing, and decreases down groups as increase in PQN causes outer e-‘s to be screened from the nuclear charge.
What is ionic bonding?
Material is made of cations and anions, where an electron is transferred from one atom which then becomes a cation, to another to make this an anion.
