Chemistry of the elements Flashcards
At La in the periodic table what happens? (what is La electron configuration?)
La 6s2 5d1
Instead of filling remainder of 5d orbital next electron goes into 4f at Ce
Then fill 4f1-14, then complete 5d filling
At Ac what happens?
Ac 7s2 6d1, next orbital to be filled is 5f
If an electron is in the same principal quantum shell…
Shielding is small ie. 2s don’t shield 2p well
What is d block contraction?
d electrons don’t shield each other very well so filling d1-d10 results in significant increase in zeff across period
Has fundamental effect on p-block elements
Why is the 4s orbital filled before the 3d?
Effective nuclear charge is greater due to regions of probable electron density near the nucleus (4s e- density penetrates e- cloud)
Why are electrons removed first from d orbitals in transition metals?
After 4s, 3d fills but falls sharply in energy as 4s doesn’t shield 3d effectively
The 3d shields the 4s so 4s are high in energy
3d electrons become core-like and don’t play a role in chemistry of following 4p electrons
What are relativistic effects?
The mass of an electron increases as atomic number increases
Thus (due to equations we don’t have to know) size and energy of orbital drops at Pt, Au elements
NB in s orbitals relativistic orbital contractions are most pronounced as wavefunctions non-zero at nucleus so nuclear charge experienced more
In Au high relativistic shielding of 6s orbital results in higher energy of d and f orbital
What is a covalent radius?
Radius of atom within homoatomic bond
NB for some elements these don’t exist so have to approximate with bond to similar element
What is a metallic radius?
Half the internuclear distance within a metallic lattice, depends on type of packing occurring, usually 12-coordinate bond listed in tables
What is an ionic radius?
Size of atom in crystal lattice, determined via looking at minima in xray structure
What is drawback of looking at x-ray structure for ionic rad?
Assumes ‘hard-sphere’ model but there is always some covalent character of an ionic lattice where cation and anion clouds interpenetrate
What 3 factors does ionic size depend on?
Charge, oxidation state, coordination number
What is a vdw radius?
Half the nearest contact difference between atoms in which dispersion forces only are at work
(see notes for diagram)
Inherently loosely defines as vdw forces are weak and non-directional hence wide range of values
Describe covalent radii trends across period
For n=1,2,3 there is a drop in size and total size drop= 0.6 A
n=4 and n=5 d-block contraction means higher Zeff and bigger drop in size, 0.9 A (0.3 A due to d-block contraction)
