Transition Elements

Question 1

Compare the melting point/boiling point of transition elements and s-block elements. Explain.

Answer 1

Transition elements have higher melting points/boiling points than s-block elements.

For TM, both 4s and 3d valence electrons are available for delocalisation due to their similar energy levels, while for s-block elements, only 1 or 2 valence electrons from 4s orbitals are available for delocalisation. [number of electrons available]

Thus, more energy is required to overcome stronger metallic bonding, i.e. efoa between metal cations and sea of delocalised 3d and 4s electrons in TM, compared to the weaker metallic bonding, i.e. efoa between metal cations and sea of delocalised 4s electrons in s-block elements. [strength of metallic bond, amount of energy to overcome]

Question 2

Describe and account for the trend in atomic radius for first row transition elements.

Answer 2

Atomic radius is relatively INVARIANT across first row TM.
Why?
- electrons are added to the penultimate 3d orbitals
- the increase in shielding effect from 3d electrons almost cancels out the increase in nuclear charge (due to increasing no. of protons)
- effective nuclear charge remains relatively invariant
- thus atomic radius is relatively invariant.

Question 3

What is a transition element?

Answer 3

A transition element is a d-block element that is able to form one or more stable ions with partially filled d subshells.

Question 4

How do homogeneous catalysts usually act in a reaction??

Answer 4

A homogeneous catalyst is in the same phase as reactants.
It (the element) is able to exist in various oxidation states.
It usually lowers the activation energy by forming intermediates that involve collisions between two oppositely-charged ions, instead of two negatively charged / two positively charged ions.

Question 5

State the electronic configuration of Cu (29 electrons). (hint: in the ground state)

Answer 5

[Ar]3d10.4s1

Question 6

Why does Cr6+ (aq) ion not exist but CrO4 2-(aq) ions are formed instead?

Answer 6

Cr6+ has very high charge density, so it polarises the electron cloud of water ligands, undergoing hydrolysis extensively to form CrO4 2-(aq) ions.