Transition Metals Flashcards
Is 3d or 4s subshell filled first and what are the exceptions?
- 4s before 3d because empty 3d subshell is at a higher energy than empty 4s
- Exceptions: Cr and Cu
- Repulsion between paired 4s electrons in higher energy and lower stability than half-filled or fully-filled d orbital
How do d-block elements form ions?
d-block elements form ions by losing 4s electrons first, followed by 3d electrons
Why do you fill 3d last but remove from 4s subshell for transition metals forming ions?
When the 3d orbitals are occupied by electrons, these electrons from inner shell repel the 4s electrons further away from the nucleus and to higher energy level
What is a transition element?
A transition element is a d-block element that forms at least one stable ion with a partially filled d subshell
What are elements are in d-block but are not transition elements?
-Sc³⁺: no electrons in 3d
-Zn²⁺: fully filled 3d
What elements do not show typical properties of transition elements in some oxidation states?
-Cu⁺ do not show typical properties of transition elements because it has a fully filled d subshell
What are the physical properties of transition elements?
-Hard
-high densities
-high melting and boiling points
Across the period, what is the trend of transition elements atomic radii?
-Across the period, electrons are being added to the inner 3d subshell
-these inner 3d electrons shield valence 4s electrons from the attraction of the nucleus
-thus the influence of each additional proton in the nucleus as the proton number increases across the group is reduced considerably
-as a result, increase in effective nuclear charge is negligible, atomic radii remain almost constant
What boiling points do transition elements have and why?
-very high melting and boiling points
-4s and 3d electrons are very close in energy, hence both can be contributed to form the sea of delocalised electrons, thus the metals form cations of higher charge
- ionic radii of transition elements cations are smaller than typical s-block elements
-more energy is required to overcome the stronger electrostatic forces of attraction between transition metal cations and sea of delocalised electrons, thus has high m.p. and b.p.
What are the densities of transition elements like and why?
d-block elements are generally denser than s-block elements because atoms are smaller and more tightly packed together
What is the trend of densities of transition elements across the period and why?
Gradual increase in density across the period as atomic radii generally decrease while relative atomic mass increase
What is the trend of ionisation energies like for transition elements across the period?
-small variation in first and second ionisation energies
- 1st and 2nd ionisation energies typically involve the removal of 4s electrons
- across the period, the additional 3d electrons which are inner shell electrons shield the 4s electrons from increasing nuclear charge
- thus the increase in effective nuclear charge is insignificant
What are the characteristic chemical properties of transition elements?
- variable oxidation states
- catalytic properties
- formation of complexes
- formation of coloured compounds and ions
Why do s-block element not have variable oxidation states?
s-block elements are limited to oxidation states of +1 and +2 because once the s electrons are removed, further removal of inner-shell p electrons requires too much energy
Why are transition elements able to exhibit variable oxidation states?
-the closeness in energy of 3d and 4s electrons meant that both 3d and 4s electrons are available for bond formation
What is formula for the maximum number of oxidation states for transition elements?
Max. no. of oxidation states = no. of 4s e⁻ + no. of unpaired 3d e⁻
What are lower oxidation states of transition elements usually found in?
ionic compounds
What are higher oxidation states of transition elements usually found in?
compounds or ions that contain covalent bonds
What is a catalyst?
A substance that increases the rate of a chemical reaction but remains chemically unchanged at the end of the reaction by providing an alternative pathway of lower activation energy
What are the two types of catalysts?
- homogenous catalyst
- heterogenous catalyst
What are homogenous catalyst?
Catalyst that operates in the same physical phase as the reactants
What are heterogeneous catalyst?
Catalyst that operates in different physical phase to the reactants
What are the characteristics of transition elements that allow them to function effectively as homogeneous catalysts?
- ability of transition element to exist in different oxidation states
- relative ease at which the oxidation state can be converted from one to another
What is usually the phase for catalyst and reactants for heterogeneous catalyst?
- catalyst is usually in solid phase and provides sites at which the reaction can occur
- reactants are usually liquids or gases
What are the characteristics of transition elements that enable them to function effectively as heterogeneous catalyst?
-availability of energetically accessible vacant 3d subshells which allow the ready exchange of electrons to and from reactant particles, thus facilitating the formation of weak bonds with reactant particles
- availability of 3d and 4s electrons for bond formation with reactant particles
What is a complex?
A complex contains a central metal atom or ion bonded to one or more surrounding ligands
What is a ligand?
A ligand is an ion or molecule which contains at least one atom bearing one lone pair of electrons which can be donated into the energetically accessible vacant orbital of the central metal or ion, forming a dative bond
What is complex ion?
If the complex carries an overall charge, it is a complex ion
What is coordination number of central metal atom or ion?
The number of co-ordinate bonds from the ligands to central atom or ion
Why is Fe²⁺ able to form dative bond with 4 or 6 ligands when its orbitals are all half-filled?
- For 4 ligands: 4s electron get move to 3d and get paired, resulting in 4 vacant orbitals (4s, 4p) to form 4 coordinate bonds
- For 6 ligands, 2 of the 3d e⁻ move and become paired, resulting in 6 empty orbitals to form 6 coordinate bonds (2 from 3d, 4s, 4p)
(just rmb it as electrons will basically squash itself and pair themselves to have vacant orbitals to form dative bonds)
How to name complex?
- Name cation then anion
- Name ligand before metal, if more than one ligand of the same kind present, indicate number of ligands by prefixes
- Name central atom and indicate oxidation state using roman numerals
What is the prefix name for H2O and what’s the co-ordinating atom?
aqua
H2O
What is the prefix name for NH3 and what’s the co-ordinating atom?
ammine
NH3
What is the prefix name for CO and what’s the co-ordinating atom?
carbonyl
CO
What is the prefix name for Cl⁻ and what’s the co-ordinating atom?
chloro
Cl⁻
What is the prefix name for CN⁻ and what’s the co-ordinating atom?
cyano
CN⁻
What is the prefix name for SCN⁻ and what’s the co-ordinating atom?
S-thiocyanato
SCN⁻
What is the prefix name for OH⁻ and what’s the co-ordinating atom?
hydroxo
OH-
What is the prefix name for H₂NCH₂CH₂NH₂ and what’s the co-ordinating atom?
ethane-1,2-diammine
H₂NCH₂CH₂NH₂
What prefix to use for the ligand?
di, tri, tetra, penta, hexa
or bis, tris, tetrakis
How to name the central atom in cationic and anionic complex?
Cationic complex: name of metal
Anionic complex: modify the name of the metal to end with “-ate”
What is the name of V in anionic complex?
vanadate
What is the name of Cr in anionic complex?
chromate
What is the name of Mn in anionic complex?
manganate
What is the name of Fe in anionic complex?
ferrate
What is the name of Cu in anionic complex?
cuprate
What is the name of Zn in anionic complex?
zincate
What is the name of Al in anionic complex?
aluminate
What is the name of Pb in anionic complex?
plumbate
What are ligands classified according to?
Number of co-ordinate bonds that the ligands form with central atom of ion