Flashcards in Module 5: Chapter 24 (Transition Elements) Deck (55)
Where are d-block elements found on the periodic table?
between Group 2 and Group 13
What is the highest energy level for period 4?
from Sc to Zn 3d sub-shell has the highest energy level
What are d-block elements?
- all metals, form metallic bonds
- good conductors of heat and electricity
- high melting and boiling points
What are some uses of d-block elements?
Cu, Ni, Zn and Ag are used in coins
Fe is used to make steel used in construction and tool making
Cu is used in water pipes and electrical wiring
What is the electron configuration of chromium?
- half filled d-subshell
What is the electron configuration of copper?
[Ar] 3d10 4s1
- fully filled d sub-shell
Why do chromium and copper have half and fully filled sub-shells?
It is believed that the half-filled or fully filled d sub-shell gives additional stability to atoms of chromium and copper
When elements between Sc and Zn form ions, are electrons lost from 3d sub-shell first?
4s empties before 3d orbitals when forming an ion (4s fills before 3d when forming an atom, first in first out)
What are transition elements?
d-block elements that form at least one ion with a partially filled d-orbital
Why are Zn and Sc not transition elements?
both only form one ion without a partially filled d-orbital
Sc3+ = 1s2 2s2 2p6 3s2 3p6 (empty d-orbitals)
Zn2+ = 1s2 2s2 2p6 3s2 3p6 3d10 (full d-orbitals)
What are the properties of transition elements and their compounds?
1. they can form compounds in which the transition element has different oxidation states
2. they form coloured compounds
3. many transition elements and their compounds can act as catalysts
Transition element property: variable oxidation states
- each oxidation state has a characteristic colour
- the number of oxidation states increases across the series to manganese and then decreases
- a species containing a transition element in its highest oxidation state is often a strong oxidising agent (e.g. manganate (VII) ion MnO4^-)
Transition element property: formation of coloured compounds
- compounds and ions of transition metals are frequently coloured
- e.g. potassium dichromate (VI) is orange and hydrated copper (II) sulfate is blue
- solid compounds can be dissolved in water to produce coloured solutions
- colour of a solution is linked to the partially filled d-orbitals of the transition metal ion
Define what a catalyst does?
A catalyst is a substance that increases the rate of a chemical reaction without itself changing. It works by providing an alternative reaction pathway of lower activation energy.
Give an example of where a heterogeneous catalyst is used in industry?
- an iron catalyst used in the Haber Process to make ammonia
- Vanadium (V) Oxide (V2O5) is used in the Contact Process (manufacture of sulfuric acid), catalyses the reaction of 2SO2 + O2 <=> 2SO3
- Nickel used in the hydrogenation of vegetable oils to make margarine
What is meant by a heterogeneous catalyst?
The catalyst is in a different state to the reactants
Transition elements property: catalysts
- Reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+(aq) ions
S2O8^2-(aq) + 2I-(aq) -> 2SO4^2-(aq) + I2(aq)
- How Fe2+ catalyses reaction...
Fe2+ reacts: S2O8^2- + Fe2+ -> 2SO4^2- + Fe3+
Fe2+ regenerated: Fe3+ + 2I- -> I2 + Fe2+
- Reaction of zinc metal with acids is catalysed by the presence of Cu2+(aq) ions
What is an orbital?
A region around a nucleus where there is a high probability of finding an electron
- an orbital can hold up to 2 electrons with opposite spin
Describe an s-orbital?
- sphere shape
- one occurs in every principal energy level
Describe a p-orbital?
- dumb-bell shaped
- 3 orbitals in the z, y and x axis
- 3 orbitals occur in energy levels except the first
What is a complex ion
A complex ion is formed when one or more molecules or negatively charged ions (ligands) bond to a central metal ion
What is a ligand?
A ligand is a molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or dative covalent bond
What is a coordinate/dative covalent bond?
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
What is the coordination number?
The coordination number indicates the number of coordinate bonds attached to the central metal ion
What is a monodentate ligand?
Able to donate one pair of electrons to a central metal ion
What are the 5 common monodentate ligands?
Water (H2O:) neutral charge
ammonia (:NH3) neutral charge
chloride (:Cl-) 1- charge
cyanide (:CH-) 1- charge
hydroxide (:OH-) 1- charge
: = which atom the lone pair is found on
What is a bidentate ligand?
able to donate 2 pairs of electrons to a central metal ion
What are the 2 common bidentate ligands?
1. Ethanedioate (oxalate), (C2O4)2-
- usually forms coordination number of 6
- the negatively charged oxygens donate lone pairs to metal ion (other two oxygens have a double bond each with a carbon)
2. 1,2-diaminoethane (shortened to en), H2NCH2CH2NH2
- lone pairs found on both nitrogen atoms
- coordination number is normally 6
What to remember when drawing complex ions?
- central metal ion (no charge)
- ligans (bonded to correct atom)
- 3D shape always
- lone pairs and dative bonds
- brackets with an overall charge of ion