Chapter 24 - Transition elements Flashcards
What is the special case in writing the electron configurations for d-block elements?
a. The electron configurations of chromium and copper do not follow the expected principle for placing electrons singly in orbitals before pairing.
b. It is believed that a half-filled d5 sub-shell and a fully filled d10 sub-shell give additional stability to atoms of chromium and copper.
c. So, chromium has an electron configuration that ends in 3d54s1, whilst copper ends in 3d104s1.
How do we write the electron configurations of ions of d-block elements?
a. When forming an atom, the 4s orbital fills before the 3d orbitals.
b. When forming an ion, the 4s orbital empties before the 3d orbitals.
What is the definition of transition elements?
a. Transition elements are defined as d-block elements that form at least one ion with a partially filled d-orbital.
b. Although scandium and zinc are d-block elements, they do not match this definition and are not classified as transition elements.
c. Scandium only forms the ion Sc3+ by loss of two 4s electrons and one 3d electron and has an empty d orbital. d. Zinc only forms the Zn2+ ion by the loss of two 4s electrons and has a full d orbital.
What properties do transition metals have?
a. They form compounds in which the transition element has different oxidation states. i. For example, iron (II) chloride and iron (III) chloride.
b. They form coloured compounds. i. For example, Cr2O72- (Cr +6 oxidation state) is orange and Cr3+ is green (Cr +3 oxidation state).
c. The elements and their compounds can act as catalysts. i. For example, in the Haber process, the reaction between nitrogen and hydrogen is catalysed by a finely divided iron catalyst.
What is often the nature of a transition element in its highest oxidation state?
A species containing a transition element in its highest oxidation state is often a strong oxidising agent.
What is a catalyst?
a. A catalyst is a substance that increases the rate of a chemical reaction without itself changing. A catalyst works by providing an alternative reaction pathway with a lower activation energy.
b. A catalyst is left unchanged in the reaction.
What transition metal elements and compounds are used as catalysts?
a. Iron catalyst in the Haber process.
b. Vanadium (V) oxide in the contact process.
c. Nickel catalyst in the hydrogenation of vegetable fats in the manufacture of margarine.
d. Manganese (IV) oxide in the catalytic decomposition of hydrogen peroxide forming oxygen.
e. All of these are heterogeneous catalysts.
What is a heterogeneous catalyst?
It is a catalyst in a different physical state to the reactants.
What is a homogeneous catalyst?
It is where the catalyst is in the same physical state as the reactants.
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 a dative covalent bond.
What is a dative covalent bond or a coordinate bond?
A dative covalent or coordinate bond is where one of the bonded atoms provides both of the electrons for the shared pair.
What is the coordination number?
The coordination number is the number of coordinate bonds attached to the central metal ion.
What is a monodentate ligand and give some examples.
a. A monodentate ligand is a ligand that is able to donate one pair of electrons to a central metal ion.
b. Such examples include H20, NH3, Cl-, CN- and OH-.
What is a bidentate ligand and what are the most common examples?
a. A bidentate ligand is a ligand that can donate two lone pairs of electrons to the central metal ion, forming two coordinate bonds.
b. The most common bidentate ligands are 1,2-diaminoethane (frequently shortened to en) and the ethanedioate (oxalate) ion:
What is the colour of [CoCl4]2- and [CuCl4]2- complexes and what is the shape of these complexes?
The colour of [CoCl4]2- is a deep blue solution.
The colour of [CuCl4]2- is a yellow solution.
These complexes are a tetrahedral shape.
