Module 5 (chapter 24) - transition elements Flashcards
background information about d-block elements
- are all metallic, displaying the typical physical properties of metals
- they have high melting and boiling points, shiny in appearance and conduct electricity and heat
uses of transition metals
- copper, silver, nickel and zinc have been used in coinage for many years
- iron is used in construction and the production of tools
- copper is used for electrical cables snd water pipes
- titanium is known for its great strength and use in aerospace and joint replacement
electron configuration of d-block elements
-the electron configuration of an atom or iron shows the arrangement of electrons in shells and sub shells
-electron occupy orbitals in order of increasing energy
-the electron configuration of chromium and copper don’t follow the expected principle for placing electron singly in orbitals before pairing
-this is due to stability
-a half filled d5 sub-shell and a fully filled d10 sub shell give additional stability to atoms
chromium (1s2,2s2,2p6,3s2,3p6,3d5,4s1)
copper (1s2,2s2,2p6,3s2,3p6,3d10,4s1)
rules when gaining and losing electrons
- when forming an atom, the 4s orbital fills before the 3d orbital
- when forming an ion, the 4s orbital empties before the 3d orbital
transition elements
they are d-block elements that form at least one ion with a partially filled d-orbital
-you can be a d-block element but not a transition element
why is scandium not a transition element?
scandium only forms Sc3+ ions by loss of two 4s electrons and one 3d electron
- it only has one electron in the 3d orbital and therefore its electron configuration becomes 1s2,2s2,2p6,3s2,3p6
- does not have a partially filled d orbital and so isn’t a transition element
why is zinc not a transition element?
- zinc only forms the Zn2+ ion by the loss of two 4s electrons
- the electron configuration of Zinc means that when these two electrons are lost it still has a full 3d shell snd so it is not half full.
properties of transition metals
- they form compounds in which the transition element has different oxidation states
- they form coloured compounds
- the elements and their compounds can act as catalysts
variable oxidation states
- transition elements form compounds with more than one oxidation state.
- iron forms two chlorides for example (iron(II) chloride and iron(III) chloride
- the number of oxidation states increases across the transition elements series to manganese, and then decreases.
- all of the transition elements form compounds with an oxidation number of +2, resulting from the loss of two electrons
formation of coloured compounds
- compound and ions of transition elements are frequently coloured
- potassium dichromate is bright orange
- cobalt (II)chloride is pink/purple
- nickel sulphate is green
- hydrated copper sulfate is blue
- the colour of a solution is linked the partially filled d-orbitals of the transition metal ion. the colour can vary with different oxidation states (e.g. iron)
catalysts
- iron is used to catalyse the hater process which manufactures ammonia
- vanadium oxide is used to catalyse the contact process and the production of surfer trioxide from surfer dioxide
- nickel is used yo catalyse the hydrogenation of vegetable fats when making margarine
- manganese oxide is used to catalyse the decomposition of hydrogen peroxide to form oxygen
what type of catalysts are the named transition metals
- heterogeneous catalysts
- some are homogeneous
- e.g. reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+ ions, with reactants and catalyst all in aqueous solution
- when the reaction is carried out with a trace of starch, a blue-black colour forms showing the formation of iodine. when catalyst added this precipitate forms much quicker
complex ions
d-block elements form complex ions
-other elements like aluminium can also form complex ions
how do complex ions form?
- when one of more molecules of negatively charged ions bond to a central metal ion. these molecules or ions are known as ligands
- the coordination number indicates the number of coordinate bonds attached to the central metal ion
ligand
a molecule of ion that donates a paid of electrons to a central metal ion to form a coordinate bond or date covalent bond
how are complex ions represented
- complex ion is enclosed inside square brackets with the overall change of the complex shown outside the square brackets
- the overall charge is the sum of the charges on the central metal ion and any ligand present.
monodentate ligands
-a ligand that is able to donate one pair of electrons to a central metal ion water (neutral) ammonia (neutral) chloride (-1) cyanide (-1) hydroxide (-1)
bidentate ligands
- ligands that can donate two lone pairs of electrons to the central metal ion, forming two coordinate bonds
- the most common are:
- 1,2 -diaminoethane (each nitrogen atom donates a paid of electrons to the central metal ion forming a coordinate bond)
- ethandioate (each negatively charged oxygen atom donates a lone pair of electrons to the central metal ion)
shapes of complex ions
- depends upon its coordination number. the commonest coordination numbers six and four
- many complex ions have a coordination number of six, given an octahedral shape (bond angles of 90 degrees)
four coordinate complexes
- tetrahedral complexes are the most common with bond angles of 109.5 degrees around the central metal ion (e.g. CoCl4 and CuCl4) both 2-
- square planar complexes occur in complex ions of transition metals with eight d electrons in the highest energy d sub shell (platinum, palladium and gold)
- Im this structure, ligands are arranged at the corners of a square
stereoisomers
complex ions can display two types of steriosiomerism
- cis/trans isomerism
- optical isomerism
- the type of stereoisomerism depends on the number and type of ligands that are attached to the central atom plus the shape of the complex
- some four coordinate and six coordinate complex ions containing two different types of monodentate ligands show cis-trans isomerism
- some six coordinate complex ions containing monodentate and bidentate ligands can show both cis/trans and optical isomerism
cis/trans isomerism in complex ions
- no C=C double bond is required and the shape of the complex holds groups in different orientations about the central metal ion
- occurs in square planar and octahedral complexes
cis-trans isomerism in quake planar complexes
- ligands are arranged in the same planes with 90 degree bond angles
- in the cis-isomer, the two identical groups are adjacent to each other, whereas in the trans isomer the two identical groups are opposite each other
- in the cis isomer the coordinate bonds between the identical ligands are 90 degrees apart vs 180 degrees in the trans-isomer
cis-trans isomerism in octahedral complexes
- complexes containing four of one type of ligand and two as another can show this. the cis isomer have identical glands adjacent to each other, the trans at 180 degrees
- octahedral complexes containing bidentate ligands can also shoe cis-trans isomerism
- if the other two atoms (not bidentate) are nest to each other is it cis, if they are opposite it is trans