Transition Elements (Chapter 24.1, 24.2 and 24.3) Flashcards
Where are the d-block elements located?
Between Group 2 and 13 of the periodic table
What are the d block elements in period 4?
Scandium to Zinc
What is true about the 3d sub-shell in d-block elements of period 4?
The 3d sub-shell has the highest energy and electrons are added to 3d orbitals (4s is already filled?
What are the characteristics of d-block elements?
The are metallic - ∴ they have metallic properties including a high melting and boiling point, shiny look and the ability to conduct electricity and heat
What is the electronic configuration of chromium?
1s2 2s2 2p6 3s2 3p6 4s1 3d5
What is the electronic configuration of copper?
1s2 2s2 2p6 3s2 3p6 4s1 3d10
Why do chromium and copper have unexpected electronic configurations?
Stability - a half filled 3d5 sub-shell and a fully filled 3d10 sub-shell gives additional stability to atoms of chromium and copper
What happens when the d block elements form positive ions from their atoms and what does this mean?
- They lose their 4s electrons before losing any of the 3d electrons
- ∴ when forming an atom, 4s orbitals fill before 3d orbitals
- ∴ when forming an ion, 4s orbitals empties before 3d orbitals
What are the transition elements?
D-block elements that form at least one ion with a partially filled orbital
Which two period 4 d-block elements are not transition elements and why?
Scandium and zinc bc:
1) scandium only forms Sc3+ ions by loss of two 4s and one 3d electrons, leaving empty d-orbitals (just 3p6)
2) zinc only forms Zn2+ by loss of its two 4s electrons, leaving a full d-orbtial (3d10)
What are the characteristic properties of transition metals that make then different from other metals?
1) they form compounds in which the transition element has different oxidation states
2) they form coloured compounds
3) the elements and their compounds can act as catalysts
Describe the characteristic of variable oxidation states of transition metals
1) the number of oxidation states increases across the transition elements to manganese and then decreases
2) all of the transition elements form compounds with an oxidation number of +2, resulting from the loss of two electrons
3) each oxidation state often has a characteristic colour
Describe the characteristic of the formation of coloured compounds by transition metals
1) the solid compounds can be dissolved in water to produce coloured solutions
2) the colour of a solution is linked to the energy levels of the partially filled d-orbitals of the transition metal ion which depend on the charge of the ion and the ligands involve - it can vary with different oxidation states
What colour is CoCl2?
Pink/purple
What colour is NiSO4?
Green
What colour is CuSO4?
Blue
What colours are Fe (II) and Fe (III)?
Fe (II) - pale green
Fe (III) - yellow
What colours are Cr (III) and Cr (VI)?
Cr (III) - green
Cr (VI) - yellow/orange
What are the common oxidation states that iron forms?
+2 and +3
What are the common oxidation states that chromium forms?
+3 and +6
Give 4 examples of how transition metals are used as heterogenous catalyst in industrial processes
1) Haber process is catalysed by an iron catalyst
2) Contact process is catalysed by vanadium oxide
3) Hydrogenation of vegetable fats to produce margarine is catalysed by nickel
4) Catalytic decomposition of hydrogen peroxide is catalyse by manganese dioxide
Describe two reactions catalysed by a transition metal as a homogenous catalyst
1) Reaction: S2O82- + 2I- => 2SO42- + I2 (ALL aqueous)
- Catalysed by aqueous Fe2+ ions:
S2O82- + Fe2+ => 2SO42- + Fe3+
Fe3+ + 2I- => I2 + Fe2+
2) Reaction: Zn + H2SO4 => ZnSO4 + H2
- Catalysed by aqueous Cu2+ ions
What is an important property of d-block elements?
The ability to form complex ions (other non d-block elements can also form them e.g. aluminium)
When is a complex ion formed?
When one or more molecules or negatively charged ions (ligands) bond to a central metal ion
What is a ligand?
- A molecule or ion that donates a pair of electrons to a central metal ion to form (via) a dative covalent bond/coordinate bond
- Some are neutral, some are negatively charged
What is a dative covalent bond/coordinate bond?
A covalent bond formed when one of the bonded atoms provides both of the electrons for the shared pair
What does the coordination number indicate?
The number of coordinate bonds attached to the central metal ion
How can water act as a ligand?
Each H2O molecule donates a lone pair of electrons from the oxygen atom to the central metal ion to form a coordinate bond
What is a monodentate ligand and what are the common examples?
- A ligand that is able to donate one pair of electrons to a central metal ion
- Neutral: H2O, NH3
- -1 charge: Cl-, CN-, OH-
What is a bidentate ligand?
A ligand that can donate two lone pairs of electrons to the central metal ion, forming two coordinate bonds
Describe the two common bidentate ligands
1) neutral: 1,2-diaminoethane (en) (NH2CH2CH2NH2) - each nitrogen atom donates a lone pair of electrons to the central metal ion forming a coordinate bond
2) 2- charge: ethandioate (oxalate) ion (COOCOO) - each negatively charged oxygen atom donates a lone pair of electrons to the central metal ion
What does the shape of a complex ion depend on?
Its coordination number (most common: 4 and 6)
Describe the shape of six-coordinate complexes
Octahedral shape with bond angles of 90 degrees
Describe the two possible shapes of four-coordinate complexes
1) tetrahedral (most common) - bond angles of 109.5 degrees around the central metal ion e.g. [Co/CuCl4]2-
2) square planar (least common) - bond angles of 90 degrees
- only occurs in complex ions of transition metals with 8 d-electrons in the highest energy d-sub-shell (platinum (II), palladium (II) and gold (III) e.g. [Pt(NH34]2+
What is stereoisomerism?
Molecules/compounds with the same structural formula but a different arrangement of atoms in space
What are the two types of stereoisomerism that complex ions can display and what does the type depend on?
1) cis-trans (geometric) isomerism
2) optical isomerism
- The type depends on the number and type of ligands attach to the central metal ion and the shape of the complex
What complex ions can show cis-trans isomerism?
- Some 4-coordiante and 6-coordinate complex ions containing different monodentate ligands
- Some square planar and octahedral complex ions
What complex ions can show both cis-trans and optical isomerism?
Some 6-coordinate complex ions containing monodentate and bidentate ligands
What is the difference between cis-trans isomerism in organic chemistry and in complex ions?
Unlike in organic chemistry, in complex ions no double bond is involved and the shape of the complex holds groups in different orientations about the central metal ion
Describe when cis-trans isomerism can occur in square planar complex ions
- The complex has no more than two identical ligands attached to the central metal ions
- The ligands are attained in the same plane at the corners of a square with 90 degree bond angles
- e.g. [Pd(NH3)2Cl2] formed from Pd2+, two NH3 and two Cl- ligands
Describe the cis-isomer of a square planar complex ion
Two identical groups are adjacent to each other and the coordinate bonds between the identical ligands are 90 degrees apart
Describe the trans-isomer of of a square planar complex ion
Two identical groups are opposite each other and the coordinate bonds between the identical ligands are 180 degrees apart
When can cis-trans isomerism occur in octahedral complex ions with at least two monodentate ligands?
When the complex contains four of one type of ligand and two of another type of ligand e.g. [Co(NH3)4Cl2]+ (monodentate) or [Co(NH2CH2CH2NH2)2Cl2]+
Describe the cis-isomer of an octahedral complex ion with at least monodentate ligands
The two identical ligands (e.g. Cl-) are adjacent with their coordinate bonds separated by 90 degrees
Describe the trans-isomer of an octahedral complex ion with at least monodentate ligands
The two identical ligands (e.g. Cl-) are opposite with their coordinate bonds 180 degrees apart
What is the colour of cis-[Co(NH3)4Cl2]+?
Violet
What is the colour of trans-[Co(NH3)4Cl2]+?
Green
What types of complex ions can form optical isomers?
Only the cis-isomers of octahedral complexes with 2 or 3 bidentate ligands
Why can only cis-isomers (not trans-isomers) form enantiomers?
Bc a mirror image of a trans-isomer is identical and can be super imposed
What is an important isomer and what is it used in?
Cis-platin used in the treatment of cancer
How is cis-platin used in cancer treatment?
1) cis platin attacks tumours and shrinks them
2) it does this by forming a platinum complex inside a cell which binds to DNA and prevents it from replicating
3) activation of the cell’s own repair mechanism eventually leads to apoptosis (systematic cell death)
Describe the structure of cis-platin
- cis-[Pt(NH3)2(Cl)2]
- Square planar
What is the problem with cis-platin?
- It has many unpleasant side-effects and can lead to kidney damage
- However, other clinical trials continue to find other platinum based drugs that may inhibit tumour growth without the side-effects
What makes transition elements good catalysts?
Their ability to change oxidation state
What is a complex ion?
A central metal ion surrounded by ligands
What is a simple ion spelt incorrectly?
A Leon: Someone who loves isabelle very very much because she is a pretty person with a gd bod.
